Chemistry Definition List

Element – a substance consists of one type of atom.

 Compound – a substance consists two or more elements that are chemically bonded (molecule or ions).

 Atom – smallest particle of an element.

 Molecule – a group of two or more atoms.

 Ion – a positively charged / negatively charged particle.

 Boiling point - Temperature at which liquid changes to gas under standard pressure.

 Melting point - Temperature at which solid changes to liquid under standard pressure.

 Isotopes – atoms of the same element with same proton number but different nucleon numbers.

 Matter（solid，liquid，gas）

 Particles（atom，molecules，ions）

 Subatomic particle – proton，neutron，electron

 Number of neutron（√），neutron number（×）

 Proton number – the number of proton in its atom.

 Nucleon number – the total number of proton and neutron in its atom.

 Relative atomic mass of an element = the average mass of one atom of an element/((1/12) x the mass of one carbon-12 atom).

 Relative molecular mass of an element = the average mass of one atom of an molecule/((1/12) x the mass of one carbon-12 atom).

 Molecule formula – compound shows the actual number of atoms of each element that are present in a molecule of the compound.

 Empirical formula – compound shows the simplest whole number ratio of atoms of each element in the compound.

 Mole – amount of substance that contains as many particles as the number of atoms in exactly 12 g of carbon-12 the symbol of mole is mol.

 One mole – Avogadro constant – 6.02 x 1023

 Group (Periodic Table) – vertical columns of element (similar chemical properties).

 Periods (Periodic Table) – horizontal rows of element.

 Valence electrons – electrons that occupy the outermost shell.

 Ionic bond – bond formed through the transfer of electrons between atoms of metal and non-metal to achieve the stable octet electron arrangement.

 Ionic compound – consist of positive ions and negative ions which are held by strong electrostatic forces of attraction.

 Covalent bond – bond formed through the sharing of electrons between atoms of non-metal to achieve the stable duplet or octet electron arrangement.

 Covalent compound (also simple molecular structure) – consists of neutral molecules which are held by weak intermolecular forces (Van der Waals).

 Electrolysis – The process of breaking down chemical compounds via the use of electric current.

 Anion – Negatively charged ions.

 Cation – Positively charged ions.

 Halogen – salt former with metals.

 Alkali (base) – chemical substance which ionizes in water to produce hydroxide ions, OH^-.

 Acid – chemical substance which ionizes in water to produce hydrogen ions, H⁺ or hydroxonium ions, H₃O⁺.

 pH – degree of acidity or alkalinity of a solution. Scale ranges from 0 to 14.

 pH value – measure of the concentration of hydrogen ions, H⁺ / hydroxide ions,OH^-.

 Strong alkali – ionises (dissociates) completely in water to form high concentration of hydroxide ions, OH^-.

 Weak alkali – ionises (dissociates) partially in water to form low concentration of hydroxide ions, OH^-.

 Strong acid – ionises (dissociates) completely in water to form high concentration of hydrogen ions, H⁺.

 Weak acid – ionises (dissociates) partially in water to form low concentration of hydrogen ions, H⁺.

 Neutralisation – the reaction between acid and base to produce salt and water only.

 Titration – a experiment used to determine the volume of acid needed to neutralize a fixed volume and molarity of alkali in a conical flask with the help of an acid-base indicator to detect the end point of the neutralization.

 Salt – a ionic compound formed when the hydrogen ion , H⁺ from acid is replaced by a metal ion / ammonium ion , NH₄⁺.

 Alloy – The compound that is formed by mixing metals with other elements.

 Polymer – long chain molecules made up by monomer (repeating unit).

 Rate of reaction –speed at which reactant are converted into products in a chemical reaction.

 Effective collision (Collision theory) – collision that results in a chemical reaction where the particles collide with the correct orientation and are able to achieve the activation energy.

 Catalyst – a chemical substances that provide an alternative path to lower the activation energy and increase the rate of reaction.

 Positive catalyst – increases the rate of reaction & lower the activation energy.

 Negative catalyst – decreases the rate of reaction & higher the activation energy.

 Homologous series – organic compounds (families) with similar formulae and properties.

 Organic compounds – carbon-containing compound. Carbon atoms form covalent bonds.

 Inorganic compounds – compounds from non-living things which do not contain the element carbon.

 Saturated hydrocarbons – hydrocarbons containing only single bonds between all carbon atoms.

 Unsaturated hydrocarbons – hydrocarbons containing at least one carbon-carbon double or triple bond.

 Isomer – Molecule that has same molecular formula but different structural formula.

 Esterification – esters are produced.

 Vulcanisation – a process of hardening  of natural rubber by adding sulphur compounds.

 Redox reaction – chemical reactions involving oxidation and reduction occurring simultaneously.

 Exothermic reaction – chemical reaction that release heat to the surroundings.

 Endothermic reaction – chemical reaction that absorbs heat from the surroundings.

 Heat of precipitation – the heat change when one mole of a precipitate is formed from their ions in aqueous solution.

 Heat of displacement – the heat change when one mole of a metal is displaced from its salt solution by a more electropositive metal.

 Heat of neutralisation – the heat change when one mole of water is formed from the reaction between an acid and an alkali.

 Heat of combustion – the heat change when one mole of a substance is completely burnt in excess oxygen.

 Flavouring – improve the taste or smell of food and restore taste loss due to food processing.

 Stabilisers – help to mix two liquids that usually do not mix together so that they form an emulsion.

 Thickeners – substances that thicken food and give the food a firm, smooth and uniform texture.