An atom of an element with the same number of protons, but different mass numbers due to different numbers of neutrons.

A subatomic particle found in the nucleus with a relative mass of 1 and a positive charge (+1).

A subatomic particle found in the nucleus with a relative mass of 1 and no charge.

Is the total number of protons and neutrons in the nucleus of an atom.

The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.

Isotopes and relative atomic mass

Combined science

In the Structure and Bonding unit, pupils will build on their understanding of atomic structure to explore different types of chemical bonding and how these bonds affect the properties of substances.

In the Atoms, Elements and Compounds unit, pupils learned about the differences between atoms, elements, and compounds, as well as their chemical symbols and formulae.

Atomic structure and the periodic table

Subatomic particles with a mass of 1 and a positive charge.

Total number of protons and neutrons in an atom.

Atoms of an element with different numbers of neutrons.

Subatomic particles with a mass of 1 and no charge.

They are determined from the isotopes of the elements. 

Why do chlorine and copper have relative atomic masses which are not whole numbers, i.e. 35.5Cl and 63.5Cu?

Yes, as they have the same number of protons and a different number of neutrons.

No, as they have a different number of neutrons.

Yes, as they have the same number of electrons.

Yes, as they have a different number of neutrons.

No, as they have the same number of protons and electrons.

Will the isotopes of hydrogen H-1, H-2 and H-3 have the same chemical properties? Select the correct answer to explain why or why not.

Many isotopes are radioactive and can be used for medical purposes, however their abundance is very low. Calculate the abundance of Cr-50 when Cr-52 is 84.0%, Cr-53 is 9.5% and Cr-54 is 2.5%.

Calculate the relative atomic mass of silicon. The three silicon isotopes have atomic masses and relative abundances of 28 (92.2%), 29 amu (4.7%) and 30 amu (3.1%). Give your answer to 1d.p.

Bromine has a relative atomic mass of 79.9 (1d.p.). Bromine has two naturally occurring isotopes. Bromine-79 is 55% abundant. What is the mass number of the other isotope?

Which two subatomic particles are present in the nucleus of an atom?

number of protons = atomic number or proton number, for sodium = 11

number of electrons = same as the number of protons, for sodium = 11

mass number = total number of protons + neutrons

number of neutrons = mass number - number of protons, for sodium: 23 - 11 = 12

Order the method for working out the number of the three subatomic particles in an atom of sodium. Start with the number of protons, then work out the number of electrons, then finally neutrons.

Match the atoms with the number of neutrons in their nucleus. Use your periodic table to help.

³⁵Cl has 18 protons and ³⁷Cl has 20 protons.

³⁷Cl has gained two electrons to get a full outer shell.

³⁵Cl has 18 neutrons and ³⁷Cl has 20 protons.

³⁵Cl has 18 neutrons and ³⁷Cl has 20 neutrons.

Chlorine atoms mainly exist as ³⁵Cl and ³⁷Cl. Why are the mass numbers different?

This lesson will be removed by end of Summer Term 2025.

Isotopes and relative atomic mass

Lesson outcome

This lesson will be removed by end of Summer Term 2025.