1. Covalent Bonding, Shape and Polarity. Topic 4.2 and most of 4.3

2. LET’S
FIRST
REVIEW
IONIC
BONDING

3. F K In an IONIC bond, electrons are lost or gained,
resulting in the formation of IONS
in ionic compounds. F K

4. K F

5. K F

6. K F

7. K F

8. K F

9. K F

10. + _ K F

11. K F -1 +1 The compound potassium fluoride
consists of potassium (K+) ions
and fluoride (F-) ions

12. K F -1 + 1 potassium fluoride The ionic bond is the attraction
between the positive K+ ion
and the negative F- ion.

13. Covalent Bonds
an electrostatic attraction between a pair of electrons and positively charged nuclei
atoms are sharing valence electrons
this is still in order to achieve an noble gas electron configuration (stable and less energy)
exists where groups of atoms (or molecules) share one or more pair/s of electrons
normally happens between nonmetals

14. Each hydrogen now has the electron configuration of the nearest noble gas- helium

15. Chlorine
forms a
covalent
bond
with
itself
Cl2

16. How
will
two
chlorine
atoms
react? Cl Cl

17. Cl Cl Each chlorine atom wants to
gain one electron to achieve an octet

18. Cl Cl Neither atom will give up an electron
chlorine is highly electronegative (3.2)
What’s the solution – what can they
do to achieve an octet?

19. Cl Cl

20. Cl Cl

21. Cl Cl

22. Cl Cl

23. Cl Cl
octet

24. Cl Cl octet circle the electrons for each atom that completes
their octets

25. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets

26. Cl Cl The octet is achieved by each atom sharing the
electron pair in the middle
circle the electrons for
each atom that completes
their octets

27. Cl Cl This is the bonding pair circle the electrons for
each atom that completes
their octets

28. Cl Cl It is a single bonding pair circle the electrons for
each atom that completes
their octets

29. Cl Cl It is called a SINGLE BOND circle the electrons for
each atom that completes
their octets

30. Single bonds are abbreviatedCl Cl
Single bonds are abbreviated
with a dash
circle the electrons for
each atom that completes
their octets

31. This is the chlorine molecule,Cl Cl
This is the chlorine molecule,
Cl2
circle the electrons for
each atom that completes
their octets

32. O2
Oxygen is also one of the diatomic molecules

33. O
How will two oxygen atoms bond?

34. O
Each atom has two unpaired electrons

35. O

36. O

37. O

38. O

39. O

40. O

41. O Oxygen atoms are highly electronegative.
So both atoms want to gain two electrons.

42. O Oxygen atoms are highly electronegative (3.4)
So both atoms want to gain two electrons.

43. O

44. O O

45. O O

46. O O

47. Both electron pairs are shared.

48. O O
6 valence electrons
plus 2 shared electrons
= full octet

49. O O
6 valence electrons
plus 2 shared electrons
= full octet

50. O O
two bonding pairs,
making a double bond

51. O O =
For convenience, the double bond
can be shown as two dashes.

52. This is the oxygen molecule,=
this is so cool!!
This is the oxygen molecule, O2

53. CCl4 - Covalent MgF2 - Ionic HCl - Covalent Cl [ F ]2– [Mg]2+ Cl H Cl
04/10/99
CCl4 - Covalent
MgF2 - Ionic
HCl - Covalent Cl
[ F ]2–
[Mg]2+ Cl H Cl C Cl
NH3 - Covalent
NaCl - Ionic Cl
[ Cl ]–
[Na] + N H H
H2O - Covalent H
H2 - Covalent O
OH– - Covalent H H H H O H

54. CO2 - Covalent HCl - Covalent Na2O - Ionic O C H Cl [ O ]2– [Na]2+ H
04/10/99
CO2 - Covalent
HCl - Covalent
Na2O - Ionic O C H Cl
[ O ]2–
[Na]2+ H Cl C O
NH3 - Covalent
I2 - Covalent
O2 - Covalent I H N O H N O I
O3 - Covalent H C H C
Al2O3 - Ionic O
[ O ]32–
[Al]23+ O

