Covalent Compounds

Covalent Compound Electrons are shared between 2 different atoms – 1 bond forms between two elements that each share one electron with the other element Usually formed between two nonmetals Covalent compounds = molecules

3 types of bonds Single bond – 1 set of electrons shared Double bond – 2 sets of electrons shared Triple bond – 3 sets of electrons shared In terms of strength: Triple > double > single

Drawing Lewis Dot diagrams for Covalent compounds Example: CF 4 1.Determine the total number of valence electrons in the compound C = 4 v.e. F = 7 v.e. x 4 atoms of F = 28 v.e. 4+28= 32 v.e. in the molecule

2. Write the elements for the molecule so that the least electronegative element is in the center. (Usually the molecule that can make the most bonds will be in the center)

3. Add covalent bonds between the central and outside atoms. (Remember: every bond = 2 electrons) 4 bonds x 2 electrons = 8 electrons 32-8 = 24 electrons left

4.Add lone pairs of electrons to the outside atoms until each contains a total of 8 electrons (unless it is H) - Octet rule 4 F each with 3 lone pairs (each lone pair has two electrons) So…4 x =32 electrons, this is the lewis structure for CF 4

5. Add lone pairs to the central atom if there are any left over. Example: Draw the Lewis structure for NH 3

6. Make sure every element has 8 v.e. (except H = 2 and B= 6), add double and triple bonds if necessary to complete the octet rule for each element. Example: Draw the Lewis structure for CH 2 O

Properties of Covalent Compounds Lower melting point than ionic compounds Most are liquids or gases – If solid, not as hard as ionic compounds Weak interparticle forces between molecules Do not conduct electricity or heat