what is energy trend
Veiw a periodic table with first ionization energies. Definition: Second Ionization Energy is the energy required to remove a second outermost electron from a ground state atom. Subsequent ionization energies increase greatly once an ion has reached the state like that of a noble gas.) As you move across a period, first ionization energy increases. WHY? - As you move across a period, the atomic radius decreases, that is, the atom is smaller. The outer electrons are closer to the nucleus and more strongly attracted to the center. Therefore, it becomes more difficult to remove the outermost electron.