Chemistry

Chapter 9

9.1/9.2 Notes Part 2

Review

• Covalent Bonds– Sharing of valence electrons– Still atoms are trying to meet the octet rule– # of unpaired valence electrons decides how

many bonds an atom can make– Use electron dot structures to see how many

unpaired electrons there are in an atom– Bonds can be single, double, or triple

Single Bonds• One shared pair of

electrons• Total of 2 e- in the

bond• Also called a “sigma”

bond– It just refers to the fact

that there is a direct overlap between the outer energy levels of the atoms that are sharing e-

Multiple Bonds

• Double Bond – 2 shared pair– 4 e- total– 1 sigma– 1 pi

• Triple Bond– 3 shared, 6 e-– 1 sigma– 2 Pi (parallel overlap)

Double bond –

Red in the center = sigma

Green = Pi (above & below)

Strength of Bonds

• Bond Length– The closer the nuclei are, the stronger the

bond– More shared pair = closer the nuclei are

• Bond Dissociation Energy– Amount of energy it takes to break a covalent

bond– As bond length decreases, the bond

dissociation energy increases

Covalent Compounds

• Properties– Nonconductors– Low melting – Low boiling point– Mostly gas at room temp– Solids are soft and brittle

Covalent Network Solids

• Graphite V. Diamond – (allotropes)

• Covalent Network Solids– Examples: diamond and Quartz– Covalently bonded in a crystal lattice (like an ionic

compound) - a continuously bonded structure– Hard, rigid– High melting and boiling points– nonconductors

Lewis Structures

• Electron diagrams of multiple atoms to show how they are arranged in molecules

• Ex. H2 H2O Ammonia

• Methane O2 CO2