Nuclear Charge


Nuclear charge is a measure of the effect of the number of protons in the nucleus and their ability to attract the negative electrons in orbits around the nucleus.

Electrons are attracted to the nucleus as they are negatively charged and the nucleus contains positively charged protons, but at the same time the layers of sub orbitals of electrons repel each other. This results in a varying attraction of the nucleus on the outer electron known as nuclear charge. The presence of electrons on the inner shells of an atom reduces the effect of this nuclear charge so often we refer to the effective nuclear charge which is the effect of the nucleus experienced by the outer electron of the atom.

We can calculate the effective nuclear charge by subtracting the number of inner shell electrons from the number of protons. For example Sodium has 10 inner electrons and 11 protons so 11-10 gives it an effective nuclear charge of +1. But looking at Magnesium which has 10 inner electrons as well but 12 protons it has an effective nuclear charge of +2.

The amount of charge influencing an outer electron can be determined by measuring the charge of the nucleus, the charge of the electron and proton and also the radius between the proton and electron. We can use coloumbs law to calculate the effective force of a nucleus on an electron. By multiplying the coloumbs law constant (k) by q1, the effective nuclear charge and q the charge of the electron and dividing by he radius squared we can work out F which is the force of attraction between the nucleus and the outer electron.

Terms in section

A proton is a positive particle that makes up the atom in the nucleus with a positive charge


A neutron is a neutral sub atomic particle that makes up the nucleus with the proton


The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus

Inner shell

The inner shell are the electrons closest to the nucleus – usually the S and P shells due to their lower energy sub orbitals

Outer shell

Outer electrons is the term given to the shell/energy level furthest from the nucleus containing the electron furthest from the nucleus

Effective nuclear charge

The effective nuclear charge is the attraction of the nucleus to the valence electron taking into account the number of protons and the number of inner shell electrons.

Coloumbs law

Coloumbs law relates the effective nuclear charge and the radius of the atom and charge to measure the attractive force of a nucleus

Sub orbitals

Sub orbitals are the orbitals with the S P D and F shells that have their own unique quantum numbers and spin patterns when electrons are treated as waves


Atomic Radius