Complete the diagrams to show the energies of the electrons in a carbon atom, a C+ ion and a C– ion.

Question 1 [Chemical Bonding > Hybridisation and covalent bonding]

(a) Complete the diagrams to show the energies of the electrons in a carbon atom, a C+ ion and a C– ion.

 

Reference: Past Exam Paper – Chemistry (9701) March 2016 Paper 42 Q1

Solution:

a)     C (6 electrons): 1s² 2s² 2p² [2/3 subshells  filled with 1 electron each]

        C+ (5 electrons): 1s² 2s² 2p¹  [1/3 subshells filled with 1 electron each]

        C- (7 electrons): 1s² 2s² 2p³ [all 3 subshells filled with one unpaired electron each]

b)

(i)Since 3 bonds are seen to originate from each carbon atom, hybridisation is sp² (1+2=3)

(number of bonds due to a type of hybridisation is equal to sum of powers of s and p orbitals; eg: sp³ (1+3=4) therefore 4 bonds; tetrahedral shape. You can also work backwards, CH₄ = four bonds= 1+3= sp³ hybridisation)

(ii) in an sp² hybridisation, we have one unhybridised p orbital. Upon reaction with excess hydrogen, this p orbital takes part in bonding with the H atom. Per carbon, 1 unhybridised p orbital = 1 added H atom/ Carbon atom=> final formula= c₆₀H₆₀

c) [Substitution reactions in Arenes]

(i)

   1: Cl₂  and UV light (since substitution is made in side chain and not on benzene ring)

   2: AlCl₃ and Cl₂ (since substitution is made in benzene ring and not on side chain)

(ii) every time we use UV light, the answer is FREE RADICAL SUBSTITUTION.

(iii) Ideally, if carried out in excess, all hydrogen atoms on side chain are substituted to give benzene-CCl₃ {this is the most appropriate answer}

Solutions provided by Kashish Varshney, India