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ScienceAtoms, elements and mixtures30 min★★★ difficulty

Atoms, elements, compounds and formulae

Chemistry becomes much easier once you can tell an element from a compound from a mixture, and read what a formula is telling you. That is this lesson.

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

  • • One type of atom, or more
  • • Compound or mixture?
  • • Symbols and what numbers mean
  • • Brackets and big numbers

This lesson at a glance

  • 30 minutes
  • 19 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

elementscompoundschemicalsymbolsformulae

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%
1

Watch & discover

Part 1 of 19

Watch first

Atoms, elements, compounds and formulae

Clear up the difference between an element, a compound and a mixture.

Do it for real

The practicals below use what the film shows, with a full method you can follow at home.

Separating the colours in a felt-tip pen

In a nutshell

Understand atoms, elements and compounds, and the use of chemical symbols and formulae

2

What you already know

Part 2 of 19

Before we start

What you already know

You should know that all substances are made of tiny particles.

Recap: Variation within and between species
3

Key words

Part 3 of 19

Key words

Words you'll need today

Atom
The smallest particle of an element.
Element
A substance made of only one type of atom.
Compound
A substance in which different atoms are chemically bonded together.
Molecule
Two or more atoms bonded together.
Formula
Symbols and numbers showing which atoms, and how many, are in a substance.
4

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Elements and compounds

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 19

Learn

One type of atom, or more

An element contains one type of atom: copper, oxygen, carbon. There are about 118, arranged in the periodic table. A compound contains different atoms chemically bonded, like water or carbon dioxide, and its properties are usually nothing like those of the elements in it: sodium reacts violently with water and chlorine is toxic, yet sodium chloride is table salt.

6

Explore the idea

Part 6 of 19

Learn

Compound or mixture?

In a compound the atoms are bonded in fixed ratios and separating them needs a chemical reaction. In a mixture the substances are simply mixed in any proportion and can be separated physically. Air is a mixture; water is a compound. This distinction is tested constantly, so check for bonding before you answer.

7

Quick check

Part 7 of 19

Quick check

An element is a substance containing...

8

Quick check

Part 8 of 19

Quick check

How many atoms are in CaCO3?

9

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 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.

Stop here for now
10

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Reading and using formulae

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 19

Learn

Symbols and what numbers mean

Each element has a one- or two-letter symbol with only the first letter capital: Na, Cl, Mg, Fe. In H2O the small 2 applies to the hydrogen immediately before it, so there are two hydrogen atoms and one oxygen. In CaCO3 there is one calcium, one carbon and three oxygen atoms - five atoms in total.

12

Explore the idea

Part 12 of 19

Learn

Brackets and big numbers

A big number in front multiplies everything after it: 2H2O means four hydrogen atoms and two oxygen atoms. Brackets group atoms: Mg(OH)2 has one magnesium, two oxygen and two hydrogen atoms. Counting atoms accurately is exactly what you need for balancing equations in the next topic.

13

Quick check

Part 13 of 19

Quick check

Air is best described as a...

14

Quick check

Part 14 of 19

Quick check

Mg(OH)2 contains how many hydrogen atoms?

15

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

  • Only the first letter of a symbol is a capital: Co is cobalt, CO is carbon monoxide.
  • A compound is not a mixture - its atoms are chemically bonded in fixed ratios.
  • A small number applies only to the symbol immediately before it.
  • A compound's properties differ from those of its elements.
16

Challenge round

Part 16 of 19

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

17

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

In a compound the atoms are bonded in fixed ratios and separating them needs a ____ reaction.

18

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Atoms, elements, compounds and formulae

6 questions, marked with the reasoning shown. No timer.

  1. 1. A compound's atoms are...

  2. 2. How many atoms in 2H2O?

  3. 3. Which is written correctly?

  4. 4. Sodium chloride is safe to eat although sodium and chlorine are dangerous because...

  5. 5. Separating a compound requires...

  6. 6. A molecule is...

19

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 19 · Watch & discover

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    Understand atoms, elements and compounds, and the use of chemical symbols and formulae

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