1.	B
[1]

2.	A
[1]

3.	delocalization/spread of pi/π electrons over more than two nuclei;
equal bond order/strength/length / spreading charge (equally) over all
three oxygens;
gives carbonate ion a greater stability/lower potential energy;	3
M3 can be scored independently.
Accept suitable labelled diagrams for M1 and M2 e.g.
	
	OR
	
	Do not penalize missing brackets on resonance structure but 2– charge must
be shown.
Allow –2 for charge on resonance structure.
[3]

4.	mixing/combining/merging of (atomic) orbitals to form new orbitals (for bonding);
Allow molecular or hybrid instead of new.
Do not allow answers such as changing shape/symmetries of atomic orbitals.
	Carbon dioxide: sp;
Diamond: sp^3;
Graphite: sp^2;
Carbonate ion: sp^2;	5
[5]

5.	C
[1]

6.	D
[1]

7.	A
[1]

8.	B
[1]

9.	C
[1]

10.	D
[1]

11.	D
[1]

12.	A
[1]

13.	A
[1]

14.	(a)	(i)	(bond formed by) sideways overlap;
(of) p orbitals;
Marks awarded either from sketch or from explanation.	2
 
(ii)	C(l) is sp^3 and C(2) is sp^2;	1

(b)

cis but-2-ene/Z-but-2-ene;	2
 
(c)
	1
[6]

15.	(i)	acid-base/neutralization;	1
 
(ii)	109° /109.5°;	1
 
(iii)	sp^3;
No ECF if bond angle incorrect in (ii).	1
[3]

16.	A
[1]

17.	A
[1]

18.	(i)

trigonal pyramid;
in the range of 100–108°;	3

(ii)

Must include minus sign for the mark.
bent/V–shaped;
in the range of 100–106°;	3
 
(iii)

square planar;
90°;
Penalize once only if electron pairs are missed off outer atoms.	3
[9]

19.	A
[1]

20.	A
[1]

21.	A
[1]

22.	(i)

	octahedral/octahedron/square bipyramidal;
90° / 90° and 180°;	3

(ii)

	linear;
180°;
	Allow dots, crosses or lines in Lewis structures.
Penalize missing charge, missing bracket once only in (i) and (ii).
Lone pairs required for BOTH (i) and (ii).	3
[6]

23.	A
[1]

24.	
| SF_2 | SF_4 | SF_6

Lewis
structure

2 lone pairs on S required for the mark

1 lone pair on S required for the mark

Name of
shape

bent/angular/V shaped;

Seesaw/distorted tetrahedral;

octahedral;
Accept square bipyrimidal

	Penalize missing lone pairs on fluorine atoms once in correct structures only.
For Lewis structures candidates are not expected to draw exact shapes of molecules.
Do not allow ECF for wrong Lewis structures.
Accept dots or crosses instead of lines.	6
[6]

25.	C
[1]

26.	D
[1]

27.	(i)

Species

Lewis (electron-dot)
structure

Shape

Bond angle(s)

NO_2^– | | Bent/V- shaped/angular; | 109.5° < θ < 120°;
ICl_5 | | Square pyramidal; | |Inplane Cl-I-out-of-plane Cl| < 90°; Allow corresponding correct statement for other correctly identified bond angles.
SF_4 | | See-saw; | |Equatorial F-S-Equatorial F| < 120°; Allow corresponding correct statement for axial-equatorial and axial-axial F-S-F angles.
		9
Accept crosses and dots for electrons in the Lewis structures also.
If all ideal bond angles are given, penalize once only.
As the Lewis structures were asked for, and not 3D representations, do not penalize incorrectly drawn geometries.
 
(ii)	(equatorial F-S-equatorial F) less than 120° since non-bonding electron pairs
(exert greater repulsive forces and thus) compress the bond angles / OWTTE;	1
 
(iii)	orbital diagram representation of carbon ground-state going to carbon
excited-state electron configuration;
mixing of orbitals to give three new entirely equivalent hybrid orbitals, sp^2,
on each carbon;
sp^2 orbitals trigonal (triangular) planar in shape;
unhybridized orbitals overlap to give π-bond;	4
 
(iv)	sp^2;
both N-O bond lengths equal, (intermediate between double and single
bonds) due to resonance/delocalization;	2
 
(v)	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
[18]

IB Questionbank Chemistry