Properties of Materials (OCR GCSE Chemistry A (Gateway)): Flashcards

Simple molecular substances have weak intermolecular forces between their molecules. Only a small amount of energy is needed to overcome these forces, so they melt and boil at low temperatures.

True.

Freezing is the reverse of melting and occurs at exactly the same temperature. Water, for example, both melts and freezes at 0 °C.

Evaporation occurs only at the surface of a liquid, where high-energy particles can escape at temperatures below the boiling point.

Sublimation is the direct change of state from solid to gas, without passing through the liquid state. Iodine and solid carbon dioxide are examples of substances that sublime.

The stronger the forces of attraction between particles, the more energy is needed to overcome them. This means stronger forces give a higher melting point.

True.

Boiling occurs throughout a liquid at a fixed temperature, forming bubbles below the surface. Evaporation occurs only at the surface across a range of temperatures.

At 900 °C the substance is in the liquid state. This temperature is above its melting point (650 °C) and below its boiling point (1200 °C).

A substance is in the solid state at temperatures below its melting point, and in the gas state at temperatures above its boiling point.

Bulk properties are physical characteristics such as electrical conductivity and melting point that arise when many atoms, ions or molecules act together. Individual atoms do not possess these properties.

Ionic substances have a giant ionic lattice held together by very strong electrostatic forces between oppositely charged ions. A large amount of energy is needed to break these bonds, giving a high melting point.

True.

Metal atoms are arranged in orderly layers. When a force is applied, the layers slide over each other without breaking the metallic bonds, so the metal changes shape rather than cracking.

Ionic and giant covalent structures are brittle because applying force breaks their bonds, whereas metals are malleable because their layers can slide.

Simple covalent substances have no freely moving charged particles. Their electrons are all held in covalent bonds and there are no ions present. Without mobile charges, they cannot carry an electric current.

A malleable material can change shape when a force is applied without cracking or breaking. Metals are malleable because their atomic layers slide over each other.

False.

The intermolecular forces between polymer molecules are larger than those between simple covalent molecules, which is why polymers generally need more energy to melt.

Giant covalent substances have millions of strong covalent bonds extending throughout a lattice. An enormous amount of energy is needed to break enough of these bonds to change state, giving very high melting points.

A nanoparticle is a particle between 1 and 100 nanometres in diameter, usually containing only a few hundred atoms. They are much smaller than fine particles.

Nanoparticles have a very high surface area to volume ratio. This means a much greater proportion of their atoms are at the surface, which changes how they interact chemically and physically compared to bulk material.

False.

Nanoparticles have diameters of 1 to 100 nm. Fine particles have diameters of 100 to 2500 nm, so fine particles are larger.

As the size of a particle decreases, its surface area to volume ratio increases which makes nanoparticles particularly effective as catalysts.

Nanoscience is the study and research into the production and application of nanoparticles. It is a rapidly developing field with applications in medicine, electronics and materials science.

In nanoparticle form, titanium dioxide blocks UV light but leaves no white marks on the skin and provides better coverage. In bulk form the same compound is used as a white pigment in paints.

True.

Silver nanoparticles are sprayed onto fibres in medical clothing and surgical masks. They retain the flexibility of the fabric while adding the antibacterial properties of silver metal.

Fullerenes are used in medicine to deliver drugs to target areas, and in electronic circuitry due to their small size and unique properties.

Nanoparticles have not been in use long enough to detect any long-term side effects. They are also not easily disposed of by the body, and even low toxicity would be amplified by their high surface area to volume ratio.

False.

Nanoparticle science is still in its early stages. There is a lack of understanding about how they may affect health, particularly regarding long-term side effects that have not yet been detected.