Atoms, elements and compounds
All matter is built from around a hundred kinds of atom. Chemical symbols and formulae are the shorthand that lets chemists describe any substance precisely.
Part of your national curriculum
- Chemistry: the particulate nature of matter: Understand atoms, elements and compounds, and the use of chemical symbols and formulae
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
- • Atoms, elements and compounds
- • Reading a formula
- • The periodic table as a map
- • Mixtures are different
This lesson at a glance
- 28 minutes
- 21 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 21
Visual introductionPicture this
Atoms, elements and compounds
All matter is built from around a hundred kinds of atom. Chemical symbols and formulae are the shorthand that lets chemists describe any substance precisely.
In a nutshell
Understand atoms, elements and compounds, and the use of chemical symbols and formulae
Learning cycle
Part 2 of 21
Learning cycle 1 of 2
Part 1 · Atoms, elements and compounds
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 21
Learn
Atoms, elements and compounds
An element contains only one type of atom and cannot be broken down chemically. A compound contains two or more elements chemically bonded in fixed proportions, with properties usually very different from its elements. Sodium is a reactive metal and chlorine a toxic gas, yet sodium chloride is edible salt.
Reset break
Part 4 of 21
Pause
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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 5 of 21
Learn
Reading a formula
In H₂SO₄ the subscript applies to the symbol before it, so there are 2 hydrogen, 1 sulfur and 4 oxygen atoms: 7 atoms in total. Brackets multiply everything inside, so Ca(NO₃)₂ contains one calcium, two nitrogen and six oxygen atoms.
Quick check
Part 6 of 21
Quick check
Part 7 of 21
Reset break
Part 8 of 21
Pause
That's sitting 2 of 5 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 9 of 21
Learning cycle 2 of 2
Part 2 · The periodic table as a map
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 21
Learn
The periodic table as a map
Elements are arranged by atomic number, with metals to the left and non-metals to the right. Elements in the same group have similar chemical behaviour because they have the same number of outer electrons, which is why group 1 metals all react vigorously with water.
Explore the idea
Part 11 of 21
Learn
Mixtures are different
In a mixture the substances are not chemically bonded, keep their own properties and can be separated physically. Air is a mixture of gases; water is a compound. This distinction decides whether you need a physical separation technique or a chemical reaction.
Reset break
Part 12 of 21
Pause
That's sitting 3 of 5 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 13 of 21
Quick check
Part 14 of 21
Explore the idea
Part 15 of 21
Worked example
Worked answer: how many atoms are in one formula unit of Ca(NO₃)₂? (3 marks)
There is one calcium atom (1). The bracket contains one nitrogen and three oxygen atoms, and the subscript 2 outside multiplies everything inside, giving two nitrogen and six oxygen atoms (1). The total is 1 + 2 + 6 = 9 atoms (1). Ignoring the bracket gives 5, the most common error.
Reset break
Part 16 of 21
Pause
That's sitting 4 of 5 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 17 of 21
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
Challenge round
Part 18 of 21
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
A compound contains two or more ____ chemically bonded in fixed proportions, with properties usually very different from its elements.
Elements in the same group have similar ____ behaviour because they have the same number of outer electrons, which is why group 1 metals all react vigorously with water.
Challenge round
Part 19 of 21
Game · Recall cards
What is an element?
Card 1 of 4
Mastery quiz
Part 20 of 21
Marked quiz
End of lesson quiz: Atoms, elements and compounds
4 questions, marked with the reasoning shown. No timer.
1. What is an element?
2. What does the formula H2O tell you?
3. Why is water's formula different from a mixture of hydrogen and oxygen gas?
4. A compound is
Lesson round-up
Part 21 of 21
Lesson round-up
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Understand atoms, elements and compounds, and the use of chemical symbols and formulae