Bonding – Topic 4/14
Past Exam Questions from Questionbank (2nd set) - Markscheme
(a)
hybridization: mixing/merging of atomic orbitals;
N2 sp;
N2H2 sp2;
N2H4 sp3;
(b)
4
 bonds (result from the) overlapping of orbitals end to end/along inter-nuclear
axis;
 bonds (result from the) overlapping of parallel/sideways p orbitals;
(single bonds)  bonds only;
(double bonds) have a σ bond and a  bond;
Suitable clear and labelled diagrams acceptable for all
marks.
4
[8]
(i)
electron removed from higher energy level/further from nucleus/greater
atomic radius;
increased repulsion by extra inner shell electrons/increased shielding
effect;
(ii)
2
Mg2+(g)  Mg3+(g) + e;
(even though) valence electrons in the same shell/main energy level/
Mg2+ has noble gas configuration;
Mg has greater nuclear/core charge/more protons;
3
[5]
delocalized electrons;
(attracted) to positive ions;
more delocalized/mobile/outer shell electrons/higher ionic charge;
3
[3]
(a)
mixing/joining together/combining/merging of atomic orbitals to
form molecular orbitals/new orbitals/orbitals of equal energy;
Accept specific example such as mixing of s and p orbitals.
(b)
sp;
Do not award mark if sp2 or sp3 is also stated.
1
one sigma and two pi (bonds);
(c)
2
( bond formed by) end-on/axial overlap;
electrons/electron density between the two (carbon) atoms/OWTTE;
(π bond formed by) sideways/parallel overlap;
electrons/electron density above and below  bond/OWTTE;
Marks can be scored from a suitable diagram.
4
Do not award 2nd and 4th marks if electrons are not
mentioned.
[7]
Cl
N
Cl
Cl
All electrons must be shown.
Accept molecular structures using lines to represent bonding
and lone electron pairs.
bond angle: 107109
greater repulsion between lone pair and bonding pairs/OWTTE;
NOT between electron pairs and atoms.
Award [1 max] if lone pair missed on nitrogen, ECF for
bond angle of 120.
3
[3]
(i)
Cl
Cl
x
x
Cl
x
P
x
x
Cl
;
Cl
trigonal bipyramidal;
90;
120;
180;
Award [1] for 2 correct bond angles.
(ii)
3
xx
Cl x S
S xx
;
x
Cl
Bent/angular/V-shaped;
100107;
3
(iii)
Cl
Cl
;
I
Cl
Cl
square planar;
90;
3
No ECF allowed.
Penalize once only [1] mark for missing lone pairs.
Accept structures using lines to represent bonding and lone electron pairs.
[9]
(a)
(i)
mixing/combining of atomic orbitals/OWTTE;
(ii)
1
C60 fullerene: sp2;
graphite : sp2;
(iii)
(b)
(i)
diamond: sp3;
3
each carbon atom is bound to 3 other carbon atoms/ bonding;
leading to delocalized electrons;
2
sigma/ bonds are formed by orbitals overlapping end to end/
along the internuclear axis/along line directly between nuclei;
Accept suitable diagram.
pi/ bonds are formed by p orbitals overlapping sideways;
Accept suitable diagram.
(ii)
12 sigma bonds;
2 pi bonds;
2
2
[10]
NH4+ > NH3 > NH2–;
NH4+ has four bonded electron pairs (and no lone electron pairs);
NH3 has three bonded electron pairs and one electron lone pair;
NH2– has two bonded electron pairs and two electron lone pairs;
Accept correct Lewis structures with lone electron pairs
clearly shown.
lone pair-lone pair > lone pair-bonded pair > bonded pair-bonded pair/
lone pairs of electrons repel more than bonding pairs of electrons/OWTTE;
Do not accept repulsion between atoms.
5
[5]
(i)
Find number of electron pairs/charge centres in (valence shell of)
central atom;
electron pairs/charge centres (in valence shell) of central atom repel
each other;
Any one of the following:
to positions of minimum energy/repulsion/maximum stability;
pairs forming a double or triple bond act as a single bond;
non-bonding pairs repel more than bonding pairs/OWTTE;
Do not accept repulsion between bonds or atoms.
3 max
(ii)
6
Species
H3O+
C2H4
(iii)
Lewis (electron-dot)
structure
+
–
O
H ;
H H
H
Shape
Bond angle(s)
Trigonal/triangular
pyramidal;
Allow values in the
range 106° to 109.5°;
H
Trigonal/triangular
Allow values of
;
planar;
approximately 120°;
H
H
Accept crosses and dots for electrons in Lewis structures
also.
As the Lewis structures were asked for, and not 3D
representations, do not penalize incorrectly drawn
geometries.
Do not accept structure of hydronium cation without lone
pair on oxygen.
No penalty for missing charge.
H3O+: is polar and explanation either using a diagram or in words,
involving the net dipole moment;
e.g. the three individual O-H bond dipole moments add as
vectors to give a net dipole moment.
C2H4: is non-polar and explanation either using a diagram or in words,
involving no net dipole moment;
e.g. the vector sum of the individual bond dipole moments is
zero.
For simple answers such as bond polarities do not cancel for
H3O+ and do cancel for C2H4, Award [1], only for the last
two marking points.
2
(iv)
O-H is most polar;
O-H has greatest difference between electronegativities/calculation
showing values of 1.4, 0.5 and 0.9 respectively;
2
[13]
(i)
3
Allotrope
(ii)
Structure
Diamond
3D array/network involving tetrahedral
carbons/each carbon atom joined to four others;
Graphite
layer structure involving trigonal (triangular) planar
carbons/with each carbon atom joined to three
others/with hexagonal (six-membered) rings of
carbon atoms;
C60 fullerene
truncated icosahedrons;
Accept carbon atoms form a ‘ball’ with 32 faces, of
which 12 are pentagons and 20 are hexagons,
exactly like a soccer ball. Do not accept soccer ball
alone.
Diamond: covalent bonds (only);
Graphite: covalent bonds and the separated layers held together by
(weak) London/van der Waals’/dispersion forces;
2
[5]
Electrical conductivity:
Bonding electrons are delocalised;
Current flow occurs without displacement of atoms within the metal/
able to flow within the metal;
Malleability:
Can be hammered into thin sheets;
atoms capable of slipping with respect to one another;
4
[4]
(a)
mole ratio C:H =
85.6 : 14.4
= 7.13:4.3;
12.01 1.01
No penalty for using integer atomic masses.
empirical formula is CH 2 ;
(b)
(i)
2
1.01  10 2 kPa (0.399 dm 3 );
PV
mass

;
number of moles of gas n =
;
RT molar mass
8.314 J (273 K)
mol K
1.00 g
= 56.3 (g mol–1)
0.017 mol
2
OR
molar mass is the mass of the molar3 volu me at STP;
22.4 dm
1.00  22.4 = 56.1 (g mol–1)
=
0.399
Accept answers in range 56.0 to 56.3.
Accept two, three or four significant figures.
(ii)
C4H8;
1
No ECF.
[5]
(a)
atoms of the same element/same number of protons/same atomic number;
having different numbers of neutrons/different (mass number);
Award only [1] max if reference made to elements but
not atoms.
(b)
relative atomic mass =
(c)
23 electrons;
26 protons;
30 neutrons;
36  0.337  38  0.0630  40  99.6
;
100
2
2
2
Award [2] for three correct, [1] for two correct.
[6]