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Hybridization
and
Steric Numbers
Hybridization

Some atoms form a different
number of covalent bonds
than the electron
configurations of those atoms
might suggest they should
form.
Hybridization

In general, when we look at
the electron configuration for
an atom, we can infer the type
of bonding that it will
undergo. However, certain
atoms like carbon, beryllium,
and boron, sometimes react
differently than is expected.
Hybridization

Carbon has an electron
configuration of 1s22s22p2.
That indicates that there are 4
electrons in its valence shell.
The 2s orbital is full, and there
are 2 half-filled p-orbitals.
Hybridization

The two half-filled p-orbitals
would suggest that carbon
would form two covalent
bonds. However, scientific
research proves otherwise.
Hybridization

In reality, carbon will
“promote” one of the electrons
in the 2s orbital into the p
orbital, leaving it with 4 halffilled orbitals. This gives
carbon the ability to form 4
covalent bonds.
Hybridization

Chemists describe this unusual
behavior as hybridization.
Hybridization is the
rearrangement of electrons
within the valence orbitals of
atoms during a chemical
reaction.
Hybridization

In carbon, the four half-filled
orbitals all have identical
energies, and each is referred
to as an sp3 hybrid orbital.
3
There are a total of 4 sp
hybrid orbitals, as is illustrated
by adding the superscripts (a
1 is assumed for the s).
Hybridization

Once hybridization has taken
place, any one of the four is
equivalent to any other. All
four orbitals have new bond
characteristics that are
different from the
characteristics of the s and p
orbitals.
Hybridization

Hybridization also occurs in
compounds of beryllium. The
electron configuration if Be is
1s22s2. It would appear to
have no half-filled orbitals with
which to form covalent bonds.
Hybridization

However, Be can form 2
covalent bonds by “promoting”
one of the electrons in the 2s
orbital into the 2p orbital,
giving it 2 half-filled orbitals.
Hybridization

The new half-filled orbitals
formed by Be are referred to
as sp hybrid orbitals. There
are 2 sp hybrid orbitals.
Hybridization

Boron also undergoes a type
of hybridization. The electron
configuration of B is 1s22s22p1.
Boron will promote one of the
2s electrons, giving it 3 halffilled orbitals in its valence
shell, allowing it to form 3
covalent bonds.
Hybridization

This kind of hybridization is
referred to as sp2
hybridization.
Hybridization

Another approach to this
problem is to consider the
steric number. The steric
number is the number of
atoms bonded to the central
atom AND the number of lone
PAIRS of electrons.
Steric Numbers

Steric numbers can be used to
determine the geometry and
the bond angles that would be
formed with the atoms and
the central atom.
Steric Numbers

The steric number is determined
by counting the number of
bonded groups attached to the
central atom and the number of
lone pairs of electrons attached
to the central atom. Note that
steric numbers are determined by
first drawing the Lewis dot
structure of the compound or ion.
Steric Numbers
A steric number of four results in
a tetrahedral arrangement in
three dimensions with bond
angles of 109.5°.
 A steric number of three results
in a trigonal planar arrangement
in three dimensions with bond
angles of 120°.

Steric Numbers

A steric number of two results in
a linear arrangement in three
dimensions with bond angles of
180°.