Chemistry Definitions A-F

Chemistry Definitions  of words beginning with the letters A to F.

A

Abrasion     Rocks bang into each other and become smaller and more rounded.

Acid rain     All rainfall is slightly acidic because of the dissolved carbon dioxide. The term acid rain refers to rain that is extra acidic because of large amounts of dissolved gases such as nitrogen oxides and sulphur oxides. These can make nitric acid and sulfuric acid as well as many others.

Addition reaction     A substance is reacted with an alkene to form a compound with a single bond between the two formerly double bonded carbon atoms. An example is the decolourisation of bromine.

Addition polymerisation     One long single molecule is made from many short chain monomers. All the starting material is incorporated in the final polymer. An addition reaction taks place each time the chain is extended.

Air     The mixture of gases which we breathe! Most of the air (almost 4/5) is nitrogen with oxygen making up 1/5 and small amounts of argon (1%) and other gases in even smaller amounts. Carbon dioxide is only present in very small quantities. Water vapour is present in varying amounts depending on where you are in the world.

Air pollution     Substances that have been released into the air that are not natural. In the past, people have not been very concerned about waste being put into the atmosphere. Many thought that a tall chimney would remove the problem. Nowadays we are much more careful and take more care to dispose of problem gases, smoke and dusts in a more responsible way.

Alkane     A hydrocarbon that has only single bonds. It is a saturated hydrocarbon.

Alloy     A mixture of different metals. Bronze, brass, duralumin are some typical examples of alloys.

Atom     The smallest particle that can be recognised as being an element. If you break an atom into its smaller pieces (protons, neutrons and electrons) you can no longer identify a particular element.

B

Balanced chemical equation     If ever you write a chemical equation using symbols it MUST be balanced. That means that there must be the same number of each kind of atom on either side of the equation.

Basalt     An igneous rock which cooled quickly from magma. The rapid cooling (perhaps under water) caused it to have small crystals.

Base     A substance that will neutralise an acid is called a base. When an acid reacts with a base, a salