Shielding & ionisation energy

Can someone pls explain what shielding is and why when it increases does first IE decrease? surely more shielding makes it harder for it to lose an electron gahhhh idkkkk

When we talk about shielding in atoms, it refers to shielding outer electrons from some of the positive charge of the nucleus. Extra shielding reduces the attraction between the nucleus and the outer electron being removed.

Imagine a magnesium atom. Its' outer electrons are in the 3rd shell, and there are 2 full shells of electrons closer to the nucleus. The negative charge in from the electrons in those inner shells "shields" some of the attractive effect of the positive charge from the protons in the nucleus on the outer shell electrons.

The effect of shielding is only partial - there will always be enough attraction between nucleus and outer electrons to maintain the atom's structure until some energy is applied.

so the more inner shells it has, the more shielding so the lower the IE as there are more electrons essentially blocking the positive charge from the nucleus???

If you are comparing elements in the same group, yes that is usually the case.

Worth noting that it isn't quite that straightforward. As well as increasing the shielding with more electrons there are more protons in the nucleus, so a greater positive charge. Additionally the more shells, the further the electrons are from the positive charge in the nucles - distance between charged particles reduces attraction.
These three (and possibly more) effects all have an influence on ionisation energy:
- shielding
- nuclear charge (number of protons)
- distance of outer electron from nucleus


Be careful about using words like "blocking" when it comes to answering questions in exams - it's more of a partial obscuration than blocking. Stick with 'shielding'