Page 49 - ACE YR IGCSE A TOP APPROACH TO CHEM

or 9 (a) (i) Neon [1]
Valency + valence electrons = 8 [1] Neon is a noble gas. It is monatomic at room
because this is the number of electrons needed temperature because it is unreactive.
to achieve a full outer shell. [1] (ii) Lithium / Beryllium [1]
(d) (i) Basic oxide to amphoteric oxide to acidic All Group I and II elements form a metal
oxide [2] hydroxide which is alkaline when react with
Metal oxide is basic. water.
Non-metal oxide is acidic. 2Li + 2H O ➞ 2LiOH + H 2
2
Aluminium oxide is amphoteric. (iii) Nitrogen [1]
(ii) Ionic bond [1] 78% of the air is nitrogen. 21% is oxygen.
to covalent bond [1] (iv) Oxygen [1]
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Metals form ionic compounds with chlorine. Iron reacts with oxygen to form iron(II) oxide. It
Chlorine forms covalent bonds with non-metals. is known as rusting.
(e) Macromolecule [1] (v) Lithium [1]
Tetrahedral [1] Lithium is a soft metal which is very reactive.
One silicon atom is bonded to four chlorine It must be stored in oil to stop lithium from
atoms. [1] reacting with oxygen in the air.
(f) (vi) Fluorine [1]
(vii) Carbon [1]
Carbon is inert. It does not react in the
H S H
electrolysis but conducts electricity.
(b) (i) BF [1]
3
(ii) BeF [1]
Correct ratio for H and S [1] 2
2 lone pairs and 2 bonded pairs [1] (iii) Li N [1]
3
8 (a) A and F [1] 10 (a) Any one from:
Both have a full outer shell. [1] (i) Fluorine
Element A has only 1 shell. 2 electrons in the outer Physical property: [1]
shell are considered full. • Yellow gas
• Low boiling point
(b) C and E [2] • Poor conductor of electricity / heat
An ionic compound is formed from the reaction
between a metal and a non-metal. To form a • Low density
compound with the formula of XY, the ratio of the • Soluble in water
charges carried must be 1 : 1. Element C has the Chemical property: [1]
valency of +1, and element E has the valency of –1. • Poisonous
The charges cancel out each other to form an ionic
compound that has zero overall charge. • Forms diatomic molecules
• Reacts with hydrogen to form HF
(c) D [1] • Valency / Oxidation state (–1)
Element D has the valency of –3. Fluorine has the • Forms F –
valency of –1. 1 D atom reacts with 3 fluorine atoms • Reacts with metals / named metal
to form a covalent compound with the formula XF .
3 • Reacts with non-metals / named non-
(d) B [1] metal
Diamond is formed by carbon. Carbon has the • An oxidising agent
electronic configuration of 2,4. • Forms acidic oxides
(e) C [1] (ii) Graphite
The electronic configuration of element C is 2,8,1. Physical property: [1]
Number 2 shows the number of electrons in the • A conductor of electricity
first shell. Number 8 shows the number of electrons • Soft
in the second shell. Number 1 shows the number of
electrons in the third shell. • Lubricant
• High melting point / High boiling point
(f) C [1] • Grey black / black solid
Metals are good conductors of electricity in general. • Slippery / Greasy
Element C is Group I element which is a metal. • Brittle / Breaks when subjected to stress
(g) E [1] • Insoluble in water
Element E is Group VII element. Halogens exist in
diatomic at room temperature.

Answers 161

Answers.indd 161 3/4/22 3:54 PM