AS-Level Chemistry Chapter 4 Chemical Bonding Hybridization
Hybridization
1) Hybridization is the mixing of atomic orbitals to produce a new set of hybrid orbitals of equivalent energies. This is a theory used to account for the discrepancies in explaining the shapes of covalent molecules.
2) There is a problem with simple view on methane, CH4. Methane has two unpaired electrons only in its outer shell to share with the hydrogen atoms, but the formula of methane is not CH2.
3) The concept of hybridization is used to account for this discrepancy.
4) General steps in hybridization:
ii. mixing of orbitals to produce a new set of hybrid orbitals of equivalent energies(sp, sp² or sp³ hybrid orbitals)
iii. forming of a new molecular orbital.
sp³ hybridization
1) An example of compound which undergoes sp³ hybridization is methane, CH4.
2) The carbon atom uses some energy to promote one of its electron from 2s to empty 2p orbital so that there are four unpaired electrons for covalent bonding.
3) The carbon now is said to be in an excited state(C*).
4) The orbitals then 'mix' or hybridize to produce four hybrid orbitals of equivalent energies. The new orbitals are called sp³ hybrid orbitals because they are made from one s orbital and three p orbitals.
5) Each hybrid orbital has one big lobe and one small lobe. They rearrange themselves so that they are as far as possible to form a tetrahedral geometry. The hybrid orbitals are 109.5° apart.
6) The s orbitals from the hydrogen atoms then overlap with the four hybrid orbitals to form four sigma bonds because the overlapping is end-to-end. All the bonds are identical.
7) Another example is ethane, C2H6. The two carbon atoms undergo sp³ hybridization to form four hybrid orbitals. The two carbon atoms are bonded by overlapping one of their hybrid orbitals. The remaining ones then overlap with the s orbitals of the hydrogen atoms.
8) The bond angle is approximately 109.5°. This is an approximation because all the bonds are not identical.
sp² hybridisation
1) An example of compound which undergoes sp² hybridization is ethene, C2H4.
2) The same thing happens as in sp³ hybridization, except that this time the carbon atoms 'mix' or hybridize three of the four orbitals only because the carbon atom is bonding with three other atoms only.
3) This produces three sp² hybrid orbitals because they are made from one s orbital and two p orbitals. Another p orbital remains unchanged and it is perpendicular to the plane containing the hybrid orbitals.
4) The hybrid orbitals rearrange themselves so that they are as far as possible, that is, a trigonal planar arrangement, the hybrid orbitals are 120° apart.
5) The hybrid orbitals then overlap with s orbitals from the hydrogen atoms and another hybrid orbital from the other carbon atom to form five sigma bonds. The remaining p orbitals overlap sideways to form a pi bond. A double bond is formed between the two carbon atoms.
6) Another example is boron trichloride, BCl3. The boron atom undergoes sp² hybridization to produce three sp² hybrid orbitals. The hybrid orbitals rearrange themselves to form a trigonal planar geometry. The p orbitals from chlorine atoms then overlap with the hybrid orbitals to form three sigma bonds.
sp hybridisation
1) An example of compound which undergoes sp hybridization is ethyne, C2H2.
2) The same thing happens as in sp³ and sp² hybridization, except that this time the carbon atoms 'mix' or hybridize two of the four orbitals only because the carbon atom is bonding with two other atoms only.
3) This produces two sp hybrid orbitals because they are made from one s orbital and one p orbital. The other two p orbitals remain unchanged and they are perpendicular to each other and to the two hybrid orbitals.
4) The hybrid orbitals rearrange themselves so that they are as far as possible, that is, a linear arrangement, the hybrid orbitals are 180° apart.
5) The hybrid orbitals overlap with the s orbitals from the hydrogen atoms and to the hybrid orbital from the other carbon atom to form three sigma bonds. The remaining p orbitals overlap sideways to form two pi bonds. A triple bond is formed between the two carbon atoms.
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