Chemical Bonding

Chemical reactions involve the making and breaking of bonds. It is essential that we know what bonds are before we can understand any chemical reaction. To understand bonds, we will first describe several of their properties. The bond strength tells us how hard it is to break a bond. Bond lengths give us valuable structural information about the positions of the atomic nuclei. Bond dipoles inform us about the electron distribution around the two bonded atoms. From bond dipoles we may derive electronegativity data useful for predicting the bond dipoles of bonds that may have never been made before.

From these properties of bonds we will see that there are two fundamental types of bonds--covalent and ionic. Covalent bonding represents a situation of about equal sharing of the electrons between nuclei in the bond. Covalent bonds are formed between atoms of approximately equal electronegativity. Because each atom has near equal pull for the electrons in the bond, the electrons are not completely transferred from one atom to another. When the difference in electronegativity between the two atoms in a bond is large, the more electronegative atom can strip an electron off of the less electronegative one to form a negatively charged anion and a positively charged cation. The two ions are held together in an ionic bond because the oppositely charged ions attract each other as described by Coulomb's Law.

Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape