GCSE Bonding, Structure and Properties of Matter (Chemistry) 2 — Questions and Answers
Question 1: Which statement best describes metallic bonding?
- A shared pair of electrons between two atoms
- The attraction between oppositely charged ions
- A regular arrangement of positive metal ions surrounded by a sea of delocalised electrons (Correct answer)
- Weak forces between neutral molecules
Correct answer: A regular arrangement of positive metal ions surrounded by a sea of delocalised electrons
Metals consist of a giant structure of positive ions in a sea of delocalised electrons; the electrostatic attraction between them is the metallic bond.
In a metal, the atoms are arranged in a regular giant lattice. The outer-shell electrons are delocalised, meaning they are free to move throughout the whole structure. The strong electrostatic attraction between the positive metal ions and the delocalised electrons holds the structure together. This model explains why metals conduct electricity and thermal energy (the electrons carry charge and energy) and why they are malleable (layers of ions can slide).
Question 2: Why is an alloy such as brass harder than pure copper?
- The different-sized atoms distort the layers, making it harder for them to slide over each other (Correct answer)
- Alloys contain ionic bonds, which are stronger
- The alloy has more delocalised electrons
- The atoms in an alloy are all the same size
Correct answer: The different-sized atoms distort the layers, making it harder for them to slide over each other
In a pure metal the layers of identical atoms slide easily; in an alloy, atoms of different sizes disrupt the regular layers so they cannot slide as easily.
Pure metals are relatively soft because their atoms are arranged in regular layers that can slide over each other when a force is applied. An alloy is a mixture of a metal with one or more other elements. The added atoms are a different size, which distorts the regular arrangement of layers so they can no longer slide easily. This makes alloys like brass (copper and zinc) and steel (iron with carbon) harder and more useful than the pure metals.
Question 3: A nanoparticle has a diameter of 50 nm. Which of these correctly expresses 50 nm in metres?
- 5 × 10⁻⁶ m
- 5 × 10⁻⁸ m (Correct answer)
- 5 × 10⁻⁹ m
- 5 × 10⁻¹⁰ m
Correct answer: 5 × 10⁻⁸ m
1 nm = 1 × 10⁻⁹ m, so 50 nm = 50 × 10⁻⁹ m = 5 × 10⁻⁸ m.
Nanoparticles are between 1 and 100 nm in size. One nanometre is 1 × 10⁻⁹ m, so 50 nm = 50 × 10⁻⁹ m. In standard form this is written 5 × 10⁻⁸ m (moving the decimal point one place makes the power of ten one larger). Nanoparticles have a very high surface area to volume ratio compared with bulk material, which gives them different properties and uses, such as in sunscreens and catalysts.
Question 4: Which change of state is called sublimation?
- Solid to liquid
- Liquid to gas
- Solid directly to gas (Correct answer)
- Gas directly to solid
Correct answer: Solid directly to gas
Sublimation is when a solid turns directly into a gas without passing through the liquid state, as with solid carbon dioxide (dry ice).
The changes of state are melting (solid to liquid), freezing (liquid to solid), boiling or evaporating (liquid to gas), condensing (gas to liquid), sublimation (solid to gas) and deposition (gas to solid). During any change of state, energy is transferred to or from the particles to change the forces between them, but the temperature stays constant until the change is complete.
Question 5: What is a limitation of the simple particle model used to describe solids, liquids and gases?
- It shows that particles are constantly moving
- It assumes particles are solid, inelastic spheres with no forces between them (Correct answer)
- It cannot explain why gases can be compressed
- It only applies to metals
Correct answer: It assumes particles are solid, inelastic spheres with no forces between them
The simple model treats particles as small solid spheres and does not show the forces between them or that particles are not actually solid.
The particle model represents each particle as a small, solid, inelastic sphere. Its limitations are that real particles are not solid spheres, they are mostly empty space with a nucleus and electrons; the model does not show the forces between particles; and it does not show that particles of a substance can be atoms, molecules or ions of different sizes. Despite this, it is useful for explaining changes of state, density and compressibility.
Question 6: Which type of structure does silicon dioxide (silica, SiO₂) have?
- Simple molecular
- Giant ionic
- Giant covalent (Correct answer)
- Metallic
Correct answer: Giant covalent
Silicon dioxide is a giant covalent structure in which each silicon atom bonds to four oxygen atoms and each oxygen to two silicon atoms.
Silicon dioxide, found in sand and quartz, is a giant covalent (macromolecular) structure. Each silicon atom is covalently bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a rigid three-dimensional network. Like diamond, it has a very high melting point because many strong covalent bonds must be broken to melt it, and it does not conduct electricity because it has no free electrons or ions.
GCSE Bonding, Structure and Properties of Matter (Chemistry) 2
Which statement best describes metallic bonding?