STUDENT SPACE · TOPIC 1

Atoms and elements

Distinguish an element from a compound and describe the structure of an atom.

The essentials

An element contains one type of atom. A compound contains different elements chemically combined in a fixed ratio.
Protons and neutrons are in the nucleus; electrons occupy shells around it.
A neutral atom has equal numbers of protons and electrons.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

A molecule contains two nitrogen atoms. Is it an element or a compound?

Need a hint for Question 1?

Count the types of atoms, not just the number of atoms.

Check Question 1

It is an element because it contains only nitrogen atoms. Two atoms do not necessarily mean two different elements.

Classify O₂, H₂O and air as element, compound or mixture. Give a reason for each.

Need a hint for Question 2?

Count the types of atoms and ask whether they are chemically combined.

Check Question 2

O₂: element, one type of atom. H₂O: compound, different elements chemically combined. Air: mixture, substances mixed without chemical combination.

A neutral atom has 8 protons and 8 neutrons. State its number of electrons and explain its overall charge.

Need a hint for Question 3?

A neutral atom has balanced positive and negative charges.

Check Question 3

8 electrons. The total positive charge from 8 protons cancels the negative charge from 8 electrons.

Use the matching chapter worksheet. Attempt independently, compare your reasoning with your partner, then bring unresolved questions to your teacher.

Change the number of neutrons and compare isotope mixtures.