CHEMISTRY 7405 PAPER 3 COMPREHENSIVE
ASSESSMENT 2026 SOLVED QUESTIONS
VERIFIED
◉ Solid Lattices. Answer: -Giant Metallic lattices
-Giant ionic lattices
-Giant covalent lattices
-Discrete (simple) molecular lattices
◉ Giant covalent lattices. Answer: Consist of a large network of
atoms held together by covalent bonds. The 4 most common ones
are:
-Diamond
-Graphite
-Graphene
-Silicon (IV) oxide
◉ Diamond structure. Answer: Every carbon atom has 4 covalent
bonds connecting it to another 4 carbon atoms.
◉ Graphite. Answer: In graphite each carbon atom has only 3
covalent bonds with another carbon and thus forms layers.
,The layers are close enough that the p orbitals overlap and produce
a cloud of delocalised electrons, therefore it can conduct electricity
but only parallel to it's layers.
Graphite can also be used as a lubricant as the layers can easily slide
over each other. This is due to absorbed gases on the surface of the
carbon atoms though.
◉ Graphene. Answer: Pure carbon in the form of a very thin sheet,
one atom thick.
It is very strong (200 x stronger than steel)
◉ Molecular lattices. Answer: The two most common forms of this is
ice and iodine. In solid iodine, the diatomic I₂ molecules are
arranged in a regular pattern, giving it it's crystaline nature.
◉ Creating half equations. Answer: We can create reduction or
oxidation half equations by:
-Firstly balancing all elements except for O and H
-Balance all oxygen with H2O
-Balance all hydrogen with H+
-Add electrons to balance half equations
You can then balance and add half equations to create a full equation
,◉ Oxidation number rules. Answer: -Oxidation number of a lone
element is 0
-Sum of oxidation numbers in a neutral compound is 0
-Sum of oxidation numbers in ions = total charge
-More electronegative elements have a negative oxidation number
-Oxidation number of fluorine is always 1
-Oxidation number of H is +1 except when it is bonded with a less
electronegative element, then it is -1
-Oxidation number of Oxygen is 2- except in peroxide (-1) and when
combined with fluorine (+1)
◉ Systematic names. Answer: oxidation numbers can be written in
brackets in roman numerals after an element in a compound. This
can be used to work backwards and find out the molecular formula
of the compound.
◉ Oxidation. Answer: the loss of electrons
◉ Reduction. Answer: the gain of electrons
◉ oxidising agent. Answer: a species that oxidises another species
, ◉ Reducing agent. Answer: An species that reduces another species
◉ Oxidation number. Answer: the charge that an ion or a species
would have if it were fully ionic.
◉ Disproportiation reaction. Answer: a reaction where oxidation
and reduction occurs in the same species at the same time.
◉ Ionisation energy trend in Group 2. Answer: As you go down the
group first ionisation energy decreases because:
- Although nuclear charge is increasing
- The electrons have an extra quantum shell of shielding making
them easier to remove
- They exist in a higher energy orbital (and/ or a further distance
from the nucleus)
◉ Reactivity trend in group 2. Answer: Group 2 elements become
more reactive going down a group as the outer two electrons are
easier to remove because they have lower first ionisation energies.
◉ Group 2 reactions with oxygen. Answer: 2M(s) + O₂(g) -> 2MO(s)
This reaction occurs vigorously when heated, but even when not
heated occurs very slowly
ASSESSMENT 2026 SOLVED QUESTIONS
VERIFIED
◉ Solid Lattices. Answer: -Giant Metallic lattices
-Giant ionic lattices
-Giant covalent lattices
-Discrete (simple) molecular lattices
◉ Giant covalent lattices. Answer: Consist of a large network of
atoms held together by covalent bonds. The 4 most common ones
are:
-Diamond
-Graphite
-Graphene
-Silicon (IV) oxide
◉ Diamond structure. Answer: Every carbon atom has 4 covalent
bonds connecting it to another 4 carbon atoms.
◉ Graphite. Answer: In graphite each carbon atom has only 3
covalent bonds with another carbon and thus forms layers.
,The layers are close enough that the p orbitals overlap and produce
a cloud of delocalised electrons, therefore it can conduct electricity
but only parallel to it's layers.
Graphite can also be used as a lubricant as the layers can easily slide
over each other. This is due to absorbed gases on the surface of the
carbon atoms though.
◉ Graphene. Answer: Pure carbon in the form of a very thin sheet,
one atom thick.
It is very strong (200 x stronger than steel)
◉ Molecular lattices. Answer: The two most common forms of this is
ice and iodine. In solid iodine, the diatomic I₂ molecules are
arranged in a regular pattern, giving it it's crystaline nature.
◉ Creating half equations. Answer: We can create reduction or
oxidation half equations by:
-Firstly balancing all elements except for O and H
-Balance all oxygen with H2O
-Balance all hydrogen with H+
-Add electrons to balance half equations
You can then balance and add half equations to create a full equation
,◉ Oxidation number rules. Answer: -Oxidation number of a lone
element is 0
-Sum of oxidation numbers in a neutral compound is 0
-Sum of oxidation numbers in ions = total charge
-More electronegative elements have a negative oxidation number
-Oxidation number of fluorine is always 1
-Oxidation number of H is +1 except when it is bonded with a less
electronegative element, then it is -1
-Oxidation number of Oxygen is 2- except in peroxide (-1) and when
combined with fluorine (+1)
◉ Systematic names. Answer: oxidation numbers can be written in
brackets in roman numerals after an element in a compound. This
can be used to work backwards and find out the molecular formula
of the compound.
◉ Oxidation. Answer: the loss of electrons
◉ Reduction. Answer: the gain of electrons
◉ oxidising agent. Answer: a species that oxidises another species
, ◉ Reducing agent. Answer: An species that reduces another species
◉ Oxidation number. Answer: the charge that an ion or a species
would have if it were fully ionic.
◉ Disproportiation reaction. Answer: a reaction where oxidation
and reduction occurs in the same species at the same time.
◉ Ionisation energy trend in Group 2. Answer: As you go down the
group first ionisation energy decreases because:
- Although nuclear charge is increasing
- The electrons have an extra quantum shell of shielding making
them easier to remove
- They exist in a higher energy orbital (and/ or a further distance
from the nucleus)
◉ Reactivity trend in group 2. Answer: Group 2 elements become
more reactive going down a group as the outer two electrons are
easier to remove because they have lower first ionisation energies.
◉ Group 2 reactions with oxygen. Answer: 2M(s) + O₂(g) -> 2MO(s)
This reaction occurs vigorously when heated, but even when not
heated occurs very slowly
