Atoms, Elements and CompoundsCambridge IGCSE Chemistry: Topic test

20 questions, 54 marks

Cambridge IGCSE Chemistry

Atoms, Elements and Compounds topic test

Total 54 marks

Name

Class

Date

1
A chemist examines three white solids, P, Q and R. Solid P is found to consist of only one type of atom. Solid Q is found to consist of two different elements chemically combined together in a fixed ratio, which cannot be separated by physical means. Solid R is found to be a physical mixture of solid P together with common salt, and the salt can be separated from solid R simply by dissolving it in water and filtering.
(a)
Which solid is a compound?
[1 mark]
ASolid P
BSolid Q
CSolid R
DNone of them
(b)
Which statement correctly explains why the salt can be separated from solid R by dissolving and filtering, but the elements in solid Q cannot be separated in the same way?
[1 mark]
ASolid R is a mixture, so its components are not chemically bonded and can be physically separated; solid Q is a compound, so its elements are chemically combined and cannot be separated by physical methods
BSolid R is a compound and solid Q is a mixture
CBoth R and Q are mixtures, but R dissolves in water and Q does not
DThe salt in R is radioactive, allowing it to be filtered out easily
(c)
State one difference between a mixture and a compound in terms of how their components are joined together, and explain how this difference relates to being able to separate the components physically.
[2 marks]
Total for question 1: 4 marks
2
An atom of the element aluminium has a proton number of 13 and a nucleon number of 27.
(a)
What is the electronic configuration of a neutral atom of aluminium?
[1 mark]
A2,8,2,1
B2,10,1
C2,8,3
D13,0,0
(b)
How many neutrons are there in this atom of aluminium?
[1 mark]
A13
B14
C27
D40
(c)
A second sample is found to contain a small proportion of atoms of aluminium with a nucleon number of 26 instead of 27, although both types of atom have the same proton number. State what these two types of atom are called, and explain, in terms of subatomic particles, how they differ from each other.
[2 marks]
Total for question 2: 4 marks
3
Magnesium (proton number 12, electronic configuration 2,8,2) reacts with chlorine (proton number 17, electronic configuration 2,8,7) to form the ionic compound magnesium chloride.
(a)
Describe, in terms of electron transfer, how the ions in magnesium chloride are formed from atoms of magnesium and chlorine, and state the formula of the compound formed.
[3 marks]
(b)
Explain, in terms of structure and bonding, why solid magnesium chloride does not conduct electricity but molten magnesium chloride does conduct electricity.
[4 marks]
Total for question 3: 7 marks
4
A materials scientist compares two forms of solid carbon, diamond and graphite, both giant covalent structures, with a sample of solid carbon dioxide (dry ice), which is a simple molecular substance made of individual CO2 molecules held together by weak intermolecular forces.
(a)
Explain, in terms of structure and bonding, why diamond has an extremely high melting point, while solid carbon dioxide sublimes at a much lower temperature.
[6 marks]
(b)
Graphite, the other giant covalent form of carbon, conducts electricity, but diamond does not, even though both are giant covalent structures of the same element. Explain this difference in terms of structure and bonding, and suggest why graphite, rather than diamond, is used as an electrode in electrolysis.
[6 marks]
Total for question 4: 12 marks
5
A metallurgist compares a pure sample of copper metal with a sample of the ionic compound copper(II) oxide. Copper metal is described as having a giant metallic structure of copper ions surrounded by a 'sea' of delocalised electrons.
(a)
Which statement correctly describes the bonding in a pure metal such as copper?
[1 mark]
ACopper ions are held in a regular lattice by strong electrostatic attraction to a sea of delocalised electrons that are free to move throughout the structure
BCopper atoms share pairs of electrons with neighbouring atoms in individual molecules
CCopper ions are held together only by weak intermolecular forces between separate copper atoms
DCopper atoms are held in fixed positions with no free electrons present
(b)
Which property of copper metal is best explained by the presence of delocalised electrons that are free to move throughout the structure?
[1 mark]
AIts high density
BIts good electrical conductivity
CIts lack of reactivity with oxygen
DIts resistance to being drawn into wires
(c)
Explain, in terms of structure and bonding, why copper metal can be hammered into different shapes (is malleable) without shattering, unlike an ionic compound such as copper(II) oxide.
[2 marks]
Total for question 5: 4 marks
6
A student compares two covalently bonded gases, methane, CH4, and hydrogen chloride, HCl. In methane, a carbon atom shares one pair of electrons with each of four hydrogen atoms. In hydrogen chloride, one hydrogen atom shares one pair of electrons with one chlorine atom.
(a)
What is the total number of covalent bonds present in a single molecule of methane, CH4?
[1 mark]
A1
B2
C3
D4
(b)
Which statement correctly describes why methane has a low boiling point?
[1 mark]
AThe covalent bonds within each methane molecule are weak and easily broken on boiling
BMethane molecules are held together by weak intermolecular forces, which require little energy to overcome
CMethane has a giant covalent structure with weak bonds throughout
DMethane ions are only weakly attracted to each other
(c)
Describe how the covalent bond in hydrogen chloride, HCl, forms, and state whether hydrogen chloride has a high or low melting point, giving a reason based on its structure.
[2 marks]
Total for question 6: 4 marks
7
A furnace engineer compares silicon(IV) oxide, SiO2, a giant covalent structure used to line furnaces, with a sample of solid iodine, I2, a simple molecular substance.
(a)
Describe the structure of silicon(IV) oxide, and explain why it has a very high melting point.
[3 marks]
(b)
Explain why silicon(IV) oxide is suitable for lining a furnace that reaches very high temperatures, and explain why solid iodine, in contrast, would not be suitable for this purpose, in terms of structure and bonding.
[4 marks]
Total for question 7: 7 marks
8
A chemist compares sodium fluoride, an ionic compound formed between sodium (proton number 11) and fluorine (proton number 9), with a sample of naturally occurring fluorine, which is found to consist of only one type of atom, all with a nucleon number of 19, unlike some other elements which occur as mixtures of isotopes.
(a)
Explain, using electronic configurations, how the ions in sodium fluoride are formed from atoms of sodium and fluorine, and describe the structure of solid sodium fluoride and how this structure is held together.
[6 marks]
(b)
Explain what is meant by stating that naturally occurring fluorine consists of only one type of atom, and explain, using a named example, what it would mean if a sample of an element instead consisted of a mixture of isotopes, including how this would affect the calculation of its relative atomic mass.
[6 marks]
Total for question 8: 12 marks

End of questions