Q4. Give the hybridisation of each carbon in CH3–C≡C–CHO (but-2-ynal), from left to right.
CH3: four σ bonds, sp3. The two C≡C carbons: two σ bonds each, sp. The CHO carbon (C=O): three σ bonds, sp2. So sp3, sp, sp, sp2.
Q5. How many σ and π bonds are there in benzene, C6H6, drawn with three alternating double bonds?
Ring C–C σ: 6; C–H σ: 6; so 12 σ. π: 3 (one in each C=C).
Q6. Arrange sp, sp2 and sp3 carbon in order of increasing electronegativity, and explain.
sp3 < sp2 < sp. The s character rises from 25% to 33% to 50%; s electrons are held closer to the nucleus, so a carbon using orbitals with more s character attracts bonding electrons more strongly.
Q7. Describe the bonding and shape of hydrogen cyanide, HC≡N.
Carbon is sp hybridised: one σ bond to H and one σ bond plus two π bonds to N. The molecule is linear (180°), with 2 σ and 2 π bonds in all.
Q8. Which of ethane, ethene and allene (CH2=C=CH2) has all its atoms in one plane? Explain.
Only ethene. Ethane is built from two tetrahedral sp3 carbons, so its hydrogens cannot all lie in one plane. In allene, the two π bonds at the central sp carbon use p orbitals at right angles to each other, so the two CH2 groups lie in perpendicular planes.