Key Chemistry Terms: Alloys, Bonding, Structures & States

alloy

A mixture of two or more elements, at least one of which is a metal. Examples include bronze and brass.

aqueous

A substance dissolved in water. Shown as (aq) in chemical equations.

atom

The smallest part of an element that can exist.

ball and stick model

A model of a molecule that uses spheres to represent atoms and sticks to represent bonds.

boiling

The process that happens at the boiling point of a substance when the rate of evaporation is at its maximum.

boiling point

The temperature at which a substance changes from liquid to gas (evaporates). It is also the temperature at which a substance changes from gas to liquid (condenses).

bond

An attraction between atoms, ions or molecules that enables the formation of chemical compounds. Such attractions could be ionic, covalent or metallic.

Buckminsterfullerene

The first fullerene to be discovered. It has the chemical formula C60 and a spherical shape.

carbon nanotube

A cylindrical fullerene with a very high length to diameter ratio.

catalyst

A substance that increases the rate of a chemical reaction by lowering the activation energy without being used up in the reaction. In biological systems, enzymes act in this way.

charge

A property of a particle that causes it to experience a force in an electric field.

chemical formula

A series of chemical symbols showing the number of atoms of each element in a compound.

compound

A substance made up of two or more different elements chemically bonded together, e.g. water is a compound of hydrogen and oxygen.

condensation

A change of state from gas to liquid.

conduction

The transfer of heat or electricity through a material.

coarse particles

Particles with a diameter between 2500 and 10 000nm. Often referred to as dust.

covalent bond

The attraction between two atoms that share one or more pairs of electrons.

delocalised electron

A bonding electron that is no longer associated with any particular atom and therefore free to move through the structure.

diamond

A giant covalent structure in which each carbon atom forms covalent bonds with four other carbon atoms.

dot and cross diagram

A diagram showing the arrangement of the outer shell electrons of the atoms or ions in a substance.

electric current

The flow of electrical charge.

electronic structure

The number of electrons in each energy level (shell) of an atom, e.g. a sodium atom has an electronic structure of 2, 8, 1.

electron

A particle with a relative charge of -1 and a very small relative mass. It orbits the nucleus of an atom or ion in energy levels (shells).

electrostatic force

The attractive or repulsive force between two charged objects.

empirical formula

A formula that shows the proportions of the elements present in a compound but not the actual numbers.

fine particles

Particles with a diameter of 100 to 2500nm. Also called particulate matter.

freezing

A change of state from liquid to solid.

fullerene

A molecule of carbon atoms with a hollow shape. It has a cage-like structure based on hexagonal rings of carbon atoms.

gas

The state of matter in which a substance can flow and completely fill a container. It has no fixed shape or volume and can be compressed.

giant covalent structure

A huge 3D structure made up of many atoms held together by covalent bonds.

giant ionic lattice

A huge 3D structure in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.

graphene

A single layer of graphite.

graphite

A giant covalent structure in which each carbon atom forms covalent bonds with three other carbon atoms, forming layers of hexagonal rings with no covalent bonds between the layers.

intermolecular forces

The attraction between individual molecules in a covalently bonded substance.

ion

A charged particle formed when an atom or molecule loses or gains one or more electrons.

ionic bond

The electrostatic force of attraction between positively and negatively charged ions.

lattice

A closely-packed regular arrangement of atoms, ions or molecules.

liquid

The state of matter in which a substance can flow and take the shape of a container. It has a fixed volume and cannot be compressed.

lubricant

A substance that reduces the effects of friction by helping two surfaces move past each other more easily.

melting

A change of state from solid to liquid.

melting point

The temperature at which a substance changes from solid to liquid (melts). It is also the temperature at which a substance changes from liquid to solid (freezes).

metal

An element that forms positive ions.

metallic bond

The attraction between a metal ion and delocalised electrons.

molecular formula

A formula that shows the actual numbers of atoms of each element in a molecule.

molecule

A substance made of more than one atom held together by covalent bonds.

nanometre

A unit of length equal to 10-9 metres.

nanoparticle

A tiny particle or structure between 1 and 100 nanometres in size.

noble gas

An unreactive gas found in Group 0 of the periodic table.

non-metal

An element that forms negative ions.

outer shell

The energy level of an atom furthest from the nucleus.

particle model

A model that describes the arrangement and movement of particles in a substance.

polymer

A large molecule that consists of many repeating units (monomers).

pure metal

A metal consisting of a single element.

shell

The distance from the nucleus of an atom where electrons orbit. Also called an energy level.

small molecule

A molecule with no overall charge consisting of only a few atoms held together by covalent bonds.

solid

The state of matter in which a substance has a fixed shape and cannot flow or be compressed.

state symbol

An abbreviation used in a symbol equation to show if a reactant or product is a solid (s), liquid (l), gas (g) or dissolved in water (aq).

state of matter

The classification of a substance as solid, liquid or gas.

surface area

The total area of the surface of an object.

surface area to volume ratio

A measure of surface area compared to volume of a substance.

temperature

The average kinetic energy of the particles in a substance, measured in degrees Celsius (°C).

volume

The amount of space that a substance or object occupies.