1. As you go down a group the atomic size gets larger and the atoms have less attraction to the valence electrons, hence it becomes easier for them to be delocalized like in metals. As you move across the atoms get smaller and hold onto their electrons more.

2. Increasing as you go down is because you are adding energy levels to the electrons. As you go across you are staying within the same energy level and you are adding more protons, so the protons pull the electrons in a little closer so the atom gets smaller.

3. The ionization energy is the energy it takes to remove an electron, and the larger the atom is, the easier it is because the electrons will be further from the nucleus. So as you go down a group, atoms get bigger, the ionization energy drops. As you go across a period the atoms get smaller and the ionization energy increases.

4. The way I think about this one is that atoms don’t like to have extra or missing electrons, it’s unstable to have a large amount of extra charge in a small space.

So to add an extra electron it helps to have enough space so that it can spread out.

Think of trying to babysit 2 kids with 2 babysitters, if you add an extra kid it makes a big difference (especially if they’re all hyperactive). But if you had 10 kids and 10 babysitters, adding 1 kid wouldn’t be so bad.

So as you move across a period, atoms get smaller, and it’s more difficult to add electrons.

As you move down a group, atoms get larger and it’s easier to add electrons.

Extra note – if you know the size trends, all of the other ones can be rationalized using that.