In excited state carbon atom gets its
one of the ‘2s’ electrons to say 2pz.
Each carbon atom has four unpaired
electrons when excited and tends to form
four covalent bonds.
• Where this energy to excite electron
comes from?
Linus Pauling - The world’s
one of the greatest scientists
and a great humanist. He was
acknowledged as the most
influential chemist.
He is the only person ever
to receive two unshared Nobel
Prizes — for Chemistry
(1954) and for Peace (1962).
We have to understand that free
carbon atom would not be in excited state
under normal conditions. When the
carbon atom is ready to form bonds with
other atoms, the energy required for
excitation is taken up from bond
energies, which are the liberated energies
when bonds are formed between carbon
atom and other atoms.
• In methane (CH4
) molecule all four
carbon – hydrogen bonds are
identical and bond angle HC^
H is
109°
28/. How can we explain this?
In the above discussion, we have
found that in excited state, carbon atom
has three unpaired electrons in p-orbitals
and one electron in s-orbital. These four
valence electrons are with different
energies.
• How these energetically unequal valence electrons form four equivalent
covalent bonds in methane molecule?
Let us see how?
Promotion of an electron
When bonds are formed, energy is released and the system becomes
more stable. If carbon forms four bonds rather than two, still more energy
is released and so the resulting molecule becomes even more stable.
