Topic 10 · Chemical formulas — the scripts

What you are deciding: go-ahead for video generation on this topic, card by card.

Out of scope: articles and PP100 items (not on this page).

Here: the intro video, 5 lesson videos (3 marked by the author as “could do without a video”) and the summary video, in teaching order. Each card: the script, the attached question, then the quiz the student meets after the video.

How: tap one button per card. Taps and notes save as you go and are sent; the Notes tab shows what has gone and re-sends.

Intro video · teaches nothing, opens the question93 words · about 0:46

Introduction: Chemical formulas

Script

Say	Screen
A water bottle is labeled H₂O.	[the water bottle; its label]
A brown bottle in the bathroom is labeled H₂O₂.	[the brown bottle beside it; its label]
The two labels are one small 2 apart.	[the two labels side by side; the extra 2 glows]
But you drink the first, and the second bleaches hair.	[a glass of water; a bleached streak of hair]
Chemists write every substance with letters and small numbers like these.	[a row of labels: H₂O, CO₂, NaCl]
So how does one small number turn a drink into a bleach?	[question mark over the two labels]
To find out, we will look at what the letters and the numbers on a label say, and how to count with them.	[the two labels stay]
Okay, so are you ready to crack the code on the bottles?	[the three replies appear]

The ready line's poll — the attached item (no key; the intro teaches nothing)

video

Okay, so are you ready to crack the code on the bottles?

A Yes, let's go! — Great. Here we go.
B Not sure yet — That's fine. We take it one letter and one number at a time.
C Let me watch that again — Good idea. Watch it again, then come back.

Answer

No key. A poll: every reply is accepted with its friendly line.

Your note · the intro video

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 1 of 5Author: definitely a video197 words · about 1:38

What a formula says

MAT-059 · What a chemical formula tells you — Explain what the symbols and subscripts in a chemical formula represent.

Script

Say	Screen
A water bottle is labeled H₂O, and a fire extinguisher is labeled CO₂.	[the bottle and the extinguisher; the two labels]
Here is one water particle drawn as circles: one large open circle joined to two small dark ones.	[the water particle; key: large open = oxygen, small dark = hydrogen]
The label writes the same particle as a letter, a small 2 and another letter.	[H₂O beside the particle]
What does each letter say?	[the H and the O glow; question mark]
Every element has a chemical symbol, so H is hydrogen and O is oxygen.	[H — hydrogen; O — oxygen]
Each atom lines up under its own letter.	[the two hydrogen atoms slide under the H; the oxygen atom slides under the O]
And what does the small 2 count?	[the 2 glows; question mark]
It sits low after the H and counts the atoms of the element just before it: 2 hydrogen atoms.	[the 2 boxed; the two small dark circles ringed]
A small number written low after a symbol is called a subscript.	[chip: SUBSCRIPT]
The O has no subscript, so the O counts one oxygen atom.	[the O; label: 1 oxygen atom]
This way of writing a substance is called its chemical formula.	[chip: CHEMICAL FORMULA; H₂O = 2 hydrogen atoms + 1 oxygen atom]
Now consider CO₂: C is carbon and O is oxygen.	[CO₂ beside its particle: the gray circle onto the C, the two large open circles onto the O]
The 2 after the O counts 2 oxygen atoms.	[the 2 boxed; the two large open circles ringed]
So, a chemical formula writes one particle of a substance.	[the rule slide: H₂O and CO₂ with their particles; chips CHEMICAL FORMULA, SUBSCRIPT, O = 1 oxygen atom; nothing else printed]
Each symbol names one element in the particle, and a subscript counts the atoms of the element just before it.	[the symbols and the subscripts glow in turn]
So each of the two labels writes one particle.	[the bottle and the extinguisher; the particles beside the labels]
Okay, now your turn.	[closing screen: bullets — • A chemical formula writes one particle of a substance • Each symbol names one element in the particle • A subscript counts the atoms of the element just before it]

“Okay, now your turn.” — the attached question

video

A water bottle is labeled H₂O. What does the small 2 count?

A hydrogen atoms
B oxygen atoms
C water particles

Answer

Key: A — hydrogen atoms

A subscript counts the atoms of the element just before it.
The 2 comes just after the H.
So the 2 counts 2 hydrogen atoms.

Feedback per option

A The 2 sits just after the H, so it counts hydrogen atoms: 2 hydrogen atoms.
B The 2 comes after the H, not the O; the O with no subscript is 1 oxygen atom.
C A subscript counts atoms in one particle, not particles.

Quiz after the video — the mastery check, 13 items

Q1recall

A label reads KBr. How many elements does KBr name?

A one element
B two elements

Answer

Key: B — two elements

Every capital letter starts a new chemical symbol.
KBr has two capital letters: the K and the B.
So KBr is two symbols, potassium and bromine: two elements.

Feedback per option

A KBr has two capital letters, K and B, so it names two elements: potassium and bromine.
B Every capital letter starts a new symbol. KBr has two capitals, K and B: two elements, potassium and bromine.

Q2recall

Every particle of a substance holds two kinds of atom joined together in a fixed pattern. What kind of substance is it?

A a compound
B an element
C a mixture

Answer

Key: A — a compound

The particles hold two kinds of atom.
The two kinds are joined together in a fixed pattern.
A substance made of two or more kinds of atom joined together in a fixed pattern is called a compound.

Feedback per option

A Two or more kinds of atom joined together in a fixed pattern make a compound.
B An element has only one kind of atom; this substance has two kinds joined.
C In a mixture the substances are mingled, not joined; here the two kinds of atom are joined.

Q3term

Chemists write one particle of a substance as symbols and small low numbers, for example CO₂. This way of writing a substance is called its…

Typed answer

Answer

Accepted: chemical formula · formula · a chemical formula · the chemical formula · its chemical formula · a formula · the formula

The symbols name the elements, and the small numbers count the atoms.
This way of writing one particle of a substance is called its chemical formula.

Q4term

In CO₂, the small 2 is written low, just after the O. What is a small number written like this called?

Typed answer

Answer

Accepted: subscript · a subscript · the subscript

The 2 is written small and low, after a symbol.
A small number written low after a symbol is called a subscript.

Q5what

H₂S is the gas that smells of rotten eggs. In H₂S, what does the H tell you?

A the element hydrogen is in the particle
B the number of atoms in the particle

Answer

Key: A — the element hydrogen is in the particle

Each symbol in a formula names one element.
H is the chemical symbol for hydrogen.
So the H tells you the particle holds hydrogen.

Feedback per option

A H is hydrogen's chemical symbol, so the H names the element hydrogen.
B A symbol names an element, not a number; the count is in the subscript after it.

Q6what

In H₂S, which atoms does the small 2 count?

