1. Molecular Compounds and their Covalent Bonds
the next new chemistry idea!

2. Molecular Compounds who - nonmetallic elements
how - shared electrons between atoms
not always equally
why - each atom wants a complete octet
what type of bond ≡ covalent bond
where - majority of biological molecules

3. Covalent bonds – strong vs strong
Attractive forces between atoms in molecules
Usually involving nonmetal elements in groups 4A, 5A, 6A, and 7A
Involve sharing electrons so every atom gets to be “noble” for a bit

4. Single Covalent Bonds
It’s all about sharing electrons H2
1S S1

5. Covalent bond shorthand
Single covalent bonds (1 shared e pair)
H : H Lewis dot configuration
H - H structural formula
molecular shape

6. Lewis Dot Rules for Molecular Compounds
Look up the Z’s of each atom
Determine # of valence electrons for each atom
Write element symbols and place 1 e pair between the central and the adjacent atom
Place remaining e pairs so that there are 4 e pairs around each outer atom
Make sure total number of valence electrons are accounted for, if not. . .
Place any extra e’s around central atom

7. Case 1: Molecules with a Single Covalent Bond
Br2

8. Case 2: Molecules with Single Covalent Bonds
CH4
IN this case one of the 2s carbon orbitals is promoted to a p orbital

9. Side bar – Who’s in the Middle?
atom with a subscript of “1” or
atom with the smallest subscript

10. Case 3: Molecules with Single Covalent Bonds
NH3
IN this case one of the 2s carbon orbitals is promoted to a p orbital

11. Practice – Single Covalent Bonds
PCl3
H2O
OF2

12. then there’s . . . Double and Triple Covalent Bonds
Some atoms share more than one pair of electrons
Double covalent bonds share 2 pairs of electrons
Triple covalent bonds share three pair of electrons

13. Double Covalent Bonds O2
CO2

14. Double and Triple Bonds
C2H4
C2H2

15. Coordinate Covalent Bonds
One atom donates both bonding electrons CO
NH4+1
Most polyatomic ions contain covalent and coordinate covalent bonds

16. Covalent Compound Practice
SO2
SO3
N2O
H3O+
SO3-2

17. Which Bond – When? it’s all about Electronegativity
Definition – the “grabbiness” of an atom for an electron;
the more grabby, the greater the EN value
ex, F = 4.0; Na = 0.9; C = 2.5; H = 2.1; O = 3.5
Use EN difference to determine bond type
Ionic bonds – EN difference ≥ 1.5
Covalent Bonds - EN Difference < 1.5

19. Covalent Bond Polarity
Nonpolar Covalent bonds – equal sharing
0.0 < Electronegativity difference < 0.4
Polar Covalent Bond – unequal sharing
0.4 < Electronegativity difference < 1.5
Line becomes arrow from positive to negative

21. Practice – Which Bond Type?
Chemical Bond
EN difference
I, PC, NPC
H-F
|2.1 – 3.98|= 1.88 I
C-H
|2.55 – 2.1|= 0.45
NPC
Cl-O
K-Cl
O-H
C-O
S-O
Br-Br

22. Molecular Polarity

23. Molecular Polarity examples
CH4
CH3Cl
HCl
NH3
H2O

24. Ionic cf Covalent Compounds

25. Ionic cf Covalent Compounds
Property
Ionic Compound
Molecular Compound
Representative Unit
Bond Type
Element Groups
Physical State
Melting Point
Solubility in water
Electrical Conductivity