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4.5Chemistry 01. Materials And Their Structure

Describe a covalent bond as a bond made when a pair of electrons is… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 6 parts Lesson 5 of 11 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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Lesson summary

4.5 Covalent bonds and molecules — CHECKPOINT - Lower Secondary Science 0893 notes: Describe a covalent bond as a bond made when a pair of electrons is shared between two atoms, and recognise covalent molecules and their formulae.Covalent bond — a bond made when a pair of electro…

  • Dot and cross diagram
  • Same non-metal
  • Different non-metals
  • Outermost shell
  • Covalent bond — a bond made when a pair of electrons is shared between two atoms.It forms between non-metal atoms
  • Molecule — a particle made of atoms joined by covalent bonds

Section 1 of 6Covalent bonding

  • Covalent bond
    • a bond made when a pair of electrons is shared between two atoms.
    • It forms between non-metal atoms.
  • Reason
    • sharing electrons gives each atom a full outermost electron shell, which is more stable.
    • The first shell holds only two electrons and the second and third shells hold eight.
  • Molecule
    • a particle made of atoms joined by covalent bonds.

Section 2 of 6Dot and cross diagrams

  • Dot and cross diagram
    • shows the outer electrons of one atom as dots and of the other as crosses.
    • The shared pair sits between the two atoms.

Section 3 of 6Examples of covalent molecules

SubstanceFormulaAtomsPairs shared
Hydrogen chlorideHCl1 hydrogen and 1 chlorine1 pair
HydrogenH22 hydrogen1 pair
ChlorineCl22 chlorine1 pair
AmmoniaNH31 nitrogen and 3 hydrogen3 pairs
MethaneCH41 carbon and 4 hydrogen4 pairs
WaterH2O2 hydrogen and 1 oxygen2 pairs
Carbon dioxideCO21 carbon and 2 oxygen4 pairs

Section 4 of 6How hydrogen chloride forms

  1. A hydrogen atom has one electron in its outer shell, which has room for two.
  2. A chlorine atom has seven electrons in its outer shell, which has room for eight.
  3. The atoms share one pair of electrons.
  4. Both atoms now have full outer shells and a molecule of HCl is formed.

Section 5 of 6How ammonia forms

  1. A nitrogen atom has five electrons in its outer shell.
  2. Three hydrogen atoms each share one electron with the nitrogen atom.
  3. Three pairs of electrons are shared.
  4. All the atoms have full outer shells and a molecule of NH3 is formed.

Section 6 of 6Elements and compounds that are covalent

  • Same non-metal
    • atoms of the same element join to form molecules such as H2, O2 and Cl2.
  • Different non-metals
    • atoms of different non-metals form covalent compounds such as CO2.

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