GCSE Physics · key term

Mass (nucleon) number

Definition

The total number of protons and neutrons in an atomic nucleus; it is represented by $A$ .

Used by Edexcel

Specification 6.3, 6.20 · Paper 1

Together, these particles are called nucleons. The numbers of these particles describe the structure of a particular nucleus.
Revise: Isotope Structure
The total number of protons and neutrons in a nucleus, written as $A$ .
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
Mass number is a whole number for one particular isotope. Do not confuse it with the relative atomic mass shown as a decimal on many periodic tables.
3
State the change in both numbers: the atomic number, $Z$ , and the mass number, $A$ .

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GCSE Physics · key term

The total number of protons and neutrons in an atomic nucleus; it is represented by $A$ .

Used by Edexcel

Specification 6.3, 6.20 · Paper 1

Together, these particles are called nucleons. The numbers of these particles describe the structure of a particular nucleus.
Revise: Isotope Structure
The total number of protons and neutrons in a nucleus, written as $A$ .
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
Mass number is a whole number for one particular isotope. Do not confuse it with the relative atomic mass shown as a decimal on many periodic tables.
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.