British Sign Language Glossaries of Curriculum Terms

BSL Chemistry Glossary - atomic number - Definition

Mass number and atomic number. Here we have a diagram of an atom; circling the outside there are electron/s; in the centre is the nucleus which is made up of neutrons and protons. Atoms come in different sizes and the one on the screen is a helium atom.

The chemical symbol for helium is He and if we look on the periodic table at the different elements they all have numbers attached to them which you can see here. 4 is the mass number and 2 is the atomic number.

How we work out these numbers is that the mass number is the number of protons added to the number of neutrons which in this case is 2 protons and 2 neutrons = 4. To work the atomic number we add up the number of protons which in helium is 2.

Summary: atomic number = number of protons and neutrons; mass number is the number of protons.