The statement that there is a periodic repetition of
chemical and physical properties of the elements when
they are arranged by increasing atomic number is called
the periodic law. The periodic table is organized in periods
(rows from left to right) and groups (columns from top
to bottom) by increasing atomic number. According to periodic
law, elements with similar chemical and physical properties
are in the same group. This is because they have the same
valence shell electron configuration.
Noble gasses, those in the group at the farthest right
of the periodic table (He, Ne, ..). These elements have
8 valence electrons and are extremely stable. The octet
rule suggests that to acquire the stable electron configuration,
atoms can gain, lose, or share electrons to achieve a
noble gas-like configuration.
Elements can be classified as metals, non-metals, or
metalloids. Trends exist in atomic radii, ionic radii,
ionization energy, and electronegativity. The ionization
energy measures how strongly an atom will "hold"
on to its electrons. Electronegativity, which can determine
the type of bond formation, is the ability of an element
to attract electrons in a chemical bond.