Engineering Chemistry S Datta

22 ENGINEERING CHEMISTRY
In boron trifluoride the sp 2 hybrid orbitals of B atom overlap with p orbitals of three F
atoms along the axes to form three sigma bonds (Fig. 2.11). Boron atom has electronic
configuration, 1s 2 2s 2 2p 1 . 2s and 2p hybridise electrons to produce three sp 2 hybrid orbitals
directed towards the vertices of an equilateral triangle.
F
2
sp –p ( –bond)
B
2
sp –p ( -bond)
F
2
sp –p ( -bond)
F
Fig. 2.11 Formation of triangular planar BF 3
molecule. (Another example of sp 2 hybridization).
sp-hybridization
Electronic configuration of:
C in the ground state
C in the excited state
1s 2s 2p
p x p y
p z
Four unpaired
electrons
Electronic configuration
of sp hybridized C-atom
sp hybridization
In the structure of acetylene sp-hybridization takes place. In the excited state of C-atom
there are two hybrid orbitals (sp) and two unchanged p-orbitals. During combination with
H-atom, two sp-hybrid orbitals overlap along the axis to give a σ-bond. Then two C-atoms
possess total four unchanged p-orbitals. They overlap laterally to give two π-bonds. So triple
bond of acelylene molecule contains one σ-bond and two π-bonds.
H
H HC CH
Fig. 2.12 Structure of acetylene.
In BeF 2
molecule the central atom Be has electronic configuration ⇒ 1s 2 . 2s 2 in its
ground state. Since, there is no unpaired electron, the Be atom cannot form any covalent bond.
2p