A hydrogen atoms
B sulfur atoms

Answer

Key: A — hydrogen atoms

A subscript counts the atoms of the element just before it.
The 2 comes just after the H.
So the 2 counts hydrogen atoms: 2 hydrogen atoms.

Feedback per option

A The 2 comes just after the H, so it counts hydrogen atoms: 2 hydrogen atoms.
B A subscript counts the element just before it. The 2 comes after the H, not the S, so it counts hydrogen atoms.

Q7what

In H₂S, the S has no subscript after it. How many sulfur atoms does one particle hold?

A no sulfur atoms
B 1 sulfur atom
C 2 sulfur atoms

Answer

Key: B — 1 sulfur atom

The S has no subscript after it.
A symbol with no subscript counts one atom.
So one particle holds 1 sulfur atom.

Feedback per option

A The S is in the formula, so sulfur is in the particle; no subscript means one atom, not none.
B A symbol with no subscript counts one atom: 1 sulfur atom.
C The 2 comes after the H and counts hydrogen atoms; the S has no subscript, so 1 sulfur atom.

Q8what

N₂O is the laughing gas a dentist may use. How many nitrogen atoms does one N₂O particle hold?

Typed answer

Answer

Accepted: 2 · 2 nitrogen atoms · two · 2 atoms

The 2 comes just after the N.
A subscript counts the atoms of the element just before it.
So one N₂O particle holds 2 nitrogen atoms.

Q9what

Touching circles are joined. In this drawing, gray circles are carbon atoms, small dark circles are hydrogen atoms and large open circles are oxygen atoms. Which formula writes this particle?

A CHO
B CHO₂
C CH₂O

Answer

Key: C — CH₂O

Count the circles of each kind: 1 gray circle, 2 small dark circles and 1 large open circle.
So the particle holds 1 carbon atom, 2 hydrogen atoms and 1 oxygen atom.
The subscript after the H counts the hydrogen atoms: CH₂O.

Feedback per option

A CHO would be 1 atom of each kind; the drawing has two small dark circles, so 2 hydrogen atoms.
B CHO₂ would need 2 oxygen atoms; the drawing has one large open circle and two small dark circles, so the 2 belongs after the H.
C One gray circle, two small dark circles and one large open circle: 1 carbon atom, 2 hydrogen atoms and 1 oxygen atom, CH₂O.

Q10what

Touching circles are joined. In this drawing, gray circles are carbon atoms and large open circles are oxygen atoms. Which formula writes this particle?

A CO₂
B CO
C C₂O

Answer

Key: B — CO

Count the circles of each kind: 1 gray circle and 1 large open circle.
So the particle holds 1 carbon atom and 1 oxygen atom.
A symbol with no subscript counts one atom, so the formula is CO.

Feedback per option

A CO₂ would need 2 oxygen atoms; the drawing has one large open circle, 1 oxygen atom.
B One gray circle and one large open circle: 1 carbon atom and 1 oxygen atom, no subscripts, CO.
C C₂O would need 2 carbon atoms; the drawing has one gray circle, 1 carbon atom.

Q11misconception

Idris says: "In H₂O, the small 2 counts the oxygen atoms." Is Idris correct?

A yes
B no

Answer

Key: B — no

A subscript counts the atoms of the element just before it.
The 2 comes just after the H, so the 2 counts 2 hydrogen atoms.
The O has no subscript, so there is 1 oxygen atom, and Idris is not correct.

Feedback per option

A A subscript counts the element just before it. The 2 comes after the H, so it counts hydrogen atoms, not oxygen atoms.
B The 2 comes just after the H, so it counts 2 hydrogen atoms; the O, with no subscript, is 1 oxygen atom.

Q12misconception

Yuki says: "In CO₂, the C has no subscript, so one particle holds 1 carbon atom." Is Yuki correct?

A yes
B no

Answer

Key: A — yes

The C has no subscript after it.
A symbol with no subscript counts one atom.
So one CO₂ particle holds 1 carbon atom, and Yuki is correct.

Feedback per option

A The C has no subscript, and a symbol with no subscript counts one atom: 1 carbon atom.
B A symbol with no subscript still counts one atom, so the C counts 1 carbon atom.

Q13transfer

NO₂ is a brown gas in car exhaust. Read NO₂ as counts of atoms in one particle. Which reading is correct?

A 2 nitrogen atoms and 1 oxygen atom
B 2 nitrogen atoms and 2 oxygen atoms
C 1 nitrogen atom and 2 oxygen atoms

Answer

Key: C — 1 nitrogen atom and 2 oxygen atoms

The N has no subscript, so it counts 1 nitrogen atom.
The 2 comes just after the O, so it counts 2 oxygen atoms.
So one NO₂ particle holds 1 nitrogen atom and 2 oxygen atoms.

Feedback per option

A The 2 comes after the O, not the N, so it counts oxygen atoms; the N has no subscript: 1 nitrogen atom.
B The N has no subscript, so 1 nitrogen atom; only the O carries the 2.
C The N has no subscript: 1 nitrogen atom. The 2 after the O counts 2 oxygen atoms.

Your note · lesson 1: What a formula says

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 2 of 5Author: could do without a video188 words · about 1:34

Count the atoms in a formula

MAT-060 · Count atoms in a simple formula — Count the number of atoms of each element in a formula that contains only subscripts.

Script

Say	Screen
A food-science book lists glucose, the sugar in grapes, as C₆H₁₂O₆.	[the book page; C₆H₁₂O₆ large]
One glucose particle is built from many atoms: how many of each element, and how many in all?	[four blanks: C ?, H ?, O ?, all ?]
The formula tells you, in three steps.	[1, 2, 3 as bold numbers]
A formula writes one particle, and each subscript counts that element's atoms.	[H₂O with its particle; the 2 boxed]
One: take the symbols one at a time: C, then H, then O.	[C, H, O light up in turn]
Two: read the subscript after each symbol: that subscript is that element's count.	[6, 12, 6 boxed in turn]
C₆ is 6 carbon atoms, H₁₂ is 12 hydrogen atoms, and O₆ is 6 oxygen atoms.	[table rows fill: carbon 6, hydrogen 12, oxygen 6]
Three: add the counts for the total: 6 plus 12 plus 6 is 24 atoms in one glucose particle.	[total row: 24]
Now consider methane, CH₄: the C with no subscript is 1 carbon atom.	[CH₄ beside its particle; table row: carbon 1]
The 4 after the H is 4 hydrogen atoms: 5 atoms in all.	[the 4 boxed; table row: hydrogen 4; total 5]
So, to count the atoms in a formula, take the symbols one at a time, read each subscript as that element's count, and add the counts for the total.	[the rule slide: the glucose counting table; nothing else printed]
So glucose is 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms: 24 atoms in one particle.	[the four blanks filled]
Okay, now your turn.	[closing screen: bullets — • Take the symbols one at a time • Read each subscript as that element's count • Add the counts for the total]

“Okay, now your turn.” — the attached question

video

Glucose is C₆H₁₂O₆. How many atoms are in one glucose particle in all?

