Atoms, elements, compounds and formulae
Chemistry has a written language. Get formulae right at KS3 and GCSE equations become bookkeeping rather than guesswork.
Lesson overview
What you'll learn in this lesson
Understand atoms, elements and compounds, and the use of chemical symbols and formulae
Key learning points
- • Symbols are not abbreviations
- • Counting atoms in a formula
- • Compounds have new properties
- • Mixtures can be separated physically
This lesson at a glance
- 30 minutes
- 25 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 25
Visual introductionPicture this
Atoms, elements, compounds and formulae
Chemistry has a written language. Get formulae right at KS3 and GCSE equations become bookkeeping rather than guesswork.
In a nutshell
Understand atoms, elements and compounds, and the use of chemical symbols and formulae
What you already know
Part 2 of 25
Before we start
What you already know
You should already know that matter is made of particles and that the periodic table lists elements.
Key words
Part 3 of 25
Key words
Words you'll need today
- Element
- A substance made of only one type of atom.
- Compound
- Two or more elements chemically bonded in fixed proportions.
- Mixture
- Substances together but not chemically joined.
- Formula
- Symbols and numbers showing the atoms in a substance.
- Subscript
- The small number showing how many atoms of the element before it.
Reset break
Part 4 of 25
Pause
That's sitting 1 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 5 of 25
Learning cycle 1 of 2
Reading the symbols
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 25
Learn
Symbols are not abbreviations
Each element has an agreed one- or two-letter symbol, with the second letter always lower case. CO is carbon monoxide, a compound; Co is cobalt, an element. That capital letter carries real information.
Explore the idea
Part 7 of 25
Learn
Counting atoms in a formula
In H2SO4 there are two hydrogen, one sulfur and four oxygen atoms. Brackets multiply everything inside: Ca(OH)2 has one calcium, two oxygen and two hydrogen. A big number in front multiplies the whole formula: 3H2O is six hydrogen and three oxygen atoms.
Reset break
Part 8 of 25
Pause
That's sitting 2 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 9 of 25
Quick check
Part 10 of 25
Learning cycle
Part 11 of 25
Learning cycle 2 of 2
Compounds versus mixtures
A short piece of teaching, then a check to make sure it has landed.
Reset break
Part 12 of 25
Pause
That's sitting 3 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 13 of 25
Learn
Compounds have new properties
Sodium is a reactive metal and chlorine a toxic gas, yet sodium chloride is table salt. A compound's properties are not the average of its elements, because bonding has changed the arrangement of the outer electrons.
Explore the idea
Part 14 of 25
Learn
Mixtures can be separated physically
Air, sea water and steel are mixtures: their components keep their properties and can be separated by filtration, distillation or chromatography. Splitting a compound needs a chemical reaction, usually a lot more energy.
Quick check
Part 15 of 25
Reset break
Part 16 of 25
Pause
That's sitting 4 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 17 of 25
Common mix-ups
Part 18 of 25
Common mix-ups
Things people often get wrong
- CO and Co are not the same thing — capitalisation matters.
- A compound is not a mixture: its proportions are fixed.
- The big number in front multiplies every atom in the formula, including those in brackets.
Challenge round
Part 19 of 25
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 20 of 25
Pause
That's sitting 5 of 6 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 21 of 25
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
A compound's properties are not the average of its ____, because bonding has changed the arrangement of the outer electrons.
Splitting a compound needs a ____ reaction, usually a lot more energy.
Challenge round
Part 22 of 25
Game · Recall cards
How many atoms in total are in H2SO4?
Card 1 of 4
Exit quiz
Part 23 of 25
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. An element contains...
2. Co is...
3. Separating a compound needs...
4. Sodium chloride's properties are...
5. Subscripts apply to...
6. Steel is best described as...
Mastery quiz
Part 24 of 25
Marked quiz
End of lesson quiz: Atoms, elements, compounds and formulae
4 questions, marked with the reasoning shown. No timer.
1. How many atoms in total are in H2SO4?
2. Ca(OH)2 contains how many hydrogen atoms?
3. Which is a mixture?
4. 3H2O contains how many oxygen atoms?
Lesson round-up
Part 25 of 25
Lesson round-up
Ready when you are
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Ask LunaPart 1 of 25 · Watch & discover