Chapter 4

The Periodic Table

The periodic table arranges the elements in increasing atomic numbers. Its spatial layout is such
that a lot of information about an element’s properties can be deduced simply by examining its
position. The vertical columns are called groups, while the horizontal rows are called periods. There
are seven periods, representing the principal quantum numbers n = 1 to n = 7, and each period is
filled more or less sequentially. The period an element is in tells us the highest shell that is occupied,
or the highest principal quantum number. Elements in the same group (same column) have the
same electronic configuration in their valence, or outermost shell. For example, both magnesium
(Mg) and calcium (Ca) are in the second column; they both have 2 electrons in the outermost s
subshell, the only difference being that the principal quantum number is different for Ca (n = 4) than
for Mg (n = 3). Because it is these outermost electrons, or valence electrons, that are involved in
chemical bonding, they determine the chemical reactivity and properties of the element. In short,
elements in the same group will tend to have similar chemical reactivities.

Valence Electrons   and the Periodic    Table

Periodic    Trends  of  the Elements

Types   of  Elements

The Chemistry   of  Groups