Chemical Bonding
In compounds, atoms are held together by forces
known as chemical bond.
Electrons play a key role in chemical bonding.
An electron in an atom can be characterized by
quantum numbers.
1. Principal quantum number (n)
n = 1, 2, 3, ….
K L M
2. Orbital quantum number (l)
l = 0, 1, 2, 3, …. n-1
s p d f
3. Magnetic quantum number (ml)
-l, o, +l
4. Electron spin:
+ 1/2 or – 1/2
Shorthand notation to designate electron
configuration:
spdf notation:
8O
13Al
1s2 2s2 2p4
1s2 2s2 2p6 3s2 3p1
O
Al
1s
2s
2p
1s
2s
2p
inner-shell electrons
Kernel of the atom
Al
Lewis symbol
orbital diagram:
3s
3p
outer-shell electrons
Valence electrons
Lewis theory:
1. Electrons of the outermost (valence) electron shell play a
fundamental role in chemical bonding.
2. Chemical bonding may result from the transfer of one or more
electrons from one atom to another. This type of bond known as
ionic.
3. Chemical bonding may result from a mutual sharing of
electrons between atoms. This bond type called covalent.
4. Transfer or sharing of electrons results in noble gas
configuration, that is, often an octet.
First ionization energy
Ionic bond:
Electron affinity
Na
Cl
Na+
Na
+
Cl
Na+ +
Cl
Cl-
1. Ionic bond results from the transfer of electrons between a metal
and a nonmetal.
2. The nonmetal atom gains a sufficient number of electrons to
produce an anion with noble gas electron configuration.
3. In solid state an enormous number of in cluster together
into a crystalline solid.
4. Formula unit: the smallest collection of ions that is electrically
neutral.
Covalent bonding involves sharing of electrons
H
+
Cl
H Cl
Single covalent bonding:
H
+
H
Cl
+ Cl
H H
Cl Cl
or H
H
Nonpolar: DE.N. < 0.6
Multiple covalent bonding:
N
N
O
O
N
N
O
O
NH3 + H+
NH4+
H
H
H
H
N + H+
Polar:
0.6 < DE.N < 2.1
Ionic:
DE.N > 2.1
H +
N
H
H
Coordinate
covalent
bond