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Atoms, Elements and Compounds | IGCSE Chemistry (0620)

Atoms, Elements and Compounds | IGCSE Chemistry (0620) | SM-Educate
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CS-991 · Module I-3

2 · Atoms, Elements and Compounds

Cambridge IGCSE Chemistry 0620 · Core + Supplement · 2026–2028
Quick Revision
⚛ Atomic Structure 🔄 Isotopes 🔌 Ionic Bonding🧨 Covalent Bonding

2.1 Elements, Compounds and Mixtures Core

  • Element: Pure substance, one type of atom.
  • Compound: Two or more elements chemically combined, fixed proportion.
  • Mixture: Physically combined, variable proportion, separable by physical methods.
🎥 Video lectures for this sub-topic — coming soon
Q1: A pure substance made of only one type of atom is a(n):
a) Compound b) Mixture c) Element d) Solution
Show Answer
✅ c) Element
Q2: Which of these can be separated by physical methods?
a) A compound b) A mixture c) An element d) None of these
Show Answer
✅ b) A mixture

2.2 Atomic Structure and the Periodic Table Core

  • Nucleus: Protons (+1) + Neutrons (0) | Electrons (-1) in shells.
  • Proton number (Z) = number of protons | Mass number (A) = protons + neutrons.
  • Electronic configuration for first 20 elements (e.g., Na = 2,8,1).
  • Group number = outer electrons | Period number = electron shells.
🎥 Video lectures for this sub-topic — coming soon
Q1: The mass number of an atom equals:
a) Protons only b) Protons + Neutrons c) Neutrons only d) Protons + Electrons
Show Answer
✅ b) Protons + Neutrons
Q2: The electronic configuration of sodium (Na) is:
a) 2,8 b) 2,8,1 c) 2,8,8 d) 2,8,2
Show Answer
✅ b) 2,8,1

2.3 Isotopes Core + Supplement

  • Isotopes: Same protons, different neutrons (e.g., C-12, C-14).
  • Same chemical properties (same electronic configuration).
  • Relative atomic mass (Ar) calculation from isotopic abundances.
🎥 Video lectures for this sub-topic — coming soon
Q1: Isotopes of the same element have the same number of:
a) Neutrons b) Protons c) Mass number d) All of these
Show Answer
✅ b) Protons
Q2: Isotopes have the same chemical properties because they have the same:
a) Number of neutrons b) Mass number c) Electronic configuration d) Physical state
Show Answer
✅ c) Electronic configuration

2.4 Ions and Ionic Bonds Core + Supplement

  • Cations (+): Lose electrons | Anions (-): Gain electrons.
  • Ionic bond: Electrostatic attraction between oppositely charged ions.
  • Giant lattice structure: High melting/boiling points, conducts when molten/aqueous.
  • Dot-and-cross diagrams for ionic compounds (e.g., NaCl, MgO).
🎥 Video lectures for this sub-topic — coming soon
Q1: A cation is formed when an atom:
a) Gains electrons b) Loses electrons c) Gains neutrons d) Loses protons
Show Answer
✅ b) Loses electrons
Q2: Ionic compounds conduct electricity when:
a) Solid only b) Molten or dissolved in water c) Never d) At any temperature as a solid
Show Answer
✅ b) Molten or dissolved in water

2.5 Simple Molecules and Covalent Bonds Core + Supplement

  • Covalent bond: Sharing of a pair of electrons (non-metals).
  • Simple molecules: H₂, Cl₂, O₂, H₂O, CH₄, NH₃, HCl, CO₂.
  • Low melting/boiling points (weak intermolecular forces).
  • Poor electrical conductivity (no free ions/electrons).
🎥 Video lectures for this sub-topic — coming soon
Q1: A covalent bond involves:
a) Transfer of electrons b) Sharing of a pair of electrons c) Loss of a proton d) Gain of a neutron
Show Answer
✅ b) Sharing of a pair of electrons
Q2: Simple covalent molecules typically have:
a) High melting points b) Low melting points c) Good electrical conductivity d) Giant lattice structures
Show Answer
✅ b) Low melting points

2.6 Giant Covalent Structures Core + Supplement

  • Diamond: 4 covalent bonds per carbon → very hard, high melting point.
  • Graphite: 3 covalent bonds + delocalised electrons → conducts electricity, lubricant.
  • Silicon(IV) oxide (SiO₂): Similar to diamond, hard, high melting point.
  • Uses: Diamond (cutting tools), Graphite (electrodes, lubricant).
🎥 Video lectures for this sub-topic — coming soon
Q1: Graphite conducts electricity because it has:
a) Ionic bonds b) Delocalised electrons c) No electrons d) Only single bonds
Show Answer
✅ b) Delocalised electrons
Q2: Diamond is very hard because each carbon atom forms:
a) 2 covalent bonds b) 3 covalent bonds c) 4 covalent bonds d) No covalent bonds
Show Answer
✅ c) 4 covalent bonds

2.7 Metallic Bonding Supplement (Extended)

  • Metallic bond: Electrostatic attraction between positive ions and "sea" of delocalised electrons.
  • Good electrical conductivity (delocalised electrons move).
  • Malleable and ductile (layers of ions can slide).
🎥 Video lectures for this sub-topic — coming soon
Q1: Metals are good conductors of electricity because of:
a) Fixed ions b) Delocalised electrons that can move c) Covalent bonds d) No charged particles
Show Answer
✅ b) Delocalised electrons that can move
Q2: Metals are malleable because:
a) Layers of ions can slide over each other b) They have covalent bonds c) They have no electrons d) They are always liquid
Show Answer
✅ a) Layers of ions can slide over each other
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