Forming single, double, and triple bonds 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 pairs (shown by lines) Lone Pairs: Unshared pairs (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 1 Examples: F2, NH3, CH4 The sharing of ______ pair of electrons Examples: F2, NH3, CH4 C H F H N

Double Covalent Bonds 2 Examples: O2 and H2CCH2 The sharing of ______ pair of electrons Examples: O2 and H2CCH2 O C H

Triple Covalent Bonds 3 Examples: N2 and HCN The sharing of ______ pair of electrons Examples: N2 and HCN N N C H

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

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

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

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

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 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 H2O CF4

NCl2Br CO2

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

Let’s look at CO32- and NH4+1