Covalent Bonding

Sharing Electrons
Example~ A hydrogen atom has one electron. If it had two electrons, it would have the same electron configuration as a helium atom. Two hydrogen atoms can achieve a stable electron configuration by sharing their electrons and forming a Covalent bond. A covalent bond is a chemical bond in which two atoms share a pair of valence electrons. When two atoms shair one pair of electrons, the bond is called a singe bond.

Molecules of Elements
Two hydrogen atoms bonded together form a unit called a molecule.
A molecule is a neutral group of atoms that are joined together by one or more covalent bonds.
The hydrogen molecule is neutral because it contains two protons. (one for each atom) and two electrons (one for each atom).
What keeps the hydrogen atoms together in the molecule?
The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond.
A chemical formula can be used to describe the molecules of a element as well as a compound.

Multiple covalent bonds
Nitrogen has five valence electrons. If two nitrogen atoms shared a pair of electrons, each one would have only six valence electrons.
If they shared two pairs of electrons, each atom would only have seven valence electrons.
When the atoms in nitrogen molecule share three pairs of electrons each atom has eight valence electrons.
Each pair of shared electrons is represented by a long dash in the structural formula N=N.
When two atoms share three pairs of electrons, the bond is called triple bond.
When two atoms share two pairs of electrons, the bond is called double bond.

Unequal Sharing of Electrons
In general, elements on the right of the periodic table have a greater attraction for electrons than elements on the left have (except for the noble gasses)
In general, elements at the top of a group have a greater attraction for the electrons than elements at the bottom of the group have.

Polar Covalent Bonds
In a molecule of an element, the atoms that form bonds have the same ability to attract a electron.
Shared electrons are attracted are attracted equally to the nuclei of both atoms.
In a molecule of a compound, electrons may not be shared equally.
A covalent bond in which electrons are not shared equally is called a polar covalent bond.
When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge.

Polar and nonpolar Molecules
The type of atoms in a molecule and its shape are factors that determine weather a molecule is polar or nonpolar.

Attraction between Molecules
In a molecular compound, there are forces of attraction between molecules. These attractions are not as strong as ionic or covalent bonds, but they are strong enough to hold molecules together in a liquid or solid
Attractions between polar molecules are stronger than attractions between nonpolar molecules.