Question

How strong is the attractive force of the nucleus on electrons?

Answer 1

The attractive force of the nucleus on its electrons is known as the effective nuclear charge (`Z_(eff)`), and decreases as you get further from the nucleus.

The nucleus is positive and the electrons are negative, which obviously means they attract. However, electrons are organised into shells, and so as you move further out, you have more shells of electrons in the way of the nucleus, which repel the outermost electrons a little more.

This is known as the shielding effect, and is why the nucleus only has a weak hold on electrons far away - they are being repulsed slightly by closer electrons.

You can roughly calculate the effective nuclear charge by the equation

`Z_(eff) = Z - S`,

where `Z` is the atomic number (no. of protons) and `S` is the number of shielding electrons. As you move further from the nucleus, `S` increases, and so `Z_(eff)` decreases.

The force, compared to other forces, is relatively strong, because the distance is so short. Electromagnetism is overall the second strongest force, after the Strong Nuclear Force (but that is ineffective except over very tiny distances).