Transcript CHAPTER 6: ATOMIC STRUCTURE AND CHEMICAL BONDS

Chemical Bonding
Recall: Electron dot diagrams are
for predicting bonding
Dots are written on 4 sides of the symbol
a. One dot - single electron
b. Two dots – electron pair
Make sure your dots are bold and pairs
look paired!
Dot Diagram Examples:
Group 1A: Alkali Metals
Lithium
Group 6A: Chalcogens
Sulfur
Group 7A: Halogens
Chlorine
What is a bond?

Often shown like:

Chemical bond: The
force that holds two atoms
together.
It will always be an
electrostatic attraction
between oppositely
charged species.
Why do atoms bond?
To increase stability, but…
 Bonding is not always favored
 What types of things confer stability?

 Full
or empty Valence Shells
 Paired Electrons
Bonding Types:
 Metallic
 Ionic
 Covalent
IONIC BONDS
Characterized by: Transfer of electrons.
1. Atoms no longer neutral because they have lost or
gained e-, now called ions.
2. Ionic bond: Electrostatic attraction between
oppositely charged ions
a. Ex: Sodium chloride is made of sodium ions
and chloride ions.
b. Compound: 2 or more atoms chemically
bonded
3. Some atoms can gain or lose more than one e-
IONIC BONDING with
SODIUM AND CHLORINE
Properties of Ionics:





High MP/BP
Solids at room temp.
Arrange themselves into a 3-D alternating
pattern called a crystal lattice
Most dissolve readily in water (aqueous
solution)
Conductivity:
 Solids
do not conduct
 Liquids do conduct
 Aqueous solutions conduct (Term: Electrolyte!)
COVALENT BONDS
Characterized by electron sharing.
1. Covalent Bond: The attraction of each
nucleus for a shared pair of electrons.
2. Atoms sharing electrons form a neutral
particle called a molecule.
Covalently bonded compounds are called
molecular compounds.
3. No electrons are gained or lost.
4. Multiple bonds:


Two pairs of electrons are shared in a double bond.
Three pairs of electrons are shared in a triple bond.
Examples:
COVALENT CHLORINE BOND
COVALENT HYDROGEN BOND
Properties of Covalents:
Lower MP/BP
 Solids, liquids or gases at room temp.
 Solids often soft & waxy
 Generally do not dissolve in water
 Conductivity:

 No!
Not in any state of matter or in aq
solution
Electronegativity and Bond Type
I’m not stealing, I’m sharing unequally
All bonds share – equally or unequally!
H2
H H
covalent
(non-polar)
HCl
H Cl
+
–
polar covalent
LiCl [Li]+[
–
+
ionic
Note:  indicates “partial charge”
Cl ]–
Ionic or Covalent?
Look at electronegativity difference (∆EN):
0
to 0.29 – Non-polar Covalent

Perfect sharing of e-
 0.30
to 1.69 – Polar Covalent
Sharing is unequal
 Positive & Negative ends to the bond

 1.70

and up – Ionic (Not covalent, but extremely polar!)
Sharing so unequal we say transfer occurs
Use the periodic table that I handed
out to find electronegativities:
Ionic, polar covalent, or nonpolar
covalent?

S and H
2.58-2.20=0.38
polar covalent

Cl and Ca
3.16-1.00=2.16
ionic

S and Cs
2.58-0.79=1.79
ionic

Cl and Br
3.16-2.96
nonpolar covalent
POLAR AND
NONPOLAR BONDS
A polar bond occurs when electrons are
unevenly shared.
All bonds with ∆EN of 0.30 or higher
are polar, regardless of whether they
are ionic or covalent!
Arrange in order of decreasing
bond polarity:
H-H,
O-H,
Cl-H,
S-H,
2.20-2.20
3.44-2.20
3.16-2.20
2.58-2.20
0.96
0.38
0
1.24
F-H
3.98-2.20
1.78
F-H > O-H > Cl-H > S-H > H-H