Atomic Structure & The Periodic Table
1. A sample of chlorine contains two isotopes:
○ Cl-35 (75%)
○ Cl-37 (25%)
Calculate the relative atomic mass of chlorine. (3 marks)
Final Answer: 35.5
2. The first ionization energy of sodium is 496 kJ/mol, while for magnesium, it is 738
kJ/mol.
○ Explain why magnesium has a higher ionization energy than sodium. (3
marks)
Magnesium has a higher ionization energy than sodium because:
● Magnesium has a higher nuclear charge (more protons).
● Its outer electron is closer to the nucleus, experiencing stronger attraction.
● Sodium’s electron is in the third shell (3s¹), while magnesium’s is in the third shell
(3s²) but experiences more attraction due to a greater nuclear charge.
○
3. A metal X has an electronic configuration of 2,8,2.
○ Identify the element and state its position in the periodic table. (2 marks)
Element: Magnesium (Mg)
● Group 2 (2 valence electrons)
● Period 3 (3 energy levels)
○
4. Transition metals often form colored compounds.
○ Explain why transition metals show different colors in solution. (3 marks)
Transition metals form colored compounds due to d-orbital electron
transitions.When light passes through, some wavelengths are absorbed,
and the remaining light gives the compound its color.
5. The atomic number of an unknown element is 117.
Predict its group and period in the periodic table. (2 marks)
, Atomic number 117 → Group 17 (Halogens)
Period 7 (7 energy levels)
6. Why do noble gases have very low boiling points? (2 marks)
Weak van der Waals forces between atoms.Larger atoms (e.g., Xenon) have stronger
forces, leading to higher boiling points.
7. Write the full electron configuration of a sulfide ion (S²⁻). (2 marks)Sulfur (S)
atomic number = 16 → 2,8,6.Gains 2 electrons to form S²⁻ → 2,8,8
Chemical Bonding & Structure
Explain why graphite conducts electricity, but diamond does not. (3 marks)
Graphite has delocalized electrons that move freely, conducting electricity.
Diamond has no free electrons, so it does not conduct.
Compare and contrast the structure of sodium chloride (NaCl) and magnesium
chloride (MgCl₂). (3 marks)
NaCl: Simple ionic lattice, weaker electrostatic attraction.
MgCl₂: Stronger ionic bonds due to Mg²⁺ being smaller and more charged than Na⁺.
Silicon dioxide (SiO₂) is an important material in the electronics industry.
○ Describe its structure and bonding. (3 marks)
Giant covalent structure with strong Si-O bonds.High melting point due to
strong covalent bonding.
Why do simple covalent molecules have low melting and boiling points? (2 marks)
Weak intermolecular forces (London forces or dipole-dipole) lead to low
melting/boiling points.
Ionic compounds are usually soluble in water but insoluble in organic solvents.
Explain why. (2 marks)
Water is polar, attracting ions and dissolving them.
Non-polar solvents lack charge, so ionic compounds don’t dissolve.
1. A sample of chlorine contains two isotopes:
○ Cl-35 (75%)
○ Cl-37 (25%)
Calculate the relative atomic mass of chlorine. (3 marks)
Final Answer: 35.5
2. The first ionization energy of sodium is 496 kJ/mol, while for magnesium, it is 738
kJ/mol.
○ Explain why magnesium has a higher ionization energy than sodium. (3
marks)
Magnesium has a higher ionization energy than sodium because:
● Magnesium has a higher nuclear charge (more protons).
● Its outer electron is closer to the nucleus, experiencing stronger attraction.
● Sodium’s electron is in the third shell (3s¹), while magnesium’s is in the third shell
(3s²) but experiences more attraction due to a greater nuclear charge.
○
3. A metal X has an electronic configuration of 2,8,2.
○ Identify the element and state its position in the periodic table. (2 marks)
Element: Magnesium (Mg)
● Group 2 (2 valence electrons)
● Period 3 (3 energy levels)
○
4. Transition metals often form colored compounds.
○ Explain why transition metals show different colors in solution. (3 marks)
Transition metals form colored compounds due to d-orbital electron
transitions.When light passes through, some wavelengths are absorbed,
and the remaining light gives the compound its color.
5. The atomic number of an unknown element is 117.
Predict its group and period in the periodic table. (2 marks)
, Atomic number 117 → Group 17 (Halogens)
Period 7 (7 energy levels)
6. Why do noble gases have very low boiling points? (2 marks)
Weak van der Waals forces between atoms.Larger atoms (e.g., Xenon) have stronger
forces, leading to higher boiling points.
7. Write the full electron configuration of a sulfide ion (S²⁻). (2 marks)Sulfur (S)
atomic number = 16 → 2,8,6.Gains 2 electrons to form S²⁻ → 2,8,8
Chemical Bonding & Structure
Explain why graphite conducts electricity, but diamond does not. (3 marks)
Graphite has delocalized electrons that move freely, conducting electricity.
Diamond has no free electrons, so it does not conduct.
Compare and contrast the structure of sodium chloride (NaCl) and magnesium
chloride (MgCl₂). (3 marks)
NaCl: Simple ionic lattice, weaker electrostatic attraction.
MgCl₂: Stronger ionic bonds due to Mg²⁺ being smaller and more charged than Na⁺.
Silicon dioxide (SiO₂) is an important material in the electronics industry.
○ Describe its structure and bonding. (3 marks)
Giant covalent structure with strong Si-O bonds.High melting point due to
strong covalent bonding.
Why do simple covalent molecules have low melting and boiling points? (2 marks)
Weak intermolecular forces (London forces or dipole-dipole) lead to low
melting/boiling points.
Ionic compounds are usually soluble in water but insoluble in organic solvents.
Explain why. (2 marks)
Water is polar, attracting ions and dissolving them.
Non-polar solvents lack charge, so ionic compounds don’t dissolve.
