Summary: Atomic Structure
Atoms consist of protons and neutrons in the nucleus, surrounded by
electrons that reside in orbitals. Since electrons are wave-like in
behavior, it is impossible to determine the exact position of an electron.
Instead, orbitals describe regions in space where electrons are likely to
reside. Orbitals are classified according to the four quantum numbers that
represent any one particular orbital's energy, shape, and orientation.
Electrons
fill up these orbitals in a systematic fashion, with two electrons per orbital.
When considering the electron configuration of atoms it is useful to
consider the valence electrons separately from the inner electrons, since
much of the chemistry that elements undergo occurs as a result of the octet
rule. The octet rule is the tendency for atoms to gain a full valence shell
of
electrons. For that reason, elements with similar valence shell configurations
have similar chemical properties, giving rise to much of the periodicity of the
Periodic Table.
Two such period properties are an atom's ionization energy and its
electron affinity, which are the energies involved when an atom loses and
gains electrons, respectively. An atom's ionization energy and electron
affinity determine how easily that atom can lose or gain electrons and thereby
form ions with a full valence shell. In gaining and losing electrons atoms
also can become positively or negatively charged. When positive and negative
ions interact, this gives rise to attractive forces that form the basis of
ionic bonding.
