1. Topic 6
Bonding

2. Topic 6-Bonding
Energy and Chemical Bonds
a. Make bonds-exo (release energy)
b. Break bonds-endo (absorb energy)
BARF
Lewis Dot Revisited for Compounds
a. Ionic Substances
b. Molecular Substances
Octet Rule
Covalent Bonds-sharing of electrons
a. Nonpolar bonds (EN difference = 0)
b. Polar bonds (EN difference is )
Molecular Substances
a. Polar Molecules-asymmetric
b. Nonpolar Molecules-symmetric
SNAP
6. Ionic Bonding (EN difference > 1.7)
Metallic Bonding
Polyatomic Ions
Intermolecular Forces between molecules
a. Hydrogen Bonds
b. Van der Waal Forces aka London Dispersion Forces
c. Molecule-Ion attractions

3. Energy and Chemical Bonds
Break bonds-absorb energy-endothermic
Form bonds-release energy-exothermic
Remember: BARF
B = break bonds
A = absorb energy
R = release energy
F = form bonds
Break bonds-absorb energy =decrease stability
Form bonds-release energy = increase stability
The energy stored in a bond is potential energy

4. Lewis Dot for Molecular Substances
Molecular Substances are covalently bonded
Covalent bonds are found when nonmetals bond to nonmetals
Show the Lewis dot structure for ammonia (NH3)
Element
# of atoms
Valence electrons
Total 5 N 1 5 H 3 1 3
______ 8
You only have 8 electrons to work with. Each element must
have 8 electrons around it except H and He which only have
2 electrons around them
. .
Now each atom has a filled octet x x H . N . H . x
N has 8 valence electrons H
Each H has 2 valence electrons

5. You do whatever it takes to ensure that all atoms have 8 valence electrons except H and He which only need 2 valence electrons
Lets try: H2 I2
CH4
H2O

6. Lets try some that are slightly tricky!
CO2 O2 N2

7. Lewis-Dot for Ionic Compounds
An ionic compound occurs when a metal bonds to a nonmetal
This is a much simpler method
The metal has no valence electrons around it and
The nonmetal has 8 valence electrons around it (unless it is H)
NaCl
Na = metal
Cl = nonmetal ..
[Na]+
[ :Cl:]- ..

8. Calcium Chloride
CaCl2
Ca = metal
Cl = nonmetal .. ..
[:Cl:]-
[Ca]2+
[:Cl:]- .. ..
Sometimes, there will be no brackets around the metal .. ..
[:Cl:]- Ca2+[:Cl:]- .. ..

9. Atoms react by gaining (nonmetals) or losing electrons (metals)
Octet Rule
Atoms react by gaining (nonmetals) or losing electrons (metals)
so as to acquire the stable electron configuration of a noble gas,
usually 8 valence electrons except H and He which has 2 valence electrons
The element with the lower EN (metal) value will always
lose electrons
The element with the higher EN value (nonmetal) will always
gain electrons

10. Covalent Bond
When you hear the word covalent, think molecule and vice-versa
Always between NM-NM
2 types of covalent bonds
1. Nonpolar Covalent-
Equal SHARING of electrons
EN difference is 0 so it only occurs when atoms of same element (nonmetals) are bonded to each other or the seven diatomic elements
EN values are on Table S
The seven diatomic elements:
Br2 I2 N2 Cl2 H2 O2 F2
Or anytime the same element (nonmetal) is bonded to each other
C-C

11. 2. Polar Covalent Bond-
Unequal SHARING of electrons
EN difference is between
The element with the higher EN value will have the electrons most
of the time
EN values are on Table S
The greater the EN difference, the more polar the bond is
The smaller the EN difference, the less polar the bond is
Covalent substances NEVER conduct a current

12. when in solution-mixed with water (aq)
Ionic Bonding
The TRANSFER of electrons from an atom with low EN to an atom with high EN
Always occurs between a metal and a nonmetal
EN difference is 1.7 or greater
Ionic substances conduct a current either when melted (fused) or
when in solution-mixed with water (aq)
NaCl (s) – does not conduct
NaCl (l) – does conduct
NaCl (aq) – does conduct

13. Polyatomic Ions (PAIs)
Table E
Compounds with PAIs have both ionic and covalent bonds
Within the PAI, there are covalent bonds and whatever
the PAI bonds to is an ionic bond
NH4Cl
Look on Table E for the PAI
It is NH4
So between N and H there are covalent bonds
Between NH4 and Cl are ionic bonds

