Covalent Bonds Forming single, double, and triple bonds

Covalent Bonding Remember, when atoms bond covalently, there is a sharing of electrons between the two atoms. However, not all of the electrons are involved in the bond, so there are two different types of electron pairs. Bonding Pair: Shared (shown by lines) Bonding Pair: Shared (shown by lines) Lone Pairs: Unshared (shown by pairs of dots) Lone Pairs: Unshared (shown by pairs of dots)

There are also a few types of covalent bonds and the type of covalent bond depends on how many pairs of electrons are shared.

Single Covalent Bonds The sharing of ______ pair of electrons 1 Double Covalent Bonds Triple Covalent Bonds The sharing of ______ pair of electrons 2 3

Strength of Bonds Distance separating nuclei - _________ ___________ Depends on the size of the atoms - _________ ___________ Depends on the size of the atoms - _________ ___________ Pairs shared – more electrons shared, _________ ___________ Pairs shared – more electrons shared, _________ ___________ (_____________ has smallest bond length) Smaller bond length - _________ ___________ Smaller bond length - _________ ___________ bond length radii closertogether atomic Triple bond bond stronger

Strength of Bonds Bond dissociation energy – energy to _________ ___________ Energy must be _________ to break bonds Direct relationship between bond energy and bond length - _________ bond length, _________ bond, _________ bond energy bondsbreak added smaller stronger more

So, how do scientists decide how many electrons are shared? One way is by drawing Structural Formulas a.k.a. Lewis Formulas

Rules: 1.Add up total number of ________ electrons. 2.Place atoms on center or sides....how? 3.Connect each atom with a _________ bond, then subtract from total number (2 per line). 4.If any electrons are left, place pairs of electrons on the __________ atom(s) until they are “___________”. Remember, Hydrogen can only make ______________ valence single one single bond Single element in center first Least electronegative in center if there is a choice Hydrogen is never in the middle happy outside

5. If any electrons are left, place them on the center atom. 6. When you are at 0 pairs, make sure everyone is “happy”: Happy Hydrogen :____________Happy Hydrogen :____________ Happy everyone else:__________Happy everyone else:__________ 7. Remember a line represents ___ electrons. 8. If everyone is happy then.....Finished. If everyone is not happy then you must share extra pairs and form double or even triple bonds. 2 electrons 8 electrons 2

Let’s try some examples H 2 O CF 4

NCl 2 Br CO 2

Polyatomic Ions 1.Take charge into consideration. (Add negative to total, subtract positive from total of electrons.) 2.Put brackets around structure with charge on outside right corner

Let’s look at CO 3 2- and NH 4 +1