A 6
B 12
C 24

Answer

Key: C — 24

Read the three subscripts: 6, 12 and 6.
Add the counts: 6 + 12 + 6 = 24.
So one glucose particle holds 24 atoms.

Feedback per option

A 6 is the carbon count, or the oxygen count; the total adds all three.
B 12 is the hydrogen count alone; the total adds all three.
C 6 carbon atoms + 12 hydrogen atoms + 6 oxygen atoms = 24 atoms.

Quiz after the video — the mastery check, 13 items

Q1recall

In a chemical formula, what does a subscript count?

A the atoms of the element just before it
B the atoms of the element just after it
C the particles of the substance

Answer

Key: A — the atoms of the element just before it

A subscript is written just after a symbol.
It counts the atoms of that element in one particle.
So a subscript counts the atoms of the element just before it.

Feedback per option

A A subscript counts the atoms of the element whose symbol comes just before it.
B A subscript belongs to the symbol before it, not after it.
C A subscript counts atoms in one particle, not particles.

Q2scaffold

Propane, the gas in a camping stove, is C₃H₈. Which elements does C₃H₈ name?

A carbon and hydrogen
B carbon only

Answer

Key: A — carbon and hydrogen

Take the symbols one at a time: C, then H.
C is carbon and H is hydrogen.
So C₃H₈ names carbon and hydrogen.

Feedback per option

A Two capital letters, C and H: two elements, carbon and hydrogen.
B The H is a second symbol, so a second element, hydrogen, is in the particle.

Q3scaffold

In C₃H₈, read the subscript after the C. How many carbon atoms does one propane particle hold?

Typed answer

Answer

Accepted: 3 · 3 carbon atoms · three · 3 atoms

The subscript after the C is 3.
A subscript counts the atoms of the element just before it.
So one propane particle holds 3 carbon atoms.

Q4scaffold

In C₃H₈, read the subscript after the H. How many hydrogen atoms does one propane particle hold?

Typed answer

Answer

Accepted: 8 · 8 hydrogen atoms · eight · 8 atoms

The subscript after the H is 8.
A subscript counts the atoms of the element just before it.
So one propane particle holds 8 hydrogen atoms.

Q5scaffold

Add your two counts for C₃H₈ together. How many atoms in all does one propane particle hold?

Typed answer

Answer

Accepted: 11 · 11 atoms · eleven · 11 atoms in all

One propane particle holds 3 carbon atoms and 8 hydrogen atoms.
Add the counts: 3 + 8 = 11.
So one propane particle holds 11 atoms.

Q6bare

Ammonia, a sharp-smelling gas in some cleaners, is NH₃. How many hydrogen atoms does one ammonia particle hold?

Typed answer

Answer

Accepted: 3 · 3 hydrogen atoms · three · 3 atoms

The subscript after the H is 3.
So one ammonia particle holds 3 hydrogen atoms.

Q7bare

Hydrogen peroxide, the liquid that bleaches hair, is H₂O₂. How many oxygen atoms does one hydrogen peroxide particle hold?

Typed answer

Answer

Accepted: 2 · 2 oxygen atoms · two · 2 atoms

The subscript after the O is 2.
So one hydrogen peroxide particle holds 2 oxygen atoms.

Q8bare

Seashells and eggshell are calcium carbonate, CaCO₃. How many oxygen atoms does one CaCO₃ particle hold?

Typed answer

Answer

Accepted: 3 · 3 oxygen atoms · three · 3 atoms

The subscript after the O is 3.
So one CaCO₃ particle holds 3 oxygen atoms.

Q9bare

Table salt is NaCl. How many atoms in all does one NaCl particle hold?

Typed answer

Answer

Accepted: 2 · 2 atoms · two

Na has no subscript: 1 sodium atom. Cl has no subscript: 1 chlorine atom.
Add the counts: 1 + 1 = 2.
So one NaCl particle holds 2 atoms.

Q10bare

The sharp gas from a struck match is sulfur dioxide, SO₂. How many atoms in all does one SO₂ particle hold?

Typed answer

Answer

Accepted: 3 · 3 atoms · three

S has no subscript: 1 sulfur atom. The 2 after the O: 2 oxygen atoms.
Add the counts: 1 + 2 = 3.
So one SO₂ particle holds 3 atoms.

Q11bare

Ethanol, the alcohol in many hand sanitizers, is C₂H₆O. How many hydrogen atoms does one C₂H₆O particle hold?

Typed answer

Answer

Accepted: 6 · 6 hydrogen atoms · six · 6 atoms

The subscript after the H is 6.
So one C₂H₆O particle holds 6 hydrogen atoms.

Q12bare

The acid in a car battery is H₂SO₄. How many atoms in all does one H₂SO₄ particle hold?

Typed answer

Answer

Accepted: 7 · 7 atoms · seven

H₂: 2 hydrogen atoms. S with no subscript: 1 sulfur atom. O₄: 4 oxygen atoms.
Add the counts: 2 + 1 + 4 = 7.
So one H₂SO₄ particle holds 7 atoms.

Q13misconception

Kofi says: "One particle of H₂O₂ holds 2 atoms." Is Kofi correct?

A yes
B no

Answer

Key: B — no

The 2 after the H counts 2 hydrogen atoms.
The 2 after the O counts 2 oxygen atoms.
Add the counts: 2 + 2 = 4 atoms, so Kofi is not correct.

Feedback per option

A The 2 after the H is 2 hydrogen atoms and the 2 after the O is 2 oxygen atoms: 4 atoms in all, not 2.
B Count each element: 2 hydrogen atoms and 2 oxygen atoms, so one H₂O₂ particle holds 4 atoms.

Your note · lesson 2: Count the atoms in a formula

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 3 of 5Author: definitely a video199 words · about 1:40

Change a subscript, change the substance

MAT-059b · Changing a subscript changes the substance — Explain why changing a subscript in a chemical formula produces a different substance.

