NCEA Level 1 Chemistry (90172) 2010 — page 1 of 3
Assessment Schedule – 2010
Chemistry: Describe atomic structure and bonding (90172)
Evidence Statement
Q
Evidence
ONE
(a)
Achievement
Achievement with
Merit
Achievement with
Excellence
BOTH formulae
correct.
ONE formula
correct.
BOTH formulae
correct.
OR
Describes NaCl as
having an ionic bond /
ionic compound with
electrostatic forces /
transfer of electrons.
AND
A diagram /
explanation
showing the
formation of ionic
bond.
AND
A diagram /
explanation
showing the
formation of ionic
bond.
OR
Identifies SCl2 having
covalent bonds.
OR
Lewis Structure of
SCl2 / explanation
of covalent bond.
AND
Lewis Structure of
SCl2 / explanation
of covalent bond.
OR
Recognises that the
forces are much
stronger in NaCl than
SCl2 (weak covalent
negates).
AND
Explains that NaCl
is made up of ions
held together by
strong ionic
bonds.
AND
Explains that NaCl
is made up of ions
held together by
strong ionic
bonds.
OR
Correctly names the
particles in NaCl and
SCl2.
OR
SCl2 is made up of
molecules of
strong covalent
bonds.
AND
SCl2 is made up of
molecules (of
strong covalent
bonds) held
together by weak
intermolecular
forces.
THREE of:
NaCl
SCl2
(b)
The bond between Na and Cl involves a
transfer of Na’s outer valence electron to
Cl’s valence shell to form an ionic bond.
Candidates may choose to use diagrams in
answer.
(
) These non-metal elements
share valence electrons in order to get full
octets. This is a covalent bond.
(c)
Sodium chloride is an ionic compound. In
solid ionic compounds, ions are held
together by strong ionic bonds /
electrostatic forces between ions.
To melt sodium chloride, these very strong
ionic bonds need to be broken. This requires
a lot of energy / bonds are harder to break, so
sodium chloride will have a high melting
point.
Sulfur dichloride is a (covalent) molecule
with weak intermolecular forces between
the molecules.
(It is made up of non-metal atoms, so it will
have covalent bonds.)
To melt sulfur dichloride, the weak
intermolecular forces need to be broken. This
requires little energy / bonds are easier to
break, so sulfur dichloride will have a lower
melting point than sodium chloride.
OR
SCl2 is made up of
molecules held
together by weak
intermolecular
forces.
AND
Links melting point
to the type of
attractive forces in
ONE compound.
Must relate to
amount of energy
required.
AND
Links melting
point to the type of
attractive forces in
ONE compound.
Must relate to
amount of energy
required.
NCEA Level 1 Chemistry (90172) 2010 — page 2 of 3
TWO
(a)
(b)
Any TWO correct
Any TWO correct
Any THREE
correct
(All diagrams must
follow convention with
electrons shown as
either dots or crosses
and clearly paired as
appropriate).
(All diagrams must
follow convention
with electrons
shown as either
dots or crosses and
clearly paired as
appropriate).
(All diagrams must
follow convention
with electrons
shown as either
dots or crosses and
clearly paired as
appropriate).
AND
AND
K2O is an ionic solid / network / lattice held
together by strong ionic bonds between the
ions.
K2O is ionic AND has
charged particles / ions
(NB: electrons negate).
TWO of the
following three
ideas linked:
In the solid state in K2O, these ions are fixed
in place and not free to move. But in the
liquid state, the ions become mobile as ionic
bonds are broken and the ions can carry a
charge.
OR
CO2 covalent /
molecular AND has no
charge.
 liquid K2O has
mobile ions.
CO2 is a covalent molecule.
OR
K2O is ionic and CO2
is covalent / molecular.
In both the solid and liquid state, there are no
ions or free electrons to carry the charge,
only molecules / molecules are not charged
particles so cannot carry an electric current.
THREE
 solid K2O has no
mobile ions.
K2O and CO2 are
fully discussed
with respect to
ionic bonding in
K2O and particles
present for both,
and their states are
accurately linked
to electrical
conductivity.
 as a molecule,
CO2 has no
mobile charged
particles in either
state.
PCl3 is a (covalently bonded) molecule.
The attractive forces between the molecules
are (weak) intermolecular forces.
Correctly identifies
PCl3 particles as
molecules
Correctly identifies
PCl3 particles as
molecules
Correctly identifies
PCl3 particles as
molecules
A refers to the first part of the cooling curve,
where the PCl3 is liquid and the temperature
is decreasing. Over this time, the molecules
are:

Separation: moving closer together

Energy: losing energy

Motion: slowing down

Attractive forces: weak intermolecular
bonds present (becoming stronger)
AND
that there are
intermolecular forces
between the molecules.
AND
that there are
intermolecular
forces between the
molecules.
AND
that there are
intermolecular
forces between the
molecules.
OR
Interprets graph
correctly by describing
TWO of the four
points for Part A AND
Part B.
AND
Interprets graph
correctly by:
AND
Interprets graph
correctly by
explaining what is
happening for each
of the points for
Part A AND Part
B.
B refers to the second part of the cooling
curve, where the liquid PCl3 is solidifying.
During this time, the molecules are:

Separation: packed closely together

Energy and Attractive forces: forming
(stronger) intermolecular bonds as
energy is released, so no change in
temperature (counts as TWO points)

Motion: only vibrating
Answers must relate to CHANGES
occurring during Part A, not simply a
description of a liquid for Part A.
EITHER
Explaining what is
happening in Part
A AND one point
from Part B.
OR
Explaining what is
happening in Part B
AND one point
from Part A.
OR
Explaining 3 of 4
points for Part A
AND Part B.
AND
Although cooling
is still occurring,
the temperature is
constant because
energy is released
as intermolecular
bonds are forming.
NCEA Level 1 Chemistry (90172) 2010 — page 3 of 3
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E+1A