How many covalent bonds are present in a Chloropropane molecule having molecular formula, C3H7Cl ?
- (a)6
- (b)8
- (c)9
- (d)10
Correct — D, 10. Chloropropane (C3H7Cl) is propane with one hydrogen replaced by chlorine. Counting every single covalent bond: the three carbons form a chain with 2 C-C bonds, the seven hydrogens give 7 C-H bonds, and the chlorine gives 1 C-Cl bond. That is 2 + 7 + 1 = 10 covalent bonds in all.
- (a)6 — Far too few - this counts only some of the C-H bonds and misses the C-C skeleton bonds and the C-Cl bond; a C3H7Cl molecule has ten bonds in total.
- (b)8 — This counts the 7 C-H bonds and the 1 C-Cl bond but forgets the 2 C-C bonds of the carbon chain (8 instead of 10).
- (c)9 — This misses one bond - for example counting the 2 C-C and 7 C-H bonds but leaving out the single C-Cl bond (9 instead of 10).
A covalent bond is a shared pair of electrons, and 'how many bonds' means counting these shared pairs, each single bond as one. Chloropropane (C3H7Cl) is a haloalkane; carbon is tetravalent (four bonds each), while hydrogen and chlorine form one bond each.
Draw the structure CH3-CH2-CH2Cl (1-chloropropane): every line in the structural formula is one covalent bond. Add up the C-C, C-H and C-Cl bonds.
- A covalent bond is a shared pair of electrons; counting bonds means counting these shared pairs (each single bond counts as one).
- In C3H7Cl the chain has 2 C-C bonds, plus 7 C-H bonds and 1 C-Cl bond, totalling 10.
- Carbon is tetravalent - each of the three carbons uses exactly four bonds, while hydrogen and chlorine use one each.
- A quick check using valencies: (4x3 + 1x7 + 1x1) / 2 = 20 / 2 = 10 bonds, matching the direct count.
Add the skeleton (C-C), the C-H and the C-Cl bonds: 2 + 7 + 1 = 10 covalent bonds.
- Forgetting the C-C skeleton bonds and counting only C-H and C-Cl bonds.
- Miscounting the hydrogens - C3H7Cl has 7, not 8, hydrogens.
- Confusing the number of bonds with the number of atoms.
NDA gives a molecular formula and asks for the number of covalent bonds - draw the structure and count the C-C, C-H and C-X bonds.
No directly related past PYQ was found.
- practice — not a real PYQ
How many covalent bonds are present in a methane (CH4) molecule?
- (a)2
- (b)3
- (c)4
- (d)5
Answer(c) 4 - one carbon bonded to four hydrogens by four C-H bonds.
- practice — not a real PYQ
In a propane molecule (C3H8), the number of C-H bonds is
- (a)6
- (b)7
- (c)8
- (d)10
Answer(c) 8 - the eight hydrogens each form one C-H bond.