State and explain the general trend in first ionization energy as you move across the period from left to right.

As you move across the period you are adding one more proton which increases the nuclear charge, you are also adding one more electron, however, the shielding provided by the extra electron is less than the extra nuclear charge so as you go across the period you get a net increase in the effective nuclear charge. As the effective nuclear charge increases the outer electrons are pulled in closer to the nucleus, this means that the ionization energy increases, as more energy is needed to remove the electron as it is held more strongly by the nucleus as it is closer to the nucleus.