CHAPTER 7
Chemical Bonding
1.
2.
3.
4.
5.
6.
7.
Ionic Bonding
Covalent Bonding
Lewis Dot Formulas of Atoms
Lewis Formulas for Molecules & Polyatomic Ions
The Octet Rule
Resonance
Dipole Moments
1
Introduction
Ionic bonding results from electrostatic
attractions among ions, which are formed
by the transfer of one or more electrons
from one atom to another.
o Covalent bonding results from sharing
one or more electron pairs between two
atoms.
o
2
Ionic compounds
Covalent compounds
usually solids with high melting points,
typically > 400 oC
gases, liquids, or solids with low
melting points, typically < 300 oC
generally soluble in polar solvents
generally insoluble in polar solvents
generally insoluble in nonpolar solvents generally soluble in nonpolar solvents
generally conduct electricity in molten
solids and liquids
generally do not conduct electricity in
molten solids and liquids
generally conduct electricity in aqueous
solutions
are poor conductors of electricity in
aqueous solutions
are formed between elements with large
differences in electronegativity
are formed between elements with
similar electronegativities
3
Formation of Ionic Compounds
1s
Li ↑↓
F ↑↓
2s
↑
↑↓
2p
↑↓↑↓↑
These atoms form ions with these configurations.
Li+ ↑↓
F- ↑↓
same configuration as [He]
↑↓ ↑↓ ↑↓ ↑↓
same configuration as [Ne]
4
Formation of Ionic Compounds
z
The Li+ ion contains two electrons, same
as the helium atom.
• Li+ ions are isoelectronic with helium.
z
The F- ion contains ten electrons, same
as the neon atom.
• F- ions are isoelectronic with neon.
z
Isoelectronic species contain the same
number of electrons.
5
Formation of Ionic Compounds
4s
4p
K [Ar] ↑
Br [Ar] ↑↓ ↑↓ ↑↓ ↑ and the d electrons
The atoms form ions with these electronic
structures.
4s
K+
Br-
4p
same configuration as [Ar]
↑↓ ↑↓ ↑↓ ↑↓
same configuration as [Kr]
6
Formation of Ionic Compounds
z
z
Cations become isoelectronic with the
preceding noble gas.
Anions become isoelectronic with the
following noble gas.
7
Formation of Ionic Compounds
8
Formation of Ionic Compounds
• Notable exceptions are BeCl2, BeBr2,
which are covalent compounds.
z
and BeI2
One example is the reaction of Be and F2.
Be(solid) + F2(gas) →BeF2(gas)
9
Formation of Ionic Compounds
Be(solid) + F2(gas) →BeF2(gas)
2s
2p
Be [He] ↑↓
F [He] ↑↓ ↑↓ ↑↓ ↑
2s
2p
→ Be2+
→ F- ↑↓ ↑↓ ↑↓ ↑↓
10
Formation of Ionic Compounds
z
Draw the electronic configurations for Li, O,
and their appropriate ions.
z
Li(solid) + O2(gas) Æ Li2O(solid)
2s
2p
Li [He] ↑
O [He] ↑↓ ↑↓ ↑ ↑
2s
2p
→ Li1+
→ O2- ↑↓ ↑↓ ↑↓ ↑↓
11
Formation of Ionic Compounds
z
Draw the electronic representation of Ca, N,
and their ions.
3 Ca (s) + N 2(g) → Ca 3 N 2 (s)
Ca [Ar]
N [He]
4p
4s
4p
4s
↑↓
→ Ca2+
2s
2p
2s
2p
↑↓ ↑ ↑ ↑ → N3- ↑↓ ↑↓ ↑↓ ↑↓
12
Formation of Ionic Compounds
(q )(q )
F∝
+
z
z
−
Ionic compounds form
d2
extended three dimensional
where
arrays of oppositely charged
F = force of attraction between ions
ions.
q = magnitude of charge on ions
Ionic compounds have high
melting points because the d = distance between center of ions
coulomb force, which holds
ionic compounds together,
is strong.
13
Formation of Covalent Bonds
z
This figure shows the potential energy of an H2
molecule as a function of the distance between the
two H atoms.
14
Formation of Covalent Bonds
z
Representation of
the formation of an
H2 molecule from H
atoms.
15