Chemistry New

Activation energy

The minimum amount of energy which colliding molecules must have before they can react together.

Addition polymer

A polymer made by the combining together of small unsaturated molecules of the same

Addition reaction

A reaction in which the double or triple bond of an unsaturated compound opens up and other atoms add on to the molecule. Addition reactions are characteristic of the alkenes and alkynes.

Alkali metals

The elements of Group 1 of the Periodic Table.

Allotropes

Allotropes are different physical forms of the same element (and are due to different arrangements of the atoms of the element). The allotropes of carbon are diamond, graphite and charcoal.

Aliphatic compound

Compound whose molecule contain only chains of carbon atoms.

Alkali

A base that is soluble in water.

Alkaline earth metals

The elements of Group 2 of the Periodic Table.

Alkanes

Hydrocarbons in which there are only single bonds between carbon atoms.

Alkenes

Hydrocarbons in which there is a double bond between two carbon atoms.

Alkynes

Hydrocarbons in which there is a triple bond between two carbon atoms.

Alloy

A mixture of metals.

Amphoteric oxide

An oxide which shows both acidic and basic properties (i.e., it can react with both alkalis and acids).

Amphoteric substance

One which can act both as an acid and as a base.

Anion

The ion which is attracted to the anode/Negative ions

Anode

The positive electrode in electrolysis.

Anodising

Anodising is a process in which the normal thin layer of oxide on the surface of aluminium is artificially thickened to give it added protection from corrosion. It is done by making aluminium the anode in an electrolysis cell in which dilute sulphuric is electrolysed.

Aromatic compounds

Compounds whose molecules contain a 6

Atomic number

The atomic number corresponds to the number of protons in the nucleus of an atom of that element. It also corresponds to the number of electrons in the neutral atom.

Atomic radius

Half the distance between the nuclei of two atoms of the same element in a covalent bond

Aufbau principle

Electrons occupy the lowest available energy level.

Autocatalysis

The catalysis of a reaction by one of the products of that reaction.

Avogadro constant

The number of carbon atoms in exactly 12 grams of the carbon

Avogadro's law

Equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules.

Biochemical oxygen demand (BOD)

A measure of the amount of organic pollution in water. It is defined as the amount of dissolved oxygen consumed by biochemical action, when a sample of water is kept in the dark at 20° C for 5 days.

Boyle's law

For a fixed mass of gas is kept at constant temperature, the volume is inversely proportional to the pressure.

Brønsted acid

A substance (molecule or ion) that can donate protons.

Brønsted base

A substance that can accept protons.

Carbonate (Anion Test)

Dilute HCl

Fizzes and the limewater turns milky, white precipitate forms after magnesium carbonate

Catalysis

The process of changing the rate of a chemical reaction by the action of a catalyst.

Catalyst

A substance that alters the rate of a chemical reaction but which is not used up during the reaction, and which is chemically unchanged at the end of it.

Catalyst poison

A substance which destroys the activity of a catalyst.

Cathode

The negative electrode in electrolysis

Cation

The ion which is attracted to the cathode/Positive ions

Charles' law

For a fixed mass of gas kept at constant pressure, the volume is directly proportional to the absolute temperature.

Chloride (Anion Test)

Silver Nitrate (AgNO3)

White precipitate is formed, soluble in dilute ammonia

Concentration

The amount of a substance per unit volume of solution.

Condensation reaction

A reaction in which two compounds combine together and eliminate water (or other small molecule such as HCl).

Conjugate acid

The substance formed when a Brønsted base has accepted a proton.

Conjugate base

The substance formed when a Brønsted acid has lost a proton.

Conjugate pair

A pair of substances that differ by a proton.

Co

product

Covalent bond

One or more shared pairs of electrons, each of the bonded atoms contributing one electron towards the shared pair. Covalent bonds may be either pure or polar.

Cracking

The breaking down of long

D

block element

Dehydration

The removal of water, or the elements of water, from a compound or compounds.

Deionised water

Water in which ions that were present in it have been removed by passing the water through an ion exchanger, which replaces any positive ions by H+ ions and any negative ions by OH

Dipole

dipole forces

Dissociation constant of an acid (Ka) (or a base (Kb)

A measure of the extent to which the acid (or base) dissociates (ionises) in solution, and which is given by Ka = . It is only applicable to weak acids and bases.

Distilled water

Water which has been boiled and the steam from it condensed; it therefore contains no dissolved solids.

Double bond

Two shared pairs of electrons.

Effluent

Liquid industrial waste

Electrochemical series

A list of elements in decreasing order of ease with which they lose electrons.

