Covalent Bonding

Recall that covalent bonding is sharing of electrons. It is usually a bond formed between two nonmetals You can use electronegativities to determine all if the bond is polar covalent or nonpolar covalent It is safe to say that nonpolar covalent bonds exist only when identical atoms are bonded to each other.

Bond Length and Bond Energy Remember that electrons of one atom are attracted to the nucleus of the other and visa versa. The atoms will approach each other until they reach a distance from each other that results in the possible potential energy.

Why do atoms from covalent Bonds? Octet Rule Since the outer shell of all noble gases (except Helium) hold eight electrons, the tendency of atoms to fill their outer energy level is the octet rule. First look at H 2 –Notice that both H fill their outer shell if they share them equally

Bond Length and Bond Energy At the minimum potential energy, the distance between the two atoms is known as the bond length The bond energy is the amount of energy needed to break the bond, and is a measure of the strength of bond The bond length and bond energy vary depending on the atom involved in the bond.

Bond Length

Not all bond lengths are the same H-H bond is the shortest (0.074nm) As you move down a group the bond length becomes longer Multiple bonds are shorter than single bonds C-C  nm C=C  nm

Covalent bonds allow atoms to have the same electron conf. as noble gases What so all the electron configurations of noble gases have in common? Draw the bonding of two Hydrogen Draw the bonding of two Fluorine Draw the bonding of H-Cl

Octet Rule All atoms want 8 electrons in the valance shell. (H – 2) Exceptions: –Boron, which only has three valance electrons, tends to form bonds in which it is surrounded by six electrons

Other Exceptions Other elements can be surrounded by more than 6 electrons by using their d orbital Since the d orbital are used for this, only elements whose atoms have a d orbital can do this. The first d orbital is found in the third energy level, so any atom with three or more energy levels can exceed the octet rule Keep in mind that the octet rule is the goal, and these exceptions are possible.

Molecules Many things around you, such as sugar, propane, and gasoline are composed of molecules Molecules are neutral groups of atoms that are help together by covalent bonds Compounds that consists of molecules are known as molecular compounds, or since they are held together by covalent bonds, they can be called covalent compounds

Molecules In lab we often use Methane gas Methane is composed of carbon and hydrogen, both of which are nonmetals, which means the bonds in methane are covalent. Since it is held together by covalent bonds, a sample of methane gas is a molecular compound, and is made up of methane molecules.

Methane The picture shows a molecule of methane Which contains a C atom and 4 H atoms This information can be summed up in the chemical formula, which uses the symbol of the elements and subscripts to indicate the number and type of each element in a compound CH 4

Review On a sheet of paper write as much as you can on the following topics, include as many terms as possible: Chemical bonding Covalent bonds Ionic bonds Octet rule Polar and Nonpolar Bond Length Molecules