55. Coordinate Covalent Bonds
occurs when one atom donates its lone pair of electrons in order to be shared between two atoms
should know examples: CO, NH4+ and H3O+

56. Arrow represents the coordinate bond.
Pointing towards the atom that did NOT contribute to the bond

57. Naming covalent compounds
as in ionic bonding, change the ending of the second element to -ide
use prefixes (mono, di, tri, tetra, penta, and hex) in front the element to tell how many atoms are in the formula
exception: do NOT use mono for the first element

58. Dihydrogen Monoxide The Invisible Killer
Dihydrogen monoxide is colorless, odorless, tasteless, and kills uncounted thousands of people every year. Most of these deaths are caused by accidental inhalation of DHMO, but the dangers of dihydrogen monoxide do not end there. Prolonged exposure to its solid form causes severe tissue damage. Symptoms of DHMO ingestion can include excessive sweating and urination, and possibly a bloated feeling, nausea, vomiting and body electrolyte imbalance. For those who have become dependent, DHMO withdrawal means certain death.
Dihydrogen monoxide:
is also known as hydroxyl acid, and is the major component of acid rain.
contributes to the "greenhouse effect."
may cause severe burns.
contributes to the erosion of our natural landscape.
accelerates corrosion and rusting of many metals.
may cause electrical failures and decreased effectiveness of automobile brakes.
has been found in excised tumors of terminal cancer patients.
Contamination Is Reaching Epidemic Proportions.
Quantities of dihydrogen monoxide have been found in almost every stream, lake, and reservoir in America today. But the pollution is global, and the contaminant has even been found in Antarctic ice. DHMO has caused millions of dollars of property damage in the mid-West, and recently California.
Despite the danger, dihydrogen monoxide is often used:
as an industrial solvent and coolant.
in nuclear power plants.
in the production of Styrofoam.
as a fire retardant.
in many forms of cruel animal research.
in the distribution of pesticides. Even after washing, produce remains contaminated by this chemical.
as an additive in certain "junk-foods" and other food products.
Companies dump waste DHMO into rivers and the ocean, and nothing can be done to stop them because this practice is still legal. The impact on wildlife is extreme, and we cannot afford to ignore it any longer!
The American government has refused to ban the production, distribution, or use of this damaging chemical due to its "importance to the economic health of this nation." In fact, the navy and other military organizations are conducting experiments with DHMO, and designing multi-billion dollar devices to control and utilize it during warfare situations. Hundreds of military research facilities receive tons of it through a highly sophisticated underground distribution network. Many store large quantities for later use.

59. CO2 CO N2O3 PO5 S3I2 carbon dioxide carbon monoxide
dinitrogen trioxide
PO5
phosphorus pentoxide
S3I2
trisulfur diiodide

60. Number, length, and strength of bonds
more bonds means stronger
single ⇒ double ⇒ triple
more bonds means shorter length
triple ⇒ d o u b l e ⇒ s i n g l e

63. O2 [NO3] 1- NF3 CO2 [H3O]1+ C2H4 N2 [NH4] 1+ H2Se CO HCN
Draw plausible Lewis dot structures of the following covalent compounds.
note if any bonds are coordinate bonds.
ions need to have [ ] around the actual Lewis structures
O2 [NO3] 1-
NF3 CO2
[H3O]1+ C2H4
N2 [NH4] 1+
H2Se CO
HCN

64. BTW, some atoms form stable molecules without a stable octet
boron
beryllium

65. Resonance Structures more than one Lewis structure can be drawn
often view certain molecules as if they were able to resonate (go back and forth) between two or more different structures
example: NO31- behaves as if it were a blend of the three resonance structures
Single and double bonds have a different length.
However, research shows that all bonds in a resonance molecule have the same length

66. examples should include…

69. Valence Shell Electron Pair Repulsion Theory (VSEPR)
VSEPR Theory YouTube (4:52)
the structure of many molecules is determined mostly by minimizing electron pair repulsions
electrons don’t “want” to be near each other
electron domains are places you would find electrons around a central atom

