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 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
A proton is a positive particle that makes up the atom in the nucleus with a positive charge
The shell is the path that electrons follow outside the nucleus. Shells can be considered as energy levels and the further away from the nucleus the higher in energy.
The nucleus is the term given to the centre of the atom comprising of the proton and neutron
Nuclear charge is the attraction exerted by the nucleus on electrons due to the positive charge of the protons and negative charge of the electron
The inner shell are the electrons closest to the nucleus – usually the S and P shells due to their lower energy sub orbitals
Outer electrons is the term given to the shell/energy level furthest from the nucleus containing the electron furthest from the nucleus
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.