CHAPTER 6: ATOMIC STRUCTURE AND CHEMICAL BONDS
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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