Lets discuss about hybridization. The simple example is methane, CH4 molecule. Carbon, C-6 (2,4) has four valence electrons. To achieve an octet, C atom needs four electrons and each hydrogen atom needs an electron to achieve a
duplet. Each electron from C atom and H atom share one of another, to form polar covalent bond. There are four single covalent bond in CH4 molecule. Although the bonding is polar, the molecule is non polar, because according to the theory of Valence Shell Electron Pair Repulsion (
VSEPR), the repulsion between C - H bond is the same.
Okay, when we look at the experimental data, it showed that carbon formed four identical C - H covalent bonds in methane. Its molecular geometry is tetrahedral. From this evident, the carbon atom acts as though it has four unpaired electrons. Linus Pauling invented a hybridization concept. This concept is about the rearrangement of electrons within the valence orbitals of C atom.
To come to the hybridization concept, look at the orbital diagram of carbon atom in the ground state condition.
C-6 : (1s2 2s2 2p2). According to the Hund Rule, the position of two electrons in the p orbitals, are separated into px and py orbitals with the same spin quantum number, i.e. +1/2.
When carbon atom combines with hydrogen atom, the simple molecule that can be formed is methane, CH4. Each C atom bonds with 4 H atoms. This is an unusual bond, because C atom only has two single electrons, so it must be 2 H atoms are bonded with each C atom. However, if C atom only bonds with 2 H atoms, the outer shell of C atom only contains 6 electrons. The rule for achieving stability of electrons are
duplet (2 electrons filled) or octet (8 electrons filled). T
his evident that there is a special bond and an unusual bond, is called HYBRIDIZATION which has been mentioned above.
An rearrangement of electrons is occurred from the ground state, 1s2 2s2 2px1 2py1 2pz0 becomes 1s2 2s1 2px1 2py1 2pz1. One electron from 2s1 moves to 2pz1, so after the electron promotes, C atom has 4 unpairs electrons in the four orbitals. This condition, we called in the excited state. Immediately, almost at the same time, there is an energy transfer from the electrons in the 2p orbitals to the electron in 2s orbital. The four orbitals 2s,. 2px, 2py, and 2pz have the same energy level. This evident is called a hybridization. Because there are one s orbital and three p orbitals change, each orbital named as sp3 orbital. Now, there are 4 hybrid orbitals, e.i. sp3 hybrid orbitals.
Be careful, the hybridization concept is a hypothetical concept, so don't use hybridization to predict the shape of molecules or ions. The geometry should be known first, and you can predict its hybridization.
Hybridization can be sp, sp2, sp3, dsp2, etc. Apply this concept to other examples, then you can learn other type of hybridization.
Look at this diagram. Now think about hybridized sp2 orbitals. The above electron configuration is in the excited state, because one of electrons in the 2s orbital has promoted to the 2py orbital.
