The document discusses hybrid orbitals and how they relate to the geometry around carbon atoms. It explains that carbon forms sp, sp2, and sp3 hybrid orbitals for molecules with 2, 3, and 4 electron pairs around carbon respectively. This determines the valence shell electron pair repulsion (VSEPR) geometry and bond angles, leaving 0-2 unhybridized p orbitals available for pi bonding.
2. Valence Electrons
Valence electrons are usually the
s and p electrons in the
outermost unfilled shell of an
atom.
For main group elements, the
number of valence electrons is
the same as the group number.
Carbon is in group IV and has
four valence electrons.
3. Valence Electrons
Another way to find the valence
electrons is to determine the electronic
configuration of the atom.
Carbon has 6 electrons. The electrons
fill the lowest energy orbital first and
work their way up (the aufbau
principle).
You might remember the orbital
energy diagram (next slide).
C: 1s22s22p2
5. Valence Electrons
Since for tests you are not given
an orbital energy diagram but you
are given a periodic table, be able
to use the periodic table to
determine an electronic
configuration (next slide).
C: 1s22s22p2
8. Orbital Shapes
p orbitals have two lobes. There
are three p orbitals and they are
perpendicular to each other.
9. Valence Bond Theory
Valence bond theory says that
bonds between atoms are formed
by the overlap of atomic orbitals.
If we use the 2s and 2p orbitals
of C to explain its bonding in
methane (CH4), we would predict
90° bond angles.
The bond angles are 109.5°.
10. VSEPR Theory
Valence shell electron pair
repulsion (VSEPR) theory says
that the geometry around an
atom is determined by the
number of its electron pairs and
the fact they want to be as far
from each other as possible.
4 electron pairs, tetrahedral
geometry, 109.5° bond angles
11. sp3 Hybrid Orbitals
1s
2s
2p
Orbital
energy
Energy is used to promote
one 2s e- to the empty 2p
orbital.
Carbon has four e- available for bonding.
However, the orbitals containing the four e-
must first be mixed to form four orbitals with
the same energy.
15. Figure 11.9 The s bonds in
ethane(C2H6).
both C are sp3
hybridized s-sp3 overlaps to s
bonds
sp3-sp3 overlap to form a s
bond relatively even
distribution of
electron density
over all s bonds
16. Valence Bond Theory and
Double Bonds
In Ethene, there are three
electron pairs around each C
atom. VSEPR theory says the
geometry is trigonal planar and
the bond angles are 120°.
A different set of hybrid orbitals
must be present. They are
formed from the 2s orbital and
two of the 2p orbitals.
17. Ethene is C2H4 and has a Lewis structure of:
1s
sp2
2p
orbital energy diagram for C
One 2p orbital remains
unhybridized.
H
H
H
H
C = C
All of the atoms of ethene lie
in a single plane. Bond
angles are 120°.
sp2 Hybrid Orbitals
Trigonal planar VSEPR geometry sp2 hybrid orbitals.
E
19. Ethene
H
H
H
H
C = C
Valence Bond Theory and
Double Bonds
1. Each C – H bond is a σ bond formed from the
overlap of a C sp2 orbital with the H 1s orbital.
2. One of the C – C bonds is a σ bond formed from the
overlap of C sp2 orbitals.
σ bonds are formed
from the end-to-
end overlap of
orbitals.
20. Ethene
H
H
H
H
C = C
3. The second C – C bond is a π bond formed from the
overlap of the unhybridized C 2p orbitals.
Valence Bond Theory and
Double Bonds
21. Ethene
H
H
H
H
C = C
The overlap in a π bond is side-to-side (NOT
end-to-end like in σ bonds).
π Bonds
23. Valence Bond Theory and
Triple Bonds
In Ethyne, there are two electron
pairs around each C atom. VSEPR
theory says the geometry is linear
and the bond angles are 180°.
A third set of hybrid orbitals must
be present. They are formed from
the 2s orbital and one of the 2p
orbitals.
24. Ethyne is C2H2 and has a Lewis structure of:
1s
sp
2p
orbital energy diagram for C
Two 2p orbitals remain
unhybridized.
H - C ≡ C - H All of the atoms of Ethyne lie in a single line.
E
Linear VSEPR geometry sp hybrid orbitals.
sp Hybrid Orbitals
26. Valence Bond Theory and
Triple Bonds
Ethyne H - C ≡ C - H
1. Each C – H bond is a σ bond formed from the
overlap of a C sp orbital with the H 1s orbital.
2. One of the C – C bonds is a σ bond formed from the
overlap of C sp orbitals.
27. Ethyne H - C ≡ C - H
3. The other two bonds are π bonds formed from
the overlap of the C 2p orbitals.
Valence Bond Theory and
Triple Bonds
