C OVALENT C OMPOUNDS
C OVALENT C OMPOUNDS
1.
Usually soft and squishy
2.
Not soluble in water
3.
Does not conduct electricity
4.
Low melting points
5.
Low boiling points
T WO T YPES
OF
B ONDS

Ionic: Electrons are transferred

Covalent: Electrons are shared

Non-polar covalent: equally shared

Polar Covalent: unevenly shared
N AMING C OVALENT C OMPOUNDS
NAMING COMPOUNDS
Nonmetal – Nonmetal
USE PREFIXES!
1.
Change the ending of the second
word to -ide
2.
No mono on the first word
3.
Drop any double vowels
C OVALENT P REFIXES
Number of Atoms
1
Prefix
Mono-
2
3
4
DiTriTetra-
5
6
7
PentaHexaHepta-
8
9
OctaNona-
10
Deca-
THE PREFIX TELLS YOU HOW
MANY ATOMS YOU HAVE!
NO CRISS CROSS!!!!
E XAMPLES
1.
CO
1. Carbon Monoxide
2.
CO2
2. Carbon Dioxide
3.
SO2
3. Sulfur Dioxide
4.
SO3
4. Sulfur Trioxide
5.
N2H4
5. Dinitrogen Tetrahydride
6.
N2O3
6. Dinitrogen Trioxide
E XAMPLES
1.
disilicon hexafluoride
1. Si2F6
2.
tricarbon octachloride
2. C2Cl8
3.
phosphorus pentabromide
3. PBr5
4.
nitrogen monoxide
4. NO
5.
selenium difluoride
5. SeF2
6.
dihydrogen monoxide
6. H2O
EMPIRICAL AND
MOLECULAR FORMULAS
Define Empirical Formula:
A chemical formula that gives the
simplest whole-number ratio of the
elements in the formula.
Which of the following is an empirical formula?
CO2
C2O4
Fe2Cl6
FeCl3
Define Molecular Formula:
A chemical formula that gives the
actual number of the elements in the
molecular compound.
For the following molecular formulas, write the
empirical formula:
Molecular:
C2H4
C6H12O6
C9H21O6N3
Empirical:
L EWIS S TRUCTURES
L EWIS S TRUCTURES FOR
C OMPOUNDS

The pair of dots between two symbols
represents the shared pair.


How many shared pairs does each fluorine have
below?
An unshared pair, also called a lone pair, is
a pair of electrons that is not involved in
bonding and that belongs exclusively to one
atom.
F F
L EWIS S TRUCTURES

The shared pair of electrons is often
replaced by a long dash.
F
F
Each dash represents TWO electrons
W HY SHOULD TWO ATOMS
SHARE ELECTRONS ?
To get a valence of 8 electrons!
+
F
7e-
F
F
7e-
8e-
F
8e-
Lewis structure of F2
single covalent bond
lone pairs
F
F
lone pairs
F
F
single covalent bond
lone pairs
lone pairs
M ULTIPLE C OVALENT B ONDS

double bond:
covalent bond in which two pairs of
electrons are shared between two atoms

shown by two side-by-side pairs of dots
or by two parallel dashes
H
H
C C
H
H
M ULTIPLE C OVALENT B ONDS

triple bond:
covalent bond in which three pairs of
electrons are shared between two atoms

shown by three side-by-side pairs of dots
or by three parallel dashes
S TEPS FOR D RAWING L EWIS
S TRUCTURES
1.
Draw the Lewis Dot diagram for each individual
atom
2.
Count up the number of valence electrons
3.
Connect the atoms together to pair up the
electrons (put atoms that can make the most
connections in the center)
4.
Once all electrons are paired, recount electrons
to double check total valence
P RACTICE
Draw the Lewis Structure for HBr
1.
H
Br
2.
1+7=8
3.
H — Br
4.
2+6=8
B OND P OLARITY
R EVIEW:
W HAT IS ELECTRONEGATIVITY ?
ability of an atom to attract electrons
Which element is the most electronegative?
Fluorine
- Has 7 valence e- and wants 8
H
F
P OLAR
BOND
:
covalent bond with greater electron density
around one of the two atoms
electron poor
region
H
electron rich
region
F
e- poor
H
+
d
e- rich
F
d
1
18
2
13
3
4
5
6
7
8
9
10
11
12
14
15
16
17
W HAT TYPE OF B OND IS IT ?
Electronegativity
Difference
Bond Type
0 to 0.3
Nonpolar Covalent
0.4 to 1.6
Polar Covalent
 1.7
Ionic
Increasing difference in electronegativity
Nonpolar
Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-
Classify the following bonds as ionic, polar covalent,or
covalent:
Cs to Cl
Cs – 0.7
Cl – 3.0
3.0 – 0.7 = 2.3
Ionic
H to S
H – 2.1
S – 2.5
2.5 – 2.1 = 0.4
Polar Covalent
N – 3.0
3.0 – 3.0 = 0
Nonpolar Covalent
Cl to N
Cl – 3.0
I NTERMOLECULAR F ORCES
Intermolecular forces:
attractive forces between molecules.
Intramolecular forces:
attractive forces within a molecule (the bonds)
Intermolecular
Forces
Intramolecular
Forces
Intramolecular
Forces
intramolecular forces are much stronger than
intermolecular forces
D IPOLES

What is a dipole?

A polar molecule

Uneven sharing of electrons so
there is a separation of charge
D IPOLE -D IPOLE F ORCES

Attraction between two polar molecules
—
+
—
+
H YDROGEN B ONDING

Special type of Dipole – Dipole

Attraction between:
Hydrogen and Nitrogen/Oxygen/Fluorine
D IPOLE – I NDUCED D IPOLE

Electrons shift
toward
positive end
of dipole
Attraction between one polar and one
nonpolar molecule
—
—
+
+
—
+
L ONDON D ISPERSION F ORCES

Attraction between two nonpolar molecules
Electrons
become
uneven and
form a dipole
—
+
—
+
S TRENGTH
OF
IMF

Hydrogen Bond

Dipole – Dipole

Dipole – Induced Dipole

London Dispersion Forces
strongest
weakest
W HAT
DOES
IMF

Viscosity

Surface Tension

Cohesion/Adhesion

Boiling Point
EFFECT ?
V ISCOSITY

Measures a fluid’s resistance to flow
Stronger IMF  Higher Viscosity
S URFACE T ENSION

result of an imbalance of forces at the
surface of a liquid.
Stronger IMF  Higher Surface Tension
A DHESION

AND
C OHESION
Cohesion:
intermolecular attraction between like molecules

Adhesion:
intermolecular attraction between unlike molecules
Adhesion
Cohesion
B OILING P OINT

Point at which liquid particles escape the
surface of the liquid into the gas phase
Stronger IMF  Higher Boiling Point