Answers to Practise Questions (Basic) – Atomic

Answers to Practise Questions (Basic) – Atomic Structure and Bonding
Practise questions (Basic) are designed to ensure that students are aware of the basic
concepts of the topic. This should be the first step that students undertake while
revising for their chemistry examination. For the O Level examination, these basic
concepts will be tested although questions will not be straight forward and students
will need to be able to apply these concepts to solve the questions. For the chapter of
ammonia, there are fewer questions as this is a relatively small chapter and the scope
is much narrower.
(1): Write down the number of electrons and neutrons of the below particles:
(i):
Na+
(Nucleon number: 23 , Proton number: 11 )
Neutron – 12
Electron - 10
(ii): C
(Nucleon number: 12 , Proton number: 6 )
Neutron – 6
Electron – 6
(iii): C
(Nucleon number: 14 , Proton number: 6 )
Neutron - 8
Electron - 6
(iv): Al3+
(Nucleon number: 27 , Proton number: 13 )
Neutron – 14
Electron - 10
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(v): S2-
(Nucleon number: 32 , Proton number: 16 )
Neutron – 16
Electron - 18
(vi): Cl
(Nucleon number: 35 , Proton number: 17 )
Neutron – 18
Electron - 17
(vii): Cl
(Nucleon number: 37 , Proton number: 17 )
Neutron – 20
Electron - 17
(2): State what is an isotope and give examples of an isotope.
An isotope is an atom with the same proton number but different number of
neutrons.
Chlorine exists as Cl-35 and Cl-37 with neutron number of 18 and 20 respectively
Carbon exists as C-12, C-13 and C-14 with neutron number of 6, 7 and 8
respectively.
(3): State and explain whether an isotope of an atom has similar physical and
chemical properties
Isotope of an atom has similar chemical properties but different physical properties.
As the number of electrons of an isotope of an atom remains unchanged, the
chemical properties will be identical.
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(4): State how does metals and non-metals attain the stable electronic configuration
of a noble gas
Metals attain a stable electronic configuration by losing electron(s).
Non-metals attain a stable electronic configuration by gain electron(s) or sharing
electron(s).
(5): Draw dot and cross diagrams for the below:
(i): Carbon dioxide
(ii): Oxygen gas
(iii): Sodium oxide
(iv): Nitrogen gas
(v): Magnesium chloride
(6): State the chemical structures of the following:
(i): Graphite
Giant molecular structure
(ii): Water
Simple molecular structure
(iii): Lithium oxide
Giant ionic structure
(iv): Magnesium
Giant metallic structure
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(v): Iron
Giant metallic structure
(vi): Silicon dioxide
Giant molecular structure
(vii): Magnesium chloride
Giant ionic structure
(viii):Diamond
Giant molecular structure
(ix): Methane
Simple molecular structure
(7): State three physical properties of ionic compounds
High melting and boiling points
Soluble in water but insoluble in organic solvents
Conduct when molten or dissolved in water
(8): State three physical properties of simple molecular compounds
Low melting and boiling points
Soluble in organic solvents but insoluble in water
Does not conduct electricity in any state
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(9): State three physical properties of giant molecular compounds
High melting and boiling points
Does not conduct electricity in any state (except graphite)
Insoluble in both water and organic solvent
(10): Explain why does sodium chloride has high melting points.
Sodium chloride has a giant ionic structure. This consists of oppositely charged Na+
and Cl- held together by strong electrostatic forces of attraction (ionic bond). A lot of
energy is required to overcome the ionic bonds thus sodium chloride has high
melting points.
(11): Explain why ionic compounds are soluble in water.
Ionic compounds has a giant ionic structure consists of oppositely charged ions held
together by ionic bond. The polar molecules of water are attracted to the ions and the
energy released allows the ions to break free from the ionic structure. Thus ionic
compounds are soluble in water.
(12): Explain why magnesium chloride is only able to conduct electricity in the
molten state or when dissolved in water.
Magnesium chloride has a giant ionic structure. In the solid state, the ions are held in
fixed position by the ionic bond and thus are not able to move to conduct electricity.
Once dissolved in water, the ions are mobile and are able to move to conduct
electricity.
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(13): State the structure of iron and explain why it is able to conduct electricity in the
solid state.
Iron has a giant metallic structure. This consists of a lattice structure held together by
forces of attraction between metal cations and sea of mobile electrons. In the solid
state, the mobile electrons are free to move and thus metal is able to conduct
electricity in the solid state.
(14): Explain why carbon dioxide has low melting points and is not able to conduct
electricity in any state.
Carbon dioxide has a simple molecular structure. This consists of discrete molecules
held together by weak intermolecular forces. Little energy is required to overcome the
weak intermolecular forces and thus carbon dioxide has low melting points.
In carbon dioxide, all the valence electrons are involved in covalent bonding. Thus,
there are no mobile electrons available to conduct electricity. Hence, carbon dioxide
is not able to conduct electricity in any state.
(15): Describe the structure of graphite and explain why it is used as a lubricant.
Graphite has a giant molecular structure. This consists of carbon atoms arranged in
hexagonal ring layers with weak intermolecular forces between layers. Little energy
is required to overcome the weak intermolecular forces and thus the layer is able to
slide over each other with a small application of force. Graphite is thus slippery and
suitable for use as a lubricant.
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(16): Explain why graphite is able to conduct electricity while diamond is not able to.
Graphite has a giant molecular structure. This consists of carbon atoms arranged in
hexagonal ring in a layered arrangement. Within each layer, each carbon atom is
covalently bonded to three other carbon atoms. There is one electron that is not used
for bonding and this electron is mobile and is able to move to conduct electricity.
Diamond has a giant molecular structure, with each carbon atom covalently bonded
to 4 other atoms in a tetrahedral arrangement. As all the valence electrons of the
carbon atom are involved in covalently bonding, there is no electron that is free to
move to conduct electricity. Thus diamond is not able to conduct electricity.
(17): State the structure of diamond and explain why it has high melting points and
is insoluble in both water and organic solvents.
Diamond has a giant molecular structure, with each carbon atom covalently bonded
to 4 other atoms in a tetrahedral arrangement. A lot of energy is required to
overcome the strong covalent bond and thus diamond has high melting points.
Due to the strong covalent bond between carbon atoms, the attraction between the
solvent molecule and the carbon atom is not strong enough to overcome the strong
covalent bond. Thus, diamond is insoluble in water and organic solvents.
About Breeze Education:
Breeze Education offers chemistry tuition to O Level Students. Tuition classes are
conducted in small group to facilitate active discussion and consultation. Chemistry is
taught in a way to facilitate easy understanding of the topic. Students are also honed
on their revision techniques so that they can improve faster over a shorter period of
time. Tuition sessions are planned and taught by Dr Francis who has a PhD in
Biomedical Science from National University of Singapore. Lesson is conducted in
Yishun with direct bus connecting to Sembawang and Woodlands.
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