Script

Say	Screen
H₂O is water, and you drink it.	[a glass of water; H₂O beside its particle]
H₂O₂ is hydrogen peroxide: it bleaches hair and stings in a cut.	[a brown bottle; H₂O₂ beside its particle]
The two formulas differ by one small 2: why does one small number make a different substance?	[the two formulas; the extra 2 glows; question mark]
Because the 2 builds a different particle.	[the two particles side by side]
A subscript counts the atoms in one particle.	[H₂O: the 2 boxed; its particle]
Count H₂O: 2 hydrogen atoms and 1 oxygen atom, 3 atoms.	[the water particle; counts appear]
Now compare the hydrogen peroxide particle, drawn beside the water particle: the peroxide particle holds one more oxygen atom.	[the two particles side by side, H₂O under the left and H₂O₂ under the right; the extra large open circle in the right particle ringed; nothing moves between them]
Count H₂O₂: 2 hydrogen atoms and 2 oxygen atoms, 4 atoms: a different particle.	[the extra oxygen ringed; counts appear]
A substance's properties come from its particles, so a different particle is a different substance.	[labels under the two particles: WATER on the left, HYDROGEN PEROXIDE on the right]
H₂O₂ is not water with extra oxygen mixed in; hydrogen peroxide is its own substance.	[the two particles side by side; the property table]
Now consider CO, a poisonous gas, and CO₂, the gas you breathe out.	[CO and CO₂ beside their particles]
The CO₂ particle holds one more oxygen atom: a different particle, so a different substance.	[the extra oxygen ringed; the two property rows]
So, change a subscript, and you have built a different particle.	[the rule slide: the water and peroxide particles side by side with their labels; nothing else printed]
And a different particle is a different substance.	[the two labels glow in turn]
So the two bottles are one small 2 apart, and you drink one while the other bleaches hair.	[the glass and the brown bottle]
Okay, now your turn.	[closing screen: bullets — • Change a subscript, and you have built a different particle • A different particle is a different substance]

“Okay, now your turn.” — the attached question

video

A particle holds 2 hydrogen atoms and 2 oxygen atoms: H₂O₂. What substance is it?

A water
B hydrogen peroxide
C oxygen gas

Answer

Key: B — hydrogen peroxide

H₂O₂ is a different particle from H₂O.
A different particle is a different substance.
H₂O₂ is hydrogen peroxide.

Feedback per option

A Water is H₂O: 2 hydrogen atoms and 1 oxygen atom. A particle with one more oxygen atom is a different particle.
B H₂O₂ is a different particle from H₂O, so it is a different substance: hydrogen peroxide.
C Oxygen gas is O₂; this particle holds 2 hydrogen atoms as well.

Quiz after the video — the mastery check, 10 items

Q1recall

In a chemical formula, what does a subscript count?

A the particles in a sample
B the atoms of the element just before it
C the elements in the particle

Answer

Key: B — the atoms of the element just before it

A subscript is written just after a symbol.
It counts that element's atoms in one particle.
So a subscript counts the atoms of the element just before it.

Feedback per option

A A subscript counts atoms in one particle, not particles in a sample.
B A subscript counts the atoms of the element whose symbol comes just before it.
C The symbols name the elements; the subscript counts one element's atoms.

Q2recall

Table salt is a compound of sodium and chlorine. Whose properties does table salt have?

A its own properties
B sodium's properties
C chlorine's properties

Answer

Key: A — its own properties

A compound's particles are new particles.
A substance's properties come from its particles.
So table salt has its own properties, not sodium's or chlorine's.

Feedback per option

A A compound's particles are new particles, so a compound has its own properties.
B Sodium is a soft metal that fizzes in water; table salt is neither, because its particles are new particles.
C Chlorine is a poisonous green gas; table salt is safe to eat, because its particles are new particles.

Q3what

Is H₂O₂ water?

A yes
B no

Answer

Key: B — no

Water's particles are H₂O.
The H₂O₂ particle holds one more oxygen atom, so it is a different particle.
A different particle is a different substance, so H₂O₂ is not water.

Feedback per option

A Water is H₂O. The H₂O₂ particle holds one more oxygen atom, so it is a different particle and a different substance.
B The H₂O₂ particle holds 2 oxygen atoms and the water particle holds 1, so H₂O₂ is a different substance: hydrogen peroxide.

Q4what

In this drawing, light gray circles are nitrogen atoms, large open circles are oxygen atoms, and touching circles are joined. Do particle 1 and particle 2 show the same substance?

A yes
B no

Answer

Key: B — no

Count particle 1: 2 light gray circles and 1 large open circle, so 2 nitrogen atoms and 1 oxygen atom.
Count particle 2: 1 nitrogen atom and 2 oxygen atoms.
The particles differ, so the substances differ.

Feedback per option

A Particle 1 holds 2 nitrogen atoms and 1 oxygen atom; particle 2 holds 1 nitrogen atom and 2 oxygen atoms. Different particles, different substances.
B The counts differ: particle 1 has 2 nitrogen atoms and 1 oxygen atom, particle 2 has 1 nitrogen atom and 2 oxygen atoms, so they are different substances.

Q5why

O₂ is the oxygen gas you breathe, and O₃ is ozone, a gas that is poisonous to breathe. Both formulas hold only oxygen atoms. Explain why ozone is a different substance from oxygen gas.

Starter: A subscript counts…

Answer

Model answer · ['a subscript counts the atoms in one particle: 2 oxygen atoms against 3', 'so the O₃ particle is a different particle', "a substance's properties come from its particles, so ozone is a different substance"] points

A subscript counts the atoms in one particle.
An O₂ particle holds 2 oxygen atoms, and an O₃ particle holds 3 oxygen atoms.
So the O₃ particle is a different particle.
A substance's properties come from its particles.
So ozone is a different substance from oxygen gas, with its own properties.

Q6misconception

Anouk says: "H₂O₂ is just water with a bit more oxygen mixed in." Is Anouk correct?

A yes
B no

Answer

Key: B — no

In H₂O₂ the second oxygen atom is joined into the particle, not mixed into the liquid.
So the H₂O₂ particle is a different particle from the water particle.
A different particle is a different substance, so Anouk is not correct.

Feedback per option

A Nothing is mixed in: the extra oxygen atom is joined into the particle itself, so the particle is a different particle.
B The extra oxygen atom is joined into the H₂O₂ particle, so the particle is different and the substance is different.

Q7transfer

NO and NO₂ are two gases. Are NO and NO₂ different substances or the same substance?

A different substances
B the same substance

Answer

Key: A — different substances

Count the oxygen atoms: 1 in NO, 2 in NO₂.
So the two particles are different particles.
A different particle is a different substance.

Feedback per option

A The NO₂ particle holds 2 oxygen atoms and the NO particle holds 1: different particles, so different substances.
B The NO₂ particle holds one more oxygen atom than the NO particle, so it is a different particle and a different substance.

Q8transfer

SO₂ and SO₃ are two compounds of sulfur and oxygen whose formulas differ by one subscript. Which statement is correct?

A They are different substances, each with its own properties.
B They are the same substance, one a little richer in oxygen.

Answer

Key: A — They are different substances, each with its own properties.

The subscripts differ: 2 oxygen atoms in SO₂, 3 oxygen atoms in SO₃.
So the two particles are different particles.
A different particle is a different substance, with its own properties.

