Video Transcript
By considering the shape of the
individual units that make up the macromolecule in the diagram, which type of
hybridization is occurring in the carbon atoms of graphene? (A) sp3d2, (B) sp2, (C) sp3d, (D)
sp3, or (E) sp.
Hybridization, or more specifically
orbital hybridization, is the concept of mixing atomic orbitals into new and
different types of hybrid orbitals, where atomic orbitals are mathematical functions
that describe the location and wave-like behavior of an electron in an atom. The simplest and lowest-energy
atomic orbital is the 1s atomic orbital. This is followed by the 2s atomic
orbital and 2p atomic orbitals. So these atomic orbitals can be
mixed or hybridized to form new hybrid orbitals. Other atomic orbitals, such as d
orbitals or f orbitals, can also undergo hybridization. But for simplicity, let’s stick
with s and p.
Let’s look at an example of
hybridization using carbon. Carbon atoms have four electrons in
their outer shell. Two of these electrons are in a 2s
orbital, and the other two electrons are in the 2p orbitals. The hybridization process occurs
when one of the 2s subshell electrons on the bonding carbon atom is promoted or
excited into a vacant 2pz atomic orbital. The bonding carbon atom then has
four unpaired electrons in four different orbitals that can merge together and form
four hybrid sp3-type bonding orbitals. As this type of hybridization
involves 1s orbital and 3p orbitals, it is called sp3 hybridization.
sp3 orbitals have a tetrahedral
shape. This type of hybridization occurs
for carbon atoms in molecules such as methane, which has a tetrahedral shape. The macromolecule in the diagram
doesn’t have this kind of tetrahedral shape. So it must undergo a different type
of hybridization. Therefore, we can rule out option
(D) sp3.
The question still refers to carbon
atoms, which we know to have electrons only in s orbitals and p orbitals. Option (A) and option (C) both have
d orbitals as part of the hybridization. Since carbon atoms don’t have any
electrons in d orbitals, we can also rule out option (A) and option (C).
Considering the shape and the
properties of graphene should help us figure out the hybridization that occurs in
the carbon atoms. Graphene has a similar structure to
that of this macromolecule. It is one layer thick, but the
structure extends further than the molecule does. Graphene is entirely composed of
carbon atoms, but each carbon atom only bonds to three other carbon atoms, whereas
in molecules such as methane, carbon forms four bonds. So, in graphene, only three of the
four valence electrons are involved in hybridization.
For the hybridization of carbon
atoms in graphene, the electrons start in the same orbitals as in the hybridization
of carbon atoms in molecules such as methane. An electron from the 2s orbital is
promoted to a 2p orbital, just as in sp3 hybridization. But instead of all four electrons
being involved in hybridization, only three of them are. The electron in the 2pz orbital
remains in the 2pz orbital. The hybrid orbitals are formed from
the electrons in 1s orbital and 2p orbitals. Thus, it is known as sp2
hybridization. So the carbon atoms in graphene
bond to each other via these sp2-hybridized orbitals.
The pz orbitals are not involved in
bonding, but the interaction between them allows electrons to move. It is the movement of electrons
from the pz orbitals that gives graphene its conductive properties. So we now know that the carbon
atoms in graphene are sp2 hybridized. Thus, option (B) sp2 is the correct
answer.
The type of hybridization mentioned
in option (E) sp occurs for molecules such as ethyne or acetylene, where the carbon
atoms bond to only two other atoms. sp hybridization is not the type of
hybridization that occurs in the carbon atoms of graphene. So the answer to the question
“Which type of hybridization is occurring in the carbon atoms of graphene?” is (B)
sp2.
