Sharing of Electron Pairs Non-metal with Non-metal Atoms 2.1 Covalent Bonding Sharing of Electron Pairs Non-metal with Non-metal Atoms

Learning Goals By the end of this lesson you will be able to: Be able to define covalent bond Be able to react 2 non-metals to create covalent bond Use the octet rule to for stable covalent molecules.

Covalent Bonds Bond formed by a shared pair of electrons between 2 non-metal atoms Gives atom an octet of electrons Shared pair of electrons – bonding pair Other electrons not involved in bonding – nonbonding pairs (a.k.a. lone pairs) Covalent bonds can be either 1) non-polar covalent 2) polar covalent (to be discussed later)

Covalent Bonds example Chlorine does not occur in nature as an isolated atom Cl Cl Cl Bonding Pair Cl Cl Lone Pair Chlorine atoms share electrons to get full shell

Cl Cl Review of Octet rule 8 7 8 7 1 6 1 6 2 5 5 2 3 4 3 4 Octet rule - most covalently bonded atoms represented in a Lewis structure have 8 electrons in their valence shells. 8 7 8 7 Cl Cl 1 6 1 6 2 5 5 2 3 4 3 4

H H H2 F2 F I2 Br2 I Cl2 Br Cl Diatomic Molecules Fluorine Bromine Hydrogen Halogens H H H2 F F2 Br Br2 Fluorine Bromine Cl I I2 Cl2 Chlorine Iodine

Dash Notation for Covalent bonds Since the dots for electrons get crowded, dashes can be used to represent a covalent bond H H H2 H H

Multiple Bonds Atoms may share more than one pair of electrons a DOUBLE BOND forms when atoms share two pairs of electrons (4 e-) a TRIPLE BOND forms when atoms share three pairs of electrons (6 e-) Total number of bonds per atom unchanged

Multiple Covalent bonds Only 7 electrons does Not meet Octet Rule! Need to share Another pair of electrons O O Sharing One Pair of electrons One Covalent Bond O O O O A Double Bond can be represented by a double line Sharing Two Pairs of electrons Two Covalent Bonds A Double Bond

Multiple Covalent bonds Nitrogen N N Sharing Three Pairs of electrons Three Covalent Bonds A Triple Bond N N A Triple Bond can be represented by a Triple line

Multiple Bonds C2H4 Valence e- = 12 H2CO Valence e- = 12 4 Bonds, each carbon H2CO Valence e- = 12 Two bonds at oxygen

Multiple Bonds Total valence e- = 16 (Oxygen = 6 e-, each; Carbon = 4 e-. Four bonds/C; 2 bonds oxygen Total valence e- = 10 (H=1, C=4, N=5) Bonds: C=4, N=3, H=1 Total valence e- = 18 (O=6, Cl = 7, P = 5) Bonds: Cl=1, P=3, O=2

Naming Covalent Compounds Common Names Water H2O Ammonia NH3 Methane CH4 O H N H C H

Patterns for Major Elements CH4 C = 4 bonds; all electrons shared NH3 N = 3 bonds; one lone pair H2O O = 2 bonds; two lone pairs HF F = 1 bond; three lone pairs

4 Bonds All e- shared Carbon, group IV 3 Bonds 1 Lone Pair Nitrogen, Group V 2 Bonds 2 Lone Pairs Oxygen, Group VI 1 Bond 3 Lone pairs Fluorine, Group VII

Other Compounds Have Same Pattern C = 4 bonds; Cl (like F) = 1 bond P (like N = 3 bonds; Br (like F) = 1 bond

More Similarities: S (like Oxygen) = 2 bonds, 2 lone pairs C = 4 bonds; O = 2 bonds, 2 lone pairs

Predicting Dot Diagrams How Do We Proceed? Determine total number of valence electrons Based on usual bond nos., identify reasonable layout for atoms Place bonding electrons between atoms to make usual no. of bonds Place remaining electrons as lone pairs around atoms still lacking an octet

Total number of Valence e- Sum of group numbers for atoms of representative elements Eg., C = 4e- N = 5e- O = 6e- H = 1e- CCl4 = 4e- + (4 x 7e-) = 32e- SO2 = 6e- + (2 x 6e-) = 18e- N2H4 = (2 x 5e-) + (4 x 1e-) = 14e- C3H8 = (3 x 4e-) + (8 x 1e-) = 20e-

Based on Covalence (Usual Bonds) Nos. Reasonable Layouts Based on Covalence (Usual Bonds) Nos. H2S -- 1 Bond each H; 2 Bonds for S H-H=S Incorrect - One H has 3 bonds H-S-H Correct - All atoms with usual bond numbers (H=1; S=2) PCl3 Cl=P-Cl-Cl Incorrect - One Cl has two bonds Cl-P-Cl Correct -- (Cl=1; P=3) | Cl

Practice OF2

Layout: O-F-F

Layout: O-F-F Incorrect -- One F with two bonds; O only one bond

Layout: O=F-F

Layout: O=F-F Incorrect -- One F with three bonds; (O does have two bonds)

Layout: F-O-F

Layout: F-O-F Correct -- F = 1 bond, each; O = 2 bonds)

Practice Place bonding electrons for connected atoms

Practice Place bonding electrons for connected atoms

Practice Add lone pairs for atoms needing “octet”

Practice Add lone pairs for atoms needing “octet”

Practice Similarly, add lone pairs for fluorines:

Practice Check Results! Correct total e- (O = 6; F = 7, ea) = 20e- Usual bond nos. (O=2; F=1, ea) Closed shell (octets) O=8; F=8 each

Now You Do One: Now You Do One: CH2CL2

Total e- C = 4 e- H = 1e-, each, 2 total Cl = 7e-, each = 14 more Grand total = 20e-

Layout: H-H-C-Cl-Cl

Layout: H-H-C-Cl-Cl Incorrect

Layout: H-C-Cl-Cl-H Incorrect

Layout: H-H-Cl=C=Cl Incorrect

Layout: C H Cl Correct!

Check Results: Total e- Usual no. Bonds Closed Shells

And Another OCS

C = 4e- O = 6e- S = 6e- Total = 16e- Number e- C = 4e- O = 6e- S = 6e- Total = 16e-

Layout? O C S or C S O S O C ??

2 Bonds for O; 4 Bonds for C; 2 Bonds for S Layout O=C=S 2 Bonds for O; 4 Bonds for C; 2 Bonds for S

Great!