Atomic Radius and Ionisation Energy Trends
Atomic radius gets smaller as you move across a period because there's greater attraction between the outer electrons and the nucleus. Think of it like a magnet getting stronger - the electrons get pulled in closer.
Ionisation energy is the energy needed to remove one outer electron from a gaseous atom. As you go across a period, this generally increases because electrons are closer to the nucleus and harder to remove. It's like trying to pull something away from a stronger magnet.
There are some clever exceptions to remember. Group 3 elements have lower ionisation energy than Group 2 because their outer electron sits in a p-orbital, which is easier to lose. Group 6 elements have lower ionisation energy than Group 5 due to electron-electron repulsions making it easier to remove an electron.
Quick Tip: The biggest jump between successive ionisation energies tells you which group an element belongs to - this often comes up in exam questions!
Going down a group, ionisation energy decreases because there's more shielding from inner electrons, reducing the attraction between nucleus and outer electrons.