14. Polar vs. Nonpolar Molecules
When they are talking about molecules (not bonds) they are asking
you if the molecule shape has symmetry or not.
If it is a nonpolar molecule, it has symmetry
If it is a polar molecule, it is asymmetric (no symmetry)
Think SNAP
symmetry S N A P
nonpolar
asymmetric
polar

15. + Polar Molecules are referred to as dipoles Dipole-
A molecule that has two poles, or regions with opposite
charges
The electrons move to the end
with the higher EN value, giving
it a negative side.
The side with the lower EN value is
now positive
____
EN = 3.4
EN = 2.2 +
Nonpolar molecules cannot be dipoles

16. You must KNOW the following structures
Nonpolar bonds (EN diff. = 0)
Nonpolar molecule (symmetry)
Linear shape
Nonpolar bonds (EN diff. = 0)
Nonpolar molecule (symmetry)
Linear shape

17. CO2 N2
Polar bonds (EN diff. =.8)
Nonpolar molecule (symmetry)
Linear shape
Nonpolar bonds (EN diff. = 0)
Nonpolar molecule (symmetry)
Linear shape

18. NH3
H2O
Polar bonds (EN diff = .8)
Polar molecules (asymmetric)
Pyramidal shape
Polar bonds (EN diff. = 1.4)
Polar molecule (asymmetric)
Bent shape

19. CH4
Polar bonds (EN diff. = .4)
Nonpolar molecule (symmetry)
Tetrahedral shape

20. If a molecule is:
1. Nonpolar, it has symmetry and equal charge distribution
2. Polar, it has no symmetry and unequal charge distribution
Nonpolar molecule = symmetry = equal charge distribution
Polar molecule = asymmetric = unequal charge distribution
Again….DO NOT confuse polar/nonpolar molecules with
polar/nonpolar bonds.

21. Metallic Bonds
Between metal atoms
The force of attraction that holds metals together; it consists
of the attraction of free-floating valence electrons for positively
charged metal ions
“Sea of mobile electrons”
Ex.: Cu, Au, Ag, Sn, Pb, Fe, Ni

22. A covalent bond in which one atom contributes both bonding
Coordinate Covalent Bond
A covalent bond in which one atom contributes both bonding
electrons

24. All of the atoms are covalently bonded to each other
Network Solid
All of the atoms are covalently bonded to each other
All the properties of covalent substances except they are
very hard and have extremely high bp and mp
Examples of network solids are
Diamond (C)
Quartz (SiO2)
SiC

25. Diamond encrusted car
diamonds
quartz
Silicon carbide

26. Intermolecular Forces
Forces between molecules not atoms
Hydrogen bonds-
Very weak forces except when hydrogen
bonds to F, N or O
When H bonds to F, N or O, those compounds have unusually
high boiling points
What is so unusual about F, O and N?
They have a small atomic radius and high electronegativty

27. Van der Waals forces
Between nonpolar molecules (symmetry)
Explains why gases can be liquefied
Increase in strength as molecules get bigger
Increase in strength as distance between molecules decreases
Aka London Dispersion Forces
Dipole-Dipole Attraction
Occurs between polar molecules (asymmetric)
The – end of one dipole is attracted to the + end of
the other dipole

28. Molecule-Ion Attraction
Occurs between a covalent substance (H2O) and an ionic compound
NaCl (aq)
NaCl is the ionic compound
aq = water (covalent substance
Water is a dipole. The – end (O) is attracted to the + ion (Na)
The + end (H) is attracted to the –ion (Cl)

29. Summary
Covalent Bonds-sharing of electrons
Nonpolar covalent bond-electronegativity difference of 0
Polar covalent bond-electronegativity difference
Ionic Bonds-transfer of electrons
Electronegativity difference of 1.7 or greater
Metallic Bonds-sea of mobile electrons

30. Metallic-sea of mobile e (M-M) Boiling pt High Low high
Summary of Ionic/Covalent/Metallic Substances
Ionic-transfer
(M-NM)
Covalent-share
(NM-NM)
Metallic-sea of mobile e
(M-M)
Boiling pt
High
Low
Except for network solids
high
Melting
Conductivity
Only as a
(L) or (aq)
Never
Only as
a (s) or
(L)

31. Why do some substances conduct heat or electricity
while others do not?
Why do some compounds only conduct
in one phase and not other phases?
The answer:
Why do some substances conduct?
Free moving charged particles
Why do some substances not conduct?
No free moving charged particles

32. I do not care what type of substance it is:
Ionic, Covalent or Metalic
I do not care what phase of matter it is in:
Solid, Liquid or Gas
If it conducts-free moving charged particles
If it does not conduct-no free moving charged particles

33. Why are some solid substances soft and others hard?
Hard-strong attractive forces between particles
Soft-weak attractive forces between particles