Feedback per option

A The SO₃ particle holds 3 oxygen atoms and the SO₂ particle holds 2: different particles, so different substances with their own properties.
B A changed subscript builds a different particle, not a richer version of the same one; the substances differ.

Q9misconception

Milo says: "CO and CO₂ are different substances, because their particles are different." Is Milo correct?

A yes
B no

Answer

Key: A — yes

The CO particle holds 1 oxygen atom, and the CO₂ particle holds 2 oxygen atoms.
So the two particles are different particles.
A different particle is a different substance, so Milo is correct.

Feedback per option

A The CO₂ particle holds one more oxygen atom than the CO particle; a different particle is a different substance, as Milo says.
B The CO particle holds 1 oxygen atom and the CO₂ particle holds 2, so the particles differ, and a different particle is a different substance.

Q10transfer

Ethane, C₂H₆, is a gas in natural gas. Ethene, C₂H₄, is the gas that ripens fruit. How many fewer hydrogen atoms does one ethene particle hold than one ethane particle?

Typed answer

Answer

Accepted: 2 · 2 hydrogen atoms · two · 2 atoms · 2 fewer

The subscript after the H is 6 in C₂H₆ and 4 in C₂H₄.
6 − 4 = 2.
So one ethene particle holds 2 fewer hydrogen atoms, and that makes it a different substance.

Your note · lesson 3: Change a subscript, change the substance

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 4 of 5Author: could do without a video197 words · about 1:38

A number in front: coefficients

MAT-061 · Count atoms when a formula has coefficients or parentheses — Count the number of atoms of each element in a formula that includes a coefficient, parentheses, or both.

Script

Say	Screen
Two water particles sit side by side, and chemists want to write the two particles, not one.	[two water particles; H₂O under the first]
You cannot change the subscripts: a changed subscript builds a different particle, not water.	[the subscript 2 glows; the subscripts doubled, H₄O₂, appear under the two particles and are crossed out: a different particle, not two waters]
So how do you write two water particles?	[question mark]
Chemists write a full-size number in front of the formula: 2H₂O.	[a large 2 slides in front of H₂O]
A full-size number written in front of a formula is called a coefficient, and it counts whole particles.	[chip: COEFFICIENT; the 2 boxed; the two particles ringed]
A subscript counts the atoms in one particle: one water particle holds 2 hydrogen atoms and 1 oxygen atom.	[one particle; counts 2 and 1]
So two particles hold 4 hydrogen atoms and 2 oxygen atoms.	[table: one particle 2, 1; two particles 4, 2]
So a coefficient multiplies every count in the formula: 6 atoms in all.	[total row: 6]
Now consider three carbon dioxide particles, written 3CO₂.	[three CO₂ particles; 3CO₂ under them, the 3 boxed]
Three times 1 carbon atom is 3 carbon atoms, and three times 2 oxygen atoms is 6 oxygen atoms: 9 atoms in all.	[table fills: 3, 6, total 9]
There are two different 2s: the full-size 2 in front counts particles, and the small, low 2 after the H counts hydrogen atoms.	[2H₂O with both 2s boxed and labeled]
So, a coefficient counts whole particles, and it multiplies every count in the formula.	[the rule slide: 2H₂O and its table; chip COEFFICIENT; nothing else printed]
So two water particles are written 2H₂O, with 6 atoms in all.	[the two particles; 2H₂O]
Okay, now your turn.	[closing screen: one line — "A coefficient counts whole particles, and it multiplies every count in the formula."]

“Okay, now your turn.” — the attached question

video

Two water particles are written 2H₂O. How many atoms are there in all?

Answer

Key: B — 6

One water particle holds 2 hydrogen atoms and 1 oxygen atom: 3 atoms.
The coefficient 2 means two particles, so multiply: 2 × 3 = 6.
So 2H₂O holds 6 atoms in all.

Feedback per option

A 3 is the atoms in ONE water particle; multiply by the coefficient 2.
B One water particle holds 3 atoms, and two particles hold 2 × 3 = 6 atoms.
C 9 would be three water particles; the coefficient is 2.

Quiz after the video — the mastery check, 14 items

Q1recall

How many oxygen atoms does ONE particle of SO₂ hold?

A 1 oxygen atom
B 2 oxygen atoms
C 3 oxygen atoms

Answer

Key: B — 2 oxygen atoms

The subscript after the O is 2.
A subscript counts the atoms of the element just before it.
So one SO₂ particle holds 2 oxygen atoms.

Feedback per option

A The S has no subscript, so 1 sulfur atom; the 2 after the O counts oxygen atoms.
B The subscript after the O is 2, so one SO₂ particle holds 2 oxygen atoms.
C 3 is the total of all the atoms; the oxygen atoms alone are 2.

Q2term

In 3CO₂, the 3 is a full-size number written in front of the formula. What is a number written like this called?

Typed answer

Answer

Accepted: coefficient · a coefficient · the coefficient

The 3 sits in front of the formula, at full size, on the line.
A full-size number written in front of a formula is called a coefficient.

Q3fluency

In 2SO₂, what does the full-size 2 in front count?

A particles
B atoms

Answer

Key: A — particles

The 2 in front is full size and sits in front of the formula.
A number in front is a coefficient, and a coefficient counts whole particles.
So the 2 in front counts two SO₂ particles.

Feedback per option

A A full-size number in front is a coefficient, and a coefficient counts whole particles: two SO₂ particles.
B The number in front counts particles; only a subscript counts atoms.

Q4fluency

In 2SO₂, what does the small 2 count?

A particles
B atoms
C elements

Answer

Key: B — atoms

The small 2 is written low, just after the O.
A small number written low after a symbol is a subscript, and a subscript counts atoms.
So the small 2 counts 2 oxygen atoms.

Feedback per option

A The small, low 2 is a subscript, and a subscript counts atoms: 2 oxygen atoms in one particle.
B The 2 is written small and low after the O, so it is a subscript: 2 oxygen atoms in one particle.
C The symbols S and O name the elements; the small, low 2 is a subscript, and a subscript counts atoms: 2 oxygen atoms in one particle.

Q5fluency

In 5O₂, what does the small 2 count?

A particles
B atoms

Answer

Key: B — atoms

The 2 is written small and low, just after the O.
A subscript counts atoms.
So the 2 counts 2 oxygen atoms in one particle.

Feedback per option

A The small, low 2 after the O is a subscript, and a subscript counts atoms: 2 oxygen atoms in one particle.
B The 2 is written small and low after the O, so it is a subscript: 2 oxygen atoms in one particle.

Q6fluency

In 3CH₄, what does the 3 in front count?

A particles
B atoms

Answer

Key: A — particles

The 3 is full size and sits in front of the formula.
A coefficient counts whole particles.
So the 3 counts three CH₄ particles.

