Relative Atomic Mass

Key Stage 3

Meaning

An element tile showing the mass number.

The Atomic Mass or mass number is the number of nucleons (protons + neutrons) in an atom.

About The Atomic Mass

Two atoms of the same element may have the same Atomic Number but a different Atomic Mass depending on the number of neutrons in the nucleus. Elements with different mass numbers are called isotopes.

The atomic mass is not affected by the number of electrons.

Only the particles in the nucleus affect the atomic mass.

Examples

Hydrogen	Helium	Lithium	Beryllium
Hydrogen has one nucleon so it has an atomic mass of 1.	Helium has four nucleons so it has an atomic mass of 4.	Lithium has seven nucleons so it has an atomic mass of 7.	Beryllium has nine nucleons so it has an atomic mass of 9.

Key Stage 4

Meaning

An element tile showing the mass number.

The relative atomic mass or mass number of an element is the number of nucleons (protons + neutrons) in an atom.

The relative atomic mass in grams is also the mass of one mole or 6.02x10²³ atoms of the element.

About Relative Atomic Mass

The relative atomic mass in grams on the Periodic Table tells the mass of a mole of the element. A mole of the element is 6.02x10²³ atoms of that element.

Two atoms of the same element may have the same Atomic Number but a different Relative Atomic Mass depending on the number of neutrons in the nucleus. Elements with different mass numbers are called isotopes.

The relative atomic mass is not affected by the number of electrons.

Only the particles in the nucleus affect the relative atomic mass.

Examples

Hydrogen	Deuterium	Tritium	Boron
Hydrogen has one nucleon so it has an atomic mass of 1 and 6.02x1023 (or 1 mole of) atoms of Hydrogen have a mass of 1g.	Deuterium has two nucleons so it has an atomic mass of 2 and 6.02x1023 (or 1 mole of) atoms of Deuterium have a mass of 2g.	Tritium has three nucleons so it has an atomic mass of 3 and 6.02x1023 (or 1 mole of) atoms of Tritium have a mass of 3g.	Boron has eleven nucleons so it has an atomic mass of 11 and 6.02x1023 (or 1 mole of) atoms of Boron have a mass of 11g.

References

Edexcel

Ar (relative atomic mass), page 167, GCSE Combined Science, Pearson Edexcel

Ar (relative atomic mass), page 23, GCSE Chemistry, Pearson, Edexcel

References

AQA

Relative atomic mass (Ar), pages 4-5, 64, GCSE Chemistry, Hodder, AQA

Relative atomic mass, A, pages 13, 21, 41, GCSE Chemistry; The Revision Guide, CGP, AQA

Relative atomic mass, A, pages 97, 123, GCSE Combined Science; The Revision Guide, CGP, AQA

Relative atomic mass, pages 100-1, GCSE Chemistry; Student Book, Collins, AQA

Relative atomic mass, pages 120, 177, GCSE Combined Science Trilogy 1, Hodder, AQA

Relative atomic mass, pages 26, 106, GCSE Combined Science Trilogy; Chemistry, CGP, AQA

Relative atomic mass, pages 26, 112, GCSE Chemistry, CGP, AQA

Relative atomic mass, pages 62-63, GCSE Chemistry; Third Edition, Oxford University Press, AQA