1. Chemical Bonding Chemical bonds are classified into two types:
Ionic bonding results from electrostatic attractions among ions, which are formed by the transfer of one or more electrons from one atom to another.
Covalent bonding results from sharing one or more electron pairs between two atoms.

2. Chemical bonds are the attractive forces that hold atoms together in compounds.
The electrons involved in bonding are usually those in the outermost (valence) shell.

3. (aqueous) Physical Properties of Ionic and Covalent Compounds
Ionic Covalent
Melting Pt High Low
Solubility Soluble Insoluble
(polar solvents)
Solubility Insoluble Soluble
(nonpolar solvents)
Conductivity High Low
(molten)
Conductivity High Low
(aqueous)

4. The Lewis dot representation
(Lewis dot formulas, Lewis dot structures)
convenient bookkeeping method for valence electrons
electrons that are transferred or involved in chemical bonding
Table 7-1
pg. 272

5. metals react with nonmetals to form ionic compounds
2Li(s) + F2(g)  2LiF(s)
1s s p
Li 
F   becomes
Li+  [He]
F-  [Ne]
Table 7-2
pg. 277

6. Groups Gen. Form. Example
IA + VIIA MX NaF
IIA + VIIA MX BaCl2
IIIA + VIIA MX AlF3
IA + VIA M2X Na2O
IIA + VIA MX BaO
IIIA + VIA M2X Al2S3
IA + VA M3X Na3N
IIA + VA M3X Mg3P2
IIIA + VA MX AlN
H forms ionic cpds. with IA + IIA metals
LiH, KH, CaH2, BaH2,, etc.
other H cpds are covalent

7. Covalent Bonding .. Covalent bonding results from sharing one or more
electron pairs between two atoms.
Covalent Bonding occurs when two atoms with similar
electronegativities form a bond
share 2 electrons - single covalent bond
share 4 electrons - double covalent bond
share 6 electrons - triple covalent bond
H-H
O=O
NN .. .. .. = .. .. .. ..

9. Octet Rule and Lewis Formulas for Molecules
octet rule - in most of their compounds, the representative elements achieve noble gas configuration
S=N-A
S = # of shared valence e-
exceptions will be discussed later
N= # of valence e- needed to acheive octet
except H (2 e-), Be (4 e-) and B (6 e-)
A= # of valence e- available
H2O
N= (2*2) + (8*1) = 12
A = (2*1) + (6*1) = 8
S = 4

10. Octet Rule and Lewis Formulas for Molecules
octet rule - in most of their compounds, the representative elements achieve noble gas configuration
S=N-A
S = # of shared valence e-
exceptions will be discussed later
N= # of valence e- needed to acheive octet
except H (2 e-), Be (4 e-) and B (6 e-)
A= # of valence e- available
H2O
N= (2*2) + (8*1) = 12
A = (2*1) + (6*1) = 8
S = 4 .. .. .. ..
O H H

11. Writing Lewis Structures
1) Symmetrical Skeleton
least electronegative element is central - CS S C S
oxygen does not bond to oxygen (exept in peroxide and superoxides)
ternary acids the H is usually bonded to the oxygen H O N O
exception H3PO3 and H3PO2
2) Calculate N, A and S
SO N = 5*8 = A = 6*5 + 2 = 32 S = = 8
3) Place the S (shared) electrons between atoms
use double and triple bonds only when necessary
4) Place additional electrons into the skeleton as lone pairs to fill the octet of every atom except H (2 e-), Be (4 e-) and B (6 e-) 2- O
H O S O H O
O S O
H2SO4
SO42- 2- O
O S O

12. CO2
Step 1:

13. CO2
Step 1:
Step 2: N = 3*8 = A = 2*6 + 4 = 16 S = = 8

14. CO2 Step 1: Step 2: N = 3*8 = 24 A = 2*6 + 4 = 16 S = 24-16 = 8

15. CO2 Step 1: Step 2: N = 3*8 = 24 A = 2*6 + 4 = 16 S = 24-16 = 8

16. CO2 Resonance Structures Step 1:
Step 2: N = 3*8 = A = 2*6 + 4 = 16 S = = 8
Step 3:
Step 4:
Resonance Structures

17. Resonance Structure of CO32-

18. Resonance Structure of CO32-
N= 4*8 = A=1*4 + 3*6 + 2 = S=8 C O O

19. Resonance Structure of CO32-
N= 4*8 = A=1*4 + 3*6 + 2 = S=8 C O O

20. Resonance Structure of CO32-
N= 4*8 = A=1*4 + 3*6 + 2 = S=8 C O O 2-

21. Limitations to the Octet Rule
Electron Deficient
BeCl3
N=4+(2*8)=20
A=2*7 + 2 =16
S=4
BF3
N=6+(3*8)=30
A=3*7 + 3 =24
S=6
Cl Be Cl
Radicals

22. Expanded Valence Shell
(hypervalent)
PF5 F
N=6*8=48
A=5+(5*7)=40
S=8
S has to be equal to 10 F F P F F
SF4
N=5*8=40
A=6+(4*7)=34
S=6
S has to be equal to 8 F F S F F