NucleusCopy

Learning Objectives

• Describe the composition of the nucleus in terms of protons and neutrons
• State the charges of protons and neutrons
• Use the term proton number Z
• Use the term nucleon number A
• Use the term nuclide and its notation
• Use and explain the term isotope
• State the meaning of nuclear fission and nuclear fusion
• Balance equations involving nuclide notation

Contents to learn

The nucleus
An atom consists of a central massive part called the nucleus and electrons revolving round the nucleus.

Most of the space in the atom is empty.

Almost the entire mass of the atom is concentrated in the nucleus which contains protons and neutrons.

We now believe that the nucleus of an atom is built up of protons and neutrons.

The particles that reside inside the nucleus are called nucleons.

An atom as a whole is neutral, as the number of protons in its nucleus is equal to the number of electrons revolving round it.

The proton number
Atomic number or charge number of an element is defined as the numbers of electrons revolving round the nucleus in a neutral atom, which is the same as the number of protons present in the nucleus of neutral atom.

Thus,

Z = Number of protons in the nucleus

OR

Z = Number of electrons in a neutral atom3

The nucleon number
The mass of an atom is specified by its mass number which is the total number of protons and neutrons present in the nucleus of the atom.

It is denoted by A.

Therefore,

A = Number of protons + Number of neutrons