Key Concepts: Atoms contain protons, neutrons and electrons. Atomic number and mass number describe atomic structure. Bonding involves electron transfer (ionic) or sharing (covalent) and affects properties.
Section A: Atomic Structure
1. Define atom and molecule, and state the relative mass and charge of each sub-atomic particle. [5]
2. Define atomic number, mass number and isotope. [3]
3. Chlorine has two isotopes: Cl-35 (75%) and Cl-37 (25%). Calculate the relative atomic mass of chlorine. [2]
Section B: Ions and Ionic Bonding
4. State the charges of ions formed by Groups 1, 2, 3, 5, 6 and 7. [6]
5. Write formulae for: MgCl₂, Al₂O₃, Na₂S, Ca(NO₃)₂, (NH₄)₂SO₄. [5]
6. Draw dot-and-cross diagrams for NaCl and MgO. [4]
7. Explain ionic bonding and why ionic compounds have high melting points and conduct electricity when molten or aqueous. [4]
Section C: Covalent Bonding and Structures
8. Draw dot-and-cross diagrams for H₂, O₂, N₂, HCl, H₂O, NH₃ and CO₂. [7]
9. Explain why simple molecular substances have low melting and boiling points. [2]
10. Compare diamond, graphite and C₆₀ in terms of structure and properties. [4]
Total marks: 42
Mark Scheme
1. Atom: smallest particle of an element; molecule: two or more atoms bonded [2]. Proton +1 mass 1; neutron 0 mass 1; electron -1 mass ~0 [3]
2. Atomic number = protons; mass number = protons + neutrons; isotope = same atomic number, different mass number [3]
3. (35×0.75) + (37×0.25) = 35.5 [2]
4. Group 1: +1; Group 2: +2; Group 3: +3; Group 5: -3; Group 6: -2; Group 7: -1 [6]
5. Correct formulae (1 each) [5]
6. Correct ionic dot-and-cross for NaCl and MgO [4]
7. Electrostatic attraction between oppositely charged ions; giant lattice; strong forces; mobile ions when molten/aqueous allow conduction [4]
8. Correct covalent dot-and-cross diagrams [7]
9. Weak intermolecular forces require little energy to overcome [2]
10. Diamond: giant covalent, hard, no conduction; Graphite: layers, conducts; C60: simple molecular, low mp (any four points) [4]