BONDING
Atoms are rarely found in their elemental form but are usually found bonded to other
atoms as part of compounds. A bond is composed of a group
... [Show More] of negatively charged
valence electrons between the atoms that simultaneously attract the positively charged
nuclei of both atoms. Since the two atom nuclei are attracted to the same group of
electrons, they remain together. Atoms bond because are more stable together. They are
more stable together because energy is released in the bond-forming exothermic
reaction. Bonds are of two types that differ in the way the valence electrons involved are
arranged.
Ionic Bonding
One type of bond is called an ionic bond because the bond is formed between
oppositely charged ions. This type of bond is said to be formed by electron
transfer (simultaneous loss and gain of electrons to form ions). Ions are charged
particles formed by an atom either losing one or more electrons to form a positively
charged ion (called a cation because it is attracted to the negatively charged pole
(cathode) of an electric field) or by an atom gaining one or more electrons to form a
negatively charged ion (called an anion because it is attracted to the positively charged
pole (anode) of an electric field). These ions are usually formed by atoms transferring
electrons during chemical reactions to form oppositely charged ions that attract one
another (an ionic bond). Several examples of ions and their formation are shown below:
2 Na + Cl2 → 2 Na+ + 2 Cl2 Ca + O2 → 2 Ca+2 + 2 O-2
2 K + S → 2 K+ + S-2
Al + N → Al+3 + N-3
The charge on an ion is determined by how many electrons are lost or gained and
whether the atom loses electrons (metal atoms, because of their lower
electronegativity, tend to lose electrons forming positive ions) or gains electrons
(nonmetal atoms, because of their higher electronegativity, tend to gain
electrons forming negative ions). The number of electrons lost or gained is
determined by the octet rule, which states that atoms tend to gain or lose (or share)
electrons so as to achieve eight electrons in their outer shell. This is the same electron
arrangement as that of the most stable atoms in the periodic table, the group VIII, inert
gas atoms. Metals will tend to lose all of their outer shell electrons to uncover
an inner shell that has eight electrons, and nonmetals will tend to gain enough
electrons to complete an outer shell of eight. That is why, in the above examples:
Sodium loses its one outer shell electron to form a Na+
ion.
Calcium loses its two outer shell electrons to form a Ca+2 ion.
Aluminum loses its three outer shell electrons to form an Al+3 ion.
Chlorine gains one electron into its outer shell of seven to form a Clion.
Oxygen gains two electrons into its outer shell of six to form an O-2 ion.
Nitrogen gains three electrons into its outer shell of five electrons to form a N-3 ion.
Formation of Inert Gas (Octet) Electron Struct [Show Less]