SOME IMPORTANT PERIODIC TRENDS
For the SAT Chemistry Subject Test, you’ll need to know about four important
trends seen in the periodic table.
Ionization Energy Because the atomic nucleus contains protons, nuclei are
positively charged; the attraction between opposite charges is what keeps the
negatively charged electrons in their orbitals. In order for an electron to be
extracted from an atom (which creates a positively charged ion), energy must be
expended. For any atom, the amount of energy required to remove an electron
from an atom is called the ionization energy. As you move from left to right
across the periodic table, ionization energy generally increases; it gets much
harder to remove an electron from the atom. As you move from top to bottom
through a column (group), ionization energy decreases. Also, it is much harder to
remove each successive electron from an atom; the energy required to remove an
inner (nonvalence) electron from an atom is incredibly high because these
electrons are very strongly attracted to the atom’s nucleus. For the exam,
remember that ionization energy increases from left to right across the
periodic table as you move up through a group. Ionization energy increases as
you move towards fluorine.