Bonding, Structure and the Properties of Matter
What's covered
Key facts
Alloys are harder than pure metals because different-sized atoms disrupt the lattice, stopping layers sliding over each other.
Giant covalent structures have higher melting points than simple molecular ones because many strong covalent bonds must be broken.
A covalent bond is a chemical bond formed when two atoms share a pair of electrons.
In diamond, each carbon atom forms four strong covalent bonds to four neighbouring carbon atoms in a rigid 3D tetrahedral lattice.
A chloride ion (Cl⁻) carries a charge of −1.
A metallic bond is the strong attraction between positive metal ions and a "sea" of delocalised electrons.
Graphene is a single layer of carbon atoms arranged in a hexagonal lattice; it is very strong and conducts electricity.
Alloys are harder than pure metals because different-sized atoms stop layers sliding.
Giant covalent structures have very high melting points because many strong covalent bonds throughout the structure must all be broken.
Covalent bonds form between non-metal atoms. Ionic bonds form between a metal and a non-metal.
Sample questions
A taste of the 83 questions in this topic — answers marked. Sign up to practise the full set with spaced repetition.
Why are alloys harder than pure metals?
- •Alloys contain fewer delocalised electrons, holding ions more rigidly
- •Alloys form stronger ionic bonds than pure metals because of different charges
- ✓Different-sized atoms disrupt the lattice, stopping layers sliding over each other
- •The added element donates extra electrons, increasing bonding strength
Why do simple molecules have low melting points?
- •Few atoms exist within each molecule
- •Molecules contain no electrons at all
- •Weak covalent bonds inside molecules
- ✓Weak intermolecular forces between molecules
Why do simple molecular substances such as water and oxygen have low melting points?
- •Simple molecular substances always have very low relative formula masses
- •The covalent bonds within the molecules are weak and break easily
- •Their atoms have few outer electrons, weakening electrostatic attraction
- ✓Weak intermolecular forces between molecules need little energy to overcome
Why does diamond have a high melting point?
- •Delocalised electrons hold it together
- ✓Many strong covalent bonds throughout
- •Strong ionic bonds between atoms
- •Weak forces between molecules
What type of bonding is formed between sodium and chlorine?
- •Covalent — the two atoms share a pair of electrons equally
- •Hydrogen bonding — weak electrostatic attraction between partial charges
- ✓Ionic — Na transfers an electron to Cl, forming oppositely charged ions
- •Metallic — electrons are delocalised across both atoms
Why can metals conduct electricity?
- •Metal atoms have very small nuclei that let charge pass through
- •Metal ions are positively charged and attracted to electricity
- ✓Metals have delocalised electrons that can move freely and carry charge
- •Metals have ionic bonds that allow electrons to flow
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