70. lone pairs (unshared)
pairs of electrons around a central atom NOT in a bond with another atom
have more repulsive force than those found in a bond
bonding pairs (shared)
pairs of electrons being SHARED found in the space between the atoms (can be single, double, or triple bonds)

73. the repulsion between electron domains causes molecular shapes to adjust
electron pairs arrange themselves around the central atom so that they are as far apart from each other as possible
explains the three dimensional shape of a molecule

74. Common VSEPR Shapes (however, there are more)SL
level HL
level

75. VSEPR: Two Electron Pairs
Copyright © Cengage Learning. All rights reserved

76. VSEPR: Three Electron Pairs
Copyright © Cengage Learning. All rights reserved

77. VSEPR: Four Electron Pairs
Copyright © Cengage Learning. All rights reserved

78. Shapes for species with 2, 3, and 4 electron domains on the central atom
2 bonding pairs
0 lone (unshared) pairs
bond angle is 180º
shape is linear

79. 3 Electrons domains 3 bonding pairs 0 lone pairs bond angle 120º
trigonal planar
bent

80. 4 Electron domains 4 bonding pairs 0 lone pairs 3 bonding pairs
bond angle 109.5º
3 bonding pairs
1 lone pair
pushes 3 bonding pairs closer together
bond angle < 109.5º
2 bonding pairs
2 lone pairs
these push 2 bonding pairs even closer together
bond angle < < 109.5º
tetrahedral
trigonal pyramid
bent

84. Drawing 3-D molecules

85. Polarity
shared bonding electrons pairs are sometimes pulled (as in a “tug-of-war”) between atoms
equal sharing is non-polar bond
unequal sharing is polar bond
this often leads to a polar molecule

87. Nonpolar covalent bonds
atoms in the bond pull the shared pair of electrons equally-- so no polarity
always the case in diatomic molecules
HOFBrINCl meaning…
H O2 F Br2 I2 N2 Cl2
memorize these

89. Polar Covalent Bonds
atoms in the bond pull the shared pair of electrons unequally since they have different electronegativities
results in a dipole because it has two poles
use the symbol + or - for areas that are slightly positive or negatively charged

90. or use a vector to point to the negative part of the molecule

94. BF3 has polar bonds yet NOT a polar molecule
there is no “negative end” or “positive end” because of its shape
BF3

95. So why are some molecules polar?
more electronegative atoms have a greater attraction for electrons
a number is assigned to each element to quantify its nucleus’ attraction to a pair of electrons in a shared in bond (example- F is 4.0)
atoms with the higher electronegativity give that “side” of the molecule a slightly negative charge (δ -)
atoms on the “other side” with a lower electronegativity therefore have a slightly positive charge (δ +)

100. covalent, non-polar
covalent, polar
ionic, very, very polar

101. Ionic and covalent are not separate “things” but differences in degree
electronegativty
difference
probable type of bond
0.0 – 0.3
covalent, nonpolar
0.4 – 1.0
covalent, slightly polar
1.1 – 1.8
covalent, very polar
> 1.8
ionic, very, very polar

104. Exercise Arrange the following bonds from most to least polar:
a) N–F O–F C–F
a) C–F, N–F, O–F
b) C–F N–O Si–F
b) Si–F, C–F, N–O
c) Cl–Cl , B–Cl, S–Cl
c) B–Cl, S–Cl, Cl–Cl
The greater the electronegativity difference between the atoms, the more polar the bond.
C-F, N-F, O-F
Si-F, C-F, N-O
B-Cl, S-Cl, Cl-Cl

105. Practice problems
H2O
CO2
CH3Cl
CCl4

106. non-polar
polar

107. Which of the following molecules have a dipole moment (another way to say polar)?
H2O, CO2, SO2, and CH4 O H S O
polar bonds
polar molecule
polar bonds
polar molecule C H C O
polar bonds
nonpolar molecule
polar bonds
nonpolar molecule