Secondary 4 Pure Chemistry Atomic Structure Bonding Quiz

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Secondary 4 Pure Chemistry Quiz - Atomic Structure Bonding

Name: __________________________
Class: __________________________
Date: __________________________
Score: ________ / 45

Duration: 60 Minutes
Total Marks: 45

Instructions:

• Answer all questions in the spaces provided.
• For dot-and-cross diagrams, show only the valence shells unless otherwise stated.
• Use a ruler for all diagrams.

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Section A: Atomic Structure and Ion Formation (Questions 1–7)

1. An element $X$ forms an ion $X^{2+}$ which has a total of 10 electrons. Identify element $X$ and state its proton number. [2]
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2. Define the term isotope in terms of sub-atomic particles. [2]
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3. An atom of element $Y$ has 19 protons and 20 neutrons. (a) Write the nuclide notation for this atom. [1] \

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   (b) State the electronic configuration of the ion formed by element $Y$. [1] \

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4. Element $Z$ is in Group 17 of the Periodic Table. Describe how an atom of $Z$ achieves a stable electronic configuration. [2]
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5. Explain why the relative atomic mass of Chlorine is 35.5 rather than a whole number. [2]
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6. An ion $M^+$ has only three completely filled shells of electrons. Identify the element $M$. [2]
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7. Compare the size of a sodium atom ($\text{Na}$) with a sodium ion ($\text{Na}^+$). Explain your answer. [2]
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Section B: Chemical Bonding (Questions 8–14)

8. Draw a dot-and-cross diagram to show the bonding in a molecule of water ($\text{H}_2\text{O}$). [3]
   
   
   
   
   
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9. Describe the formation of an ionic bond between a Magnesium atom and an Oxygen atom. [3]
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10. Draw a dot-and-cross diagram for the electronic structure of Magnesium Chloride ($\text{MgCl}_2$). [3]
    
    
    
    
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11. Explain the term "electrostatic attraction" in the context of ionic bonding. [2]
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12. Carbon tends to form covalent compounds. Draw a dot-and-cross diagram for methane ($\text{CH}_4$) and state the number of covalent bonds formed. [3]
    
    
    
    
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13. Describe metallic bonding in terms of the arrangement of ions and electrons. [2]
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14. Why are covalent bonds considered "strong" while the forces between simple molecular covalent substances are "weak"? [2]
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Section C: Structure and Properties (Questions 15–20)

15. Explain, in terms of structure and bonding, why graphite is used as a lubricant in machinery. [3]
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16. Diamond and Silicon(IV) oxide both have giant covalent structures. Explain why diamond is significantly harder than most other materials. [3]
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17. Explain why Copper is able to conduct electricity in the solid state. [3]
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18. Sodium chloride ($\text{NaCl}$) conducts electricity when molten but not when solid. Explain this observation. [3]
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19. Compare the melting points of Diamond and Iodine ($\text{I}_2$). Explain the difference based on their structures. [4]
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20. A substance $W$ has a high melting point, does not conduct electricity in any state, and is very hard. Deduce the type of structure $W$ possesses and provide an example of such a substance. [2]
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Answer Key - Secondary 4 Pure Chemistry Quiz: Atomic Structure Bonding

Section A: Atomic Structure and Ion Formation

1. Element: Magnesium ($\text{Mg}$); Proton Number: 12. (10 electrons in $\text{X}^{2+}$ means the atom had 12). [2]
2. Atoms of the same element with the same number of protons but different numbers of neutrons. [2]
3. (a) $^{39}_{19}\text{K}$ [1] (b) 2, 8, 8 [1]
4. It gains one electron from another atom to complete its outer shell (achieving a noble gas configuration). [2]
5. Chlorine exists as a mixture of isotopes (mainly $\text{Cl}-35$ and $\text{Cl}-37$). The relative atomic mass is the weighted average of these isotopes. [2]
6. Element: Potassium ($\text{K}$). (Three filled shells = 2, 8, 8 = 18 electrons. $\text{M}^+$ has 18, so atom had 19). [2]
7. $\text{Na}^+$ is smaller than $\text{Na}$. The sodium atom loses its entire outer shell of electrons to form the ion. [2]

Section B: Chemical Bonding

8. Diagram: Oxygen center with 6 valence electrons (2 lone pairs, 2 shared pairs with H). H atoms each sharing 1 electron. [3]
9. Magnesium atom loses 2 valence electrons to form $\text{Mg}^{2+}$. Oxygen atom gains these 2 electrons to form $\text{O}^{2-}$. The strong electrostatic attraction between the oppositely charged ions forms the ionic bond. [3]
10. Diagram: $\text{Mg}^{2+}$ in brackets (empty valence shell shown or 2,8). Two $\text{Cl}^-$ ions in brackets, each with 8 electrons (7 dots, 1 cross from Mg). [3]
11. The force of attraction between two oppositely charged particles (cations and anions). [2]
12. Diagram: Carbon center with 4 shared pairs of electrons with 4 Hydrogen atoms. Bonds: 4 covalent bonds. [3]
13. A lattice of positive metal ions surrounded by a "sea" of delocalized electrons. [2]
14. Covalent bonds are strong because they involve the strong attraction between nuclei and shared pairs of electrons. Forces between molecules (intermolecular forces) are weak van der Waals forces. [2]

Section C: Structure and Properties

15. Graphite has a layered structure. Each carbon is bonded to 3 others in hexagonal rings. There are weak forces between layers, allowing them to slide over each other. [3]
16. Diamond has a giant covalent structure where each carbon atom is bonded to 4 others in a rigid 3D tetrahedral lattice. Many strong covalent bonds must be broken to deform the structure. [3]
17. Copper has metallic bonding with a sea of delocalized electrons. These electrons are free to move throughout the structure to carry electrical charge. [3]
18. In solid $\text{NaCl}$, ions are fixed in a giant ionic lattice and cannot move. When molten, the lattice breaks down, allowing ions to move freely and conduct electricity. [3]
19. Diamond has a much higher melting point. Diamond is a giant covalent structure with many strong covalent bonds requiring huge energy to break. Iodine is a simple molecular structure with only weak intermolecular forces between molecules. [4]
20. Structure: Giant Covalent Structure. Example: Diamond or Silicon(IV) oxide. [2]