How does atomic size differ with groups in the periodic table?

The periodic table may seem like a very confusing place to be. However in contrast it is very simple to understand when you know what you are looking for. The table does not in any way shape or form need to be memorised and in some ways, if used well can do the chemistry for you. Reading the periodic table is a necessity in learning chemistry and can be a powerful tool if taught properly.
So what can we take from this table? Well one good example that can be drawn from it, is with regards to atomic radius size. We know from simple school chemistry that heavier elements have more and more protons, electrons and neutrons added. Ok.. So how does this effect size? Size is altered by three main effects; nuclear charge; electron shielding and distance from the nucleus. 
So let’s look at Carbon, Nitrogen and Oxygen. Nitrogen has one extra proton and electron than Carbon and similarly Oxygen to Nitrogen. Each proton has +1 positive charge. So the more protons the element has the greater the nuclear charge. The addition of an extra electron in all three cases will go into the same subshell. This will result in the electron shielding not increasing but the nuclear charge will.
This causes a greater 'pull' on the electrons in the outer orbitals decreasing size. So basically as you go further to the right in each group the general trend is that element atomic radius will decrease in size.