Electrodes

The conductors by which the current enters and leaves the solution in electrolysis. The positive electrode is called the anode and the negative electrode is the cathode.

Electrolysis

The process in which an electrolyte is decomposed by passing a current through it.

Electrolyte

A compound which in liquid state conducts electricity and is decomposed in doing so.

Electronegativity

A measure of the attraction of an atom of an element for the shared pair of electrons in a covalent bond.

Electroplating

The process of covering one metal (usually a cheap and/or plentiful one) with a thin layer of a more expensive one, to provide protection and/or better appearance.

Electropositive

Describes elements that readily lose electrons to form positive ions.

Empirical formula

The formula of a compound that shows only the ratio in which the different types of atom are present in the molecule.

Endothermic reaction

A reaction in which heat is taken in or "used up".

Energy level

A measure of the amount of energy possessed by an electron when it is in an atom.

Equilibrium

A balanced state of constant change in a system. Chemical equilibrium refers to the state in a reversible reaction when the rate of the forward reaction is equal to the rate of the backwards reaction.

Equilibrium constant, Kc

For a reversible system, a constant that tells how far the reaction has gone to the right

Esterification

A reaction in which an acid and alcohol react together, to form an ester and water.

Eutrophication

The enrichment of natural waters by nutrients (nitrates and phosphates in particular); it causes the very rapid growth of algae which, when they die and decay, consume large amounts of oxygen. The water is then depleted of oxygen, and fish and aquatic life die.

Excited state

The state of an atom when one or more of its electrons have been promoted to higher energy levels.

Exothermic reaction

A reaction in which heat is liberated.

Feedstock

Raw materials needed for a chemical manufacturing process.

Fixation of nitrogen

The process in which atmospheric nitrogen is made to combine with other elements to form useful compounds.

Flocculation

The process in which small particles in water are made to coagulate (clump together) and form a precipitate. It is done by adding a FLOCCULATING AGENT such as aluminium sulphate or iron (III) sulphate.

Fractional distillation (or fractionation)

The process in which a mixture of liquids is separated into components or fractions of different boiling points (or different boiling points ranges).

Functional group

A group of atoms on which the characteristic properties of a particular compound depend.

Gay Lussac's law

In a reaction between gases, the volumes of the reacting gases and the volumes of the products, if gaseous, are in the ratio of small whole numbers (at the same temperature and pressure).

General gas law

This is a combination of Boyle's and Charles' laws, and is most simply expressed as =

Ground state

The state of an atom when all of its electrons are in their lowest available energy levels.

Halogens

The elements of Group 7 of the Periodic Table (i.e., fluorine, chlorine, bromine and iodine).

Halides

Compounds which contain a halogen and one other element (e.g., fluorides, chlorides, bromides and iodides).

Hard water

Hard water is water which will not readily form lather with soap due to the presence of dissolved calcium or magnesium salts in the water.

Heat of combustion

The heat change which occurs when one mole of a substance is burnt in an excess of oxygen.

Heat of formation

The heat change which occurs when one mole of a compound is formed from its elements in their standard states.

Heat of reaction

The heat change which occurs when a reaction takes place according to a given chemical equation.

Heat of neutralisation

The heat change that occurs when one mole of H+ ions from an acid reacts with one mole of OH" ions from an alkali.

Heisenberg's uncertainty principle

It is not possible to ascertain both the position and the momentum of an electron in an atom simultaneously.

Hess' law

The heat change for a given reaction depends only on the initial and the final states of the system, and is independent of the path followed.

Heterogeneous catalysis

A system in which there is a distinct boundary between the catalyst and the reactants.

Heterolytic fission

The breaking of a covalent bond so that one atom retains the two shared electrons and the other atom retains none. Ions are thus formed.

Homologous series

A series of compounds, all members of which contain the same functional group, and successive members differ by CH2.

Homolytic fission

The breaking of a covalent bond so that each atom retains one of the shared electrons, forming two free radicals (or free atoms).

Homogenous catalysis

A system by which both the catalyst and the reactants are in the same phase or state.

Hund's rule

When two or more orbitals of equal energy are available to electrons, the electrons occupy them single before filling them in pairs.

Hydrolysis

The decomposition of a compound by means of water (or the OH ion), the water also being decomposed in the reaction.

Hydrocarbons

Compounds containing hydrogen and carbon only. Hydrogenation Action The reaction in which hydrogen adds on across a double or triple bond.

Hydration

A reaction in which a compound combines with water.

Hydrogen bond

The electrical attraction between the slightly positive hydrogen atoms of one molecule and a slightly negative atoms in another molecule.

Hydrogen

carbonate (Anion Test)