Chemical Bonding and Hybrid Orbitals

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					                Chemical Bonding and Hybrid Orbitals

     Chemical bonds can be considered the overlap of adjacent
orbitals. In the case of H-Cl, the 1s orbital of H can overlap with
the 3pz orbital of Cl and form a (polar) covalent bond.

           1s                                      2p

This overlap will fill both vacant orbitals of the two atoms and is
called a (sigma) s- bond.

      In the case of CH4, we would expect it to have 3 C-H bonds
identical and 1 C-H bond of differing energy because they are
bonding with a different atomic orbital (C has 1 2s orbital and 3
2p orbitals available for bonding in its first excited state).

In reality there are four identical bonds. This leads to the
bonding theory that the s and p orbitals combine and make four
identical hybrid orbitals called sp3.

      This bonding theory can also account for multiple bonds. In
the case of formaldehyde, H       , the central atom (AX3) has the
                                C == O::
bonding orbital sp . This accounts for the overlaps between the
atoms but not the double bond. The bonding theory states that
the extra 2pz filled orbital of carbon will have a sideways overlap
with the adjacent orbital of oxygen. This is called a (pi) Π- bond.

The formaldehyde structure has 3s and 1Π bond.