1. Ch. 6 Bonding
6.2 Covalent Bonding

2. Molecular Compounds
molecule: neutral group of atoms held together by covalent bonds
molecular compound: compound whose simplest unit is a molecule

3. Formulas
chemical formula: tells the number of each type of atom in a compound
molecular formula: tells the number of each type of atom in a molecular compound
ex. H2O, Cl2, C6H12O2

4. Molecular Compounds
diatomic molecule: a molecule containing only 2 atoms
usually refers to 2 of the same atoms
ex: O2, Br2, F2, etc.
7+1 rule

5. Formation of Covalent Bond

6. Formation of Covalent Bond
two nuclei and two electron clouds repel each other creating an increase in PE
approaching nuclei and electron clouds are attracted to each other to create a decrease in PE

7. Formation of Covalent Bond
a distance between the nuclei is reached in which
repulsion and attraction forces are equal
potential energy is at the lowest point possible
at the bottom of the curve on PE graph

8. Covalent Bonds Bond Length
distance between two bonded atoms at their lowest PE
average distance since there are some vibrations
measured in pm (1012 pm = 1 m)
stronger the bond, shorter the bond

10. Covalent Bonds Bond Energy
energy is released when atoms combine because they have lower PE
the same amount of energy must be used to break the bond and form neutral isolated atoms
stronger bond, higher bond energy
average since varies a small amount based on atoms in entire molecule
in kJ/mol

12. Octet Rule
representative elements can “fill” their outer energy level by sharing electrons in covalent bonds
Octet Rule- a compound tends to form so that each atom has an octet (8) of electrons in its highest energy level by gaining, losing or sharing electrons
Duet Rule- applies to H and He

13. Octet Rule Less than 8: More than 8: Boron: 6 in outer energy level
anything in 3rd period or heavier
because may use the empty d orbital
ex: S, P, I

14. Electron Dot Diagrams a way to show electron configuration
identifies the number and pairing of valence electrons to show how bonding will occur
write the noble gas notation
identify the number of valence
identify how many are paired and how many are alone
do not go by Figure 6-10

15. N Example Nitrogen Sulfur 1s2 2s2 2p3 5 valence 2 are paired
3 are alone
Sulfur
1s2 2s2 2p6 3s2 3p4
6 valence
4 paired (2 pairs)
2 are alone N

16. Lewis Structures like dot diagrams but for entire molecules
atomic symbols represent nucleus and core electrons and dots or dashes represent valence electrons
unshared electrons: (lone pairs) pair of electrons not involved in bonding written around only one symbol
bonding electrons: written in between 2 atoms as a dash

17. Types of Bonds single- sharing of one pair of electrons
weakest, longest
double- sharing of 2 pairs of electrons
stronger and shorter
triple- sharing of 3 pairs of electrons
strongest and shortest
multiple bonds include double and triple bonds

18. Drawing Lewis Structures
find the number of valence electrons in each atom and add them up
draw the atoms next to each other in the way they will bond
add one bonding pair between each connected atoms
add the rest of the electrons until all have 8 (consider exceptions to octet rule)

19. H H C Cl CH3Cl Example 1 methyl chloride C: 4 x 1 = 4 H: 1 x 3 = 3
Cl: 7 x 1 = 7
total = 14 electrons
carbon is central H
H C Cl
duet
octet
duet
octet
duet H
H C Cl

20. H N H H NH3 Example 2 ammonia N: 5 x 1 = 5 H: 1 x 3 = 3 total = 8
N is central
Example 2
H N H H

21. Example 3 N2
nitrogen gas
N: 5 x 2 = 10
10 electrons
N N
N N

22. H C H O Example 4 CH2O formaldehyde C: 4 x 1 = 4 H: 1 x 2 = 2
O: 1 x 6 = 6
total = 12
C is central
H C H O

23. O O O O O O Example 5 O3 ozone O: 6 x 3 = 18 two completely equal
arrangements
the real structure
is an average of these two
where each bond is sharing 3 electrons instead of 4 or 2
O O O
O O O

24. O O O O O O Resonance Structures
resonance – bonding between atoms that cannot be represented by Lewis structure
show all possible structures with double-ended arrow in between to show that electrons are delocalized
O O O
O O O

25. NO31-
N: 5 x 1 = 5
O: 6 x 3 = 18
total = = 24
Example 6

26. Covalent Network Bonding
a different type of covalent bonding
not specific molecules
lots of nonmetal atoms covalently bonded together in a network in all directions
example:
diamond
silicon dioxide
graphite