Feedback per option

A A full-size number in front is a coefficient, and a coefficient counts whole particles: three CH₄ particles.
B The number in front counts particles; the small 4 is the one that counts atoms.

Q7scaffold

Ammonia is NH₃. A chemist writes 4NH₃. How many hydrogen atoms does ONE NH₃ particle hold?

Typed answer

Answer

Accepted: 3 · 3 hydrogen atoms · three · 3 atoms

The subscript after the H is 3.
So one NH₃ particle holds 3 hydrogen atoms.

Q8scaffold

In 4NH₃, read the coefficient. How many NH₃ particles does 4NH₃ mean?

Typed answer

Answer

Accepted: 4 · 4 particles · four

The 4 in front is the coefficient.
A coefficient counts whole particles.
So 4NH₃ means four NH₃ particles.

Q9scaffold

Multiply your two answers for 4NH₃ together. How many hydrogen atoms does 4NH₃ hold in all?

Typed answer

Answer

Accepted: 12 · 12 hydrogen atoms · twelve · 12 atoms

One NH₃ particle holds 3 hydrogen atoms.
4NH₃ is four particles, so multiply: 4 × 3 = 12.
So 4NH₃ holds 12 hydrogen atoms in all.

Q10bare

How many oxygen atoms does 5O₂ hold in all?

Typed answer

Answer

Accepted: 10 · 10 oxygen atoms · ten · 10 atoms

One O₂ particle holds 2 oxygen atoms.
The coefficient 5 means five particles: 5 × 2 = 10.
So 5O₂ holds 10 oxygen atoms in all.

Q11bare

Glucose is C₆H₁₂O₆. How many carbon atoms does 2C₆H₁₂O₆ hold in all?

Typed answer

Answer

Accepted: 12 · 12 carbon atoms · twelve · 12 atoms

One glucose particle holds 6 carbon atoms.
The coefficient 2 means two particles: 2 × 6 = 12.
So 2C₆H₁₂O₆ holds 12 carbon atoms in all.

Q12bare

Methane, the main gas in natural gas, is CH₄. How many atoms in all does 3CH₄ hold?

Typed answer

Answer

Accepted: 15 · 15 atoms · fifteen · 15 atoms in all

One CH₄ particle holds 1 carbon atom and 4 hydrogen atoms: 5 atoms.
The coefficient 3 means three particles: 3 × 5 = 15.
So 3CH₄ holds 15 atoms in all.

Q13transfer

Touching circles are joined. In this drawing, gray circles are carbon atoms and large open circles are oxygen atoms. Which line writes what is drawn?

A 3CO
B CO₃
C C₃O₃

Answer

Key: A — 3CO

The drawing shows three separate particles, each 1 gray circle joined to 1 large open circle.
Each particle is CO.
Three whole particles take a coefficient of 3: 3CO.

Feedback per option

A Three identical particles, each 1 carbon atom joined to 1 oxygen atom: a coefficient 3 in front of CO.
B CO₃ would be ONE particle of 1 carbon atom and 3 oxygen atoms; the drawing shows three separate particles.
C C₃O₃ would be ONE particle of 6 atoms joined; the drawing shows three separate two-atom particles.

Q14misconception

Esme says: "3H₂O holds 3 + 2 = 5 hydrogen atoms and 3 + 1 = 4 oxygen atoms." Is Esme correct?

A yes
B no

Answer

Key: B — no

A coefficient multiplies every count in the formula.
Hydrogen: 3 × 2 = 6 hydrogen atoms, not 5.
Oxygen: 3 × 1 = 3 oxygen atoms, not 4, so Esme is not correct.

Feedback per option

A A coefficient multiplies every count: 3 × 2 = 6 hydrogen atoms and 3 × 1 = 3 oxygen atoms; adding gives the wrong counts.
B Three water particles hold 3 × 2 = 6 hydrogen atoms and 3 × 1 = 3 oxygen atoms; Esme added instead of multiplying.

Your note · lesson 4: A number in front: coefficients

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Lesson 5 of 5Author: could do without a video199 words · about 1:40

Parentheses: a group repeated

MAT-061 · Count atoms when a formula has coefficients or parentheses — Count the number of atoms of each element in a formula that includes a coefficient, parentheses, or both.

Script

Say	Screen
The medicine in milk of magnesia is magnesium hydroxide, Mg(OH)₂.	[the medicine bottle; Mg(OH)₂ large]
Parentheses wrap the O and the H, and a small 2 follows the closing parenthesis.	[the parentheses glow; the 2 boxed]
What does that 2 count?	[question mark]
It repeats the whole group inside the parentheses.	[the OH group ringed twice]
A subscript counts the element just before it, and a coefficient counts whole particles.	[H₂O with its 2 boxed; 2H₂O with its 2 boxed]
The parentheses hold a group of atoms: one oxygen atom and one hydrogen atom.	[the OH group ringed on the particle]
The 2 comes just after the group, so it repeats the whole group: two OH groups.	[a second OH group appears; both ringed]
So Mg(OH)₂ holds 1 magnesium atom, 2 oxygen atoms and 2 hydrogen atoms: 5 atoms in one particle.	[the counting table fills; total 5]
Now consider Al(OH)₃: the 3 repeats the OH group three times: 1 aluminum atom, 3 oxygen atoms and 3 hydrogen atoms, so 7 atoms in all.	[Al(OH)₃ beside its particle; the three OH groups ringed; table fills: 1, 3, 3, total 7]
With a coefficient in front, as in 2Mg(OH)₂, count one particle first, parentheses and all.	[two particles; 2Mg(OH)₂; the one-particle column: 1, 2, 2]
Then multiply every count by the coefficient: 2 magnesium atoms, 4 oxygen atoms and 4 hydrogen atoms: 10 atoms.	[the two-particle column: 2, 4, 4; total 10]
So, a subscript after a closing parenthesis repeats the whole group inside the parentheses.	[the rule slide: the Mg(OH)₂ particle with both OH groups ringed and its table; nothing else printed]
When a coefficient sits in front, count one particle first, then multiply every count by the coefficient.	[the two-column table]
Okay, now your turn.	[closing screen: bullets — • A subscript after a closing parenthesis repeats the whole group inside • With a coefficient in front, count one particle first, then multiply every count]

“Okay, now your turn.” — the attached question

video

Magnesium hydroxide is written Mg(OH)₂. What does the 2 after the closing parenthesis repeat?

A the whole OH group
B only the H
C the Mg

Answer

Key: A — the whole OH group

The 2 comes just after the closing parenthesis.
A subscript after a closing parenthesis repeats the whole group inside.
So the 2 repeats the whole OH group.

Feedback per option

A The 2 comes after the closing parenthesis, so it repeats everything inside: two OH groups.
B The 2 sits after the parenthesis, not just after the H, so it repeats the whole group.
C Mg sits outside the parentheses; the 2 repeats only what is inside them.

Quiz after the video — the mastery check, 14 items

Q1recall

How many oxygen atoms does ONE particle of SO₃ hold?

A 1 oxygen atom
B 3 oxygen atoms
C 4 oxygen atoms

Answer

Key: B — 3 oxygen atoms

The subscript after the O is 3.
A subscript counts the atoms of the element just before it.
So one SO₃ particle holds 3 oxygen atoms.

Feedback per option

A The S has no subscript, so 1 sulfur atom; the 3 after the O counts oxygen atoms.
B The subscript after the O is 3, so one SO₃ particle holds 3 oxygen atoms.
C 4 is the total of all the atoms; the oxygen atoms alone are 3.

Q2recall

In 4CO₂, what does the 4 in front count?

A whole particles
B carbon atoms
C oxygen atoms

Answer

Key: A — whole particles

The 4 is full size and sits in front of the formula.
A number written like that is a coefficient.
A coefficient counts whole particles: four CO₂ particles.

Feedback per option

A A full-size number in front is a coefficient, and a coefficient counts whole particles: four CO₂ particles.
B The carbon count is the C with no subscript: 1 carbon atom in each particle. The 4 in front counts particles.
C The oxygen count is the subscript 2. The 4 in front counts particles.

Q3scaffold

Calcium nitrate, a fertilizer, is Ca(NO₃)₂. In the drawing, the large dark circle is calcium, light gray circles are nitrogen, large open circles are oxygen, and touching circles are joined. What does ONE group inside the parentheses hold?

A 1 nitrogen atom and 1 oxygen atom
B 1 nitrogen atom and 3 oxygen atoms
C 3 nitrogen atoms and 3 oxygen atoms

Answer

Key: B — 1 nitrogen atom and 3 oxygen atoms

Read inside the parentheses: N and O₃.
N has no subscript: 1 nitrogen atom. The 3 after the O: 3 oxygen atoms.
So one group holds 1 nitrogen atom and 3 oxygen atoms.

Feedback per option

A The 3 after the O is inside the parentheses, so one group holds 3 oxygen atoms, not 1.
B Inside the parentheses: N with no subscript, 1 nitrogen atom, and O₃, 3 oxygen atoms. In the drawing, each light gray circle carries three large open circles.
C The 3 comes just after the O, so it counts oxygen atoms only; the N has no subscript: 1 nitrogen atom.

Q4scaffold

In Ca(NO₃)₂, the 2 after the closing parenthesis repeats the group. How many oxygen atoms does one Ca(NO₃)₂ particle hold?

Typed answer

Answer

Accepted: 6 · 6 oxygen atoms · six · 6 atoms

One group holds 3 oxygen atoms.
The 2 after the parentheses repeats the group: 2 × 3 = 6.
So one Ca(NO₃)₂ particle holds 6 oxygen atoms.

Q5scaffold

In Ca(NO₃)₂, how many nitrogen atoms does one particle hold?

Typed answer

Answer

Accepted: 2 · 2 nitrogen atoms · two · 2 atoms

One group holds 1 nitrogen atom.
The 2 after the parentheses repeats the group: 2 × 1 = 2.
So one Ca(NO₃)₂ particle holds 2 nitrogen atoms.

Q6scaffold

Ca has no subscript: 1 calcium atom. Now add your calcium, nitrogen and oxygen counts. How many atoms in all does one Ca(NO₃)₂ particle hold?

Typed answer

Answer

Accepted: 9 · 9 atoms · nine · 9 atoms in all

Ca has no subscript: 1 calcium atom.
Nitrogen: 2 atoms. Oxygen: 6 atoms.
Add the counts: 1 + 2 + 6 = 9 atoms.

Q7bare

Copper hydroxide, a blue solid, is Cu(OH)₂. How many hydrogen atoms does one Cu(OH)₂ particle hold?

Typed answer

Answer

Accepted: 2 · 2 hydrogen atoms · two · 2 atoms

Inside the parentheses, 1 hydrogen atom.
The 2 after the parentheses repeats the group: 2 × 1 = 2.
So one Cu(OH)₂ particle holds 2 hydrogen atoms.

Q8bare

The green color in some fireworks comes from barium nitrate, Ba(NO₃)₂. How many oxygen atoms does one Ba(NO₃)₂ particle hold?

Typed answer

Answer

Accepted: 6 · 6 oxygen atoms · six · 6 atoms

Inside the parentheses, 3 oxygen atoms.
The 2 after the parentheses repeats the group: 2 × 3 = 6.
So one Ba(NO₃)₂ particle holds 6 oxygen atoms.

Q9bare

Calcium phosphate, Ca₃(PO₄)₂, is a close relative of the hard mineral in bones and teeth. How many atoms in all does one Ca₃(PO₄)₂ particle hold?

Typed answer

Answer

Accepted: 13 · 13 atoms · thirteen · 13 atoms in all

Ca₃: 3 calcium atoms.
Inside the parentheses, 1 phosphorus atom and 4 oxygen atoms, repeated 2 times: 2 phosphorus atoms and 8 oxygen atoms.
Add the counts: 3 + 2 + 8 = 13 atoms.

Q10misconception

Callum says: "In Mg(OH)₂, the 2 counts only the hydrogen atoms, because the H is the letter just before it." Is Callum correct?

A yes
B no

Answer

Key: B — no

The 2 comes just after the closing parenthesis, not just after the H.
A subscript after a closing parenthesis repeats the whole group inside.
So the 2 counts 2 oxygen atoms and 2 hydrogen atoms, and Callum is not correct.

Feedback per option

A The 2 comes after the closing parenthesis, so it repeats everything inside the parentheses, not the H alone.
B The 2 sits after the closing parenthesis, so it repeats the whole OH group: 2 oxygen atoms and 2 hydrogen atoms.

Q11scaffold

Calcium hypochlorite, the powder called pool chlorine, is Ca(ClO)₂. A chemist writes 3Ca(ClO)₂. Count one particle first: how many oxygen atoms does ONE Ca(ClO)₂ particle hold?

Typed answer

Answer

Accepted: 2 · 2 oxygen atoms · two · 2 atoms

Inside the parentheses, 1 oxygen atom.
The 2 after the parentheses repeats the group: 2 × 1 = 2.
So one Ca(ClO)₂ particle holds 2 oxygen atoms.

Q12scaffold

Now multiply your one-particle count by the coefficient. How many oxygen atoms does 3Ca(ClO)₂ hold in all?

Typed answer

Answer

Accepted: 6 · 6 oxygen atoms · six · 6 atoms

One Ca(ClO)₂ particle holds 2 oxygen atoms.
The coefficient 3 means three particles: 3 × 2 = 6.
So 3Ca(ClO)₂ holds 6 oxygen atoms in all.

Q13bare

How many oxygen atoms does 3Ba(NO₃)₂ hold in all?

Typed answer

Answer

Accepted: 18 · 18 oxygen atoms · eighteen · 18 atoms

One Ba(NO₃)₂ particle: 3 oxygen atoms inside the parentheses × 2 = 6 oxygen atoms.
The coefficient 3 means three particles: 3 × 6 = 18.
So 3Ba(NO₃)₂ holds 18 oxygen atoms in all.

Q14bare

Zinc hydroxide is Zn(OH)₂. How many atoms in all does 2Zn(OH)₂ hold?

Typed answer

Answer

Accepted: 10 · 10 atoms · ten · 10 atoms in all

One Zn(OH)₂ particle: 1 zinc atom, 2 oxygen atoms, 2 hydrogen atoms, 5 atoms.
The coefficient 2 means two particles: 2 × 5 = 10.
So 2Zn(OH)₂ holds 10 atoms in all.

Your note · lesson 5: Parentheses: a group repeated

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Summary video · everything taught, in order, just before the PP100210 words · about 1:45

Summary: Chemical formulas

Script, part 1 (110 words)

Say	Screen
Here is everything we found out about chemical formulas.	[a still: H₂O beside its particle]
Every element has a chemical symbol of one or two letters: the first a capital, the second small.	[H, O, Na, Cl]
A chemical formula writes one particle of a substance.	[H₂O beside its particle]
Each symbol names one element in the particle.	[H and O ringed]
A small number written low after a symbol is called a subscript.	[the 2 boxed; chip: SUBSCRIPT]
A subscript counts the atoms of the element just before it, in one particle.	[the two hydrogen atoms ringed]
A symbol with no subscript counts one atom.	[the O; label: 1 oxygen atom]
To count the atoms in a formula, take the symbols one at a time, read each subscript as that element's count, and add the counts for the total.	[the glucose counting table]
Okay, now your turn.	[closing screen: bullets — • A chemical formula writes one particle • Each symbol names one element • A subscript counts the atoms of the element just before it • No subscript: one atom]

“Okay, now your turn.” — the check question between the parts

video

Methane is CH₄. How many hydrogen atoms are in one methane particle?

Answer

Key: B — 4

A subscript counts the atoms of the element just before it.
The 4 comes after the H.
So one methane particle holds 4 hydrogen atoms.

Feedback per option

A 1 is the carbon count: the C has no subscript.
B The 4 after the H counts 4 hydrogen atoms.
C 5 is the total of all the atoms; the hydrogen atoms alone are 4.

Script, part 2 (100 words)

Say	Screen
Here is everything we found out about changing the numbers in a formula.	[a still: H₂O and H₂O₂ beside their particles]
Change a subscript, and you have built a different particle.	[H₂O becomes H₂O₂]
A substance's properties come from its particles, so a different particle is a different substance.	[the labels WATER and HYDROGEN PEROXIDE]
A full-size number in front of a formula is called a coefficient, and it counts whole particles.	[2H₂O; the 2 boxed; two particles; chip: COEFFICIENT]
A coefficient multiplies every count in the formula.	[the 2H₂O counting table]
A subscript after a closing parenthesis repeats the whole group inside the parentheses.	[Mg(OH)₂ beside its particle; both OH groups ringed]
And when a coefficient sits in front as well, count one particle first, then multiply every count by the coefficient.	[2Mg(OH)₂; the two-column table]
Okay, now your turn.	[closing screen: bullets — • Change a subscript: a different particle, a different substance • A coefficient counts whole particles and multiplies every count • A subscript after a closing parenthesis repeats the whole group]

“Okay, now your turn.” — the two questions after part 2

video

In 2H₂O, which number counts whole water particles?

A the small 2 after the H
B both of them
C the full-size 2 in front

Answer

Key: C — the full-size 2 in front

A full-size number in front of a formula is called a coefficient.
A coefficient counts whole particles.
So the full-size 2 counts two water particles.

Feedback per option

A The small, low 2 after the H is a subscript: it counts hydrogen atoms in one particle.
B Only the full-size 2 in front counts particles; the small 2 counts hydrogen atoms.
C The full-size number in front is the coefficient, and it counts whole particles.

video

Two particles of magnesium hydroxide are written 2Mg(OH)₂. How many oxygen atoms are there in all?

Answer

Key: C — 4

The 2 after the parentheses repeats the OH group: 2 oxygen atoms in one particle.
The coefficient 2 means two particles: 2 × 2 = 4.
So 2Mg(OH)₂ holds 4 oxygen atoms in all.

Feedback per option

A 1 is the oxygen count inside the parentheses; the 2 after them repeats it, and the coefficient doubles that.
B 2 is the oxygen count in ONE particle; the coefficient 2 doubles it.
C One particle: 2 oxygen atoms. Two particles: 2 × 2 = 4 oxygen atoms.

Your note · the summary video

What to judge

Is this content better than the current alternative students have (PhysicsGraph / Edmentum)?

8/10 on:

Clear and concise language
Physics accuracy (read as chemistry accuracy here; his line as pasted for HS Physics)
No "clangers" (content that causes a problematic misconception)
Appropriate questions
Initial testing
Expansion into harder questions (no exam)
The tasks should use similar language to that of the lesson

Gut check: better than the alternative? Would a student benefit? Full criteria

Applied without asking

Rulings you have already given; in force on every card above, not re-asked.

Every video ends “Okay, now your turn.” with one easy, video-dependent question (the XP gate).
An intro video is at most 120 words and teaches nothing: it opens the question the topic answers.
A summary video is at most 300 words: everything taught, in order, just before the PP100.
A lesson script is at most 200 words.
Each lesson ships as both a video and an article; the article is not under review here.

The topic’s fixed wording (the lexicon the scripts repeat)

Every element has a chemical symbol of one or two letters: the first a capital, the second small.
A substance made of two or more kinds of atom joined together in a fixed pattern is called a compound.
Two or more atoms joined together make one particle called a molecule.
A compound's particles are new particles, so a compound has its own properties.
A chemical formula writes one particle of a substance.
Each symbol names one element in the particle.
A small number written low after a symbol is called a subscript.
A subscript counts the atoms of the element just before it, in one particle.
A symbol with no subscript counts one atom.
To count the atoms in a formula, take the symbols one at a time, read each subscript as that element's count, and add the counts for the total.
Change a subscript, and you have built a different particle.
A substance's properties come from its particles, so a different particle is a different substance.
A full-size number in front of a formula is called a coefficient, and it counts whole particles.
A coefficient multiplies every count in the formula.
A subscript after a closing parenthesis repeats the whole group inside the parentheses.

Scripts, questions and quizzes are read from the course content as it stands today; the student site for this topic is here.