Why does ionization energy increase as you move from left to right across the periodic table?

Why does ionization energy decrease as you move down a periodic group?

What two factors affect ionization energy?

Why is the gallium atom a little bit larger than the zinc atom?

Atomic size decreases from left to right across the periodic table because

Why does the atomic size of the elements increase as you look down the first group?

What effective nuclear charge do the outermost electrons experience on a fluorine atom?

Why doesn't the outer electron on the potassium atom experience the full charge of the protons in the nucleus (+19)?

What is a periodic trend?

What do the elements He, Ne, Ar (the noble gases) all have in common in relation to the electrons in their outermost shell?