GCSE Physics · key term

Atomic (proton) number

Definition

The number of protons in an atomic nucleus; it identifies the element and is represented by $Z$ .

Used by Edexcel

Specification 6.3, 6.20 · Paper 1

An atomic nucleus contains protons and neutrons. Together, these particles are called nucleons. The numbers of these particles describe the structure of a particular nucleus.
Revise: Isotope Structure
The number of protons in a nucleus, written as $Z$ . It identifies the element.
Revise: Effects of Decay

1
In ${}^{A}_{Z}X$ , read the upper number as the mass number and the lower number as the atomic number; do not reverse them.
2
When deciding whether two atoms are isotopes, compare their atomic numbers first: isotopes must have the same $Z$ but different $A$ .
3
State the change in both numbers: the atomic number, $Z$ , and the mass number, $A$ .

Create a free account to read GCSE Physics revision notes for your exam board and track your progress.

GCSE Physics · key term

The number of protons in an atomic nucleus; it identifies the element and is represented by $Z$ .

Used by Edexcel

Specification 6.3, 6.20 · Paper 1

An atomic nucleus contains protons and neutrons. Together, these particles are called nucleons. The numbers of these particles describe the structure of a particular nucleus.
Revise: Isotope Structure
The number of protons in a nucleus, written as $Z$ . It identifies the element.
Revise: Effects of Decay

1
In ${}^{A}_{Z}X$ , read the upper number as the mass number and the lower number as the atomic number; do not reverse them.
2
When deciding whether two atoms are isotopes, compare their atomic numbers first: isotopes must have the same $Z$ but different $A$ .
3
State the change in both numbers: the atomic number, $Z$ , and the mass number, $A$ .

Create a free account to read GCSE Physics revision notes for your exam board and track your progress.