Bonds & Electronegativity

A molecule is made when two or more atoms form a chemical bond, linking them together. The two types of bonds are ionic bonds and covalent bonds. In an ionic bond, the atoms are bound together by the attraction between oppositely-charged ions.

The covalent bond is formed when two atoms are able to share electrons:

                                A*          +             B*           à           A * * B

whereas the ionic bond is formed when the "sharing" is so unequal that an electron from atom A is completely lost to atom B, resulting in a pair of ions:

                                A*          +             B*           à           A+   **B-

The two extremes of electron sharing represented by the covalent and ionic models appear to be generally consistent with the observed properties of molecular and ionic solids and liquids. A polar covalent bond is a covalent bond with a significant ionic character. This means that the electrons are closer to one of the atoms than the other, creating an imbalance of charge. A coordinate covalent bond is one where both bonding electrons are from one of the atoms involved in the bond. Lewis acids and bases. The electrons are shared roughly equally between the atoms in contrast to ionic bonding.

Electronegativity is a chemica property that describes the tendency of an atom to attract electrons toward itself and then the tendency to form negative ions. An atom’s electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus. The higher the associated electronegativity number, the more an element or compound attracts electrons towards it.

List the electronegativity values for H, Na, Cl, and O.

• H = 2.20
• Na = 0.93
• Cl = 3.16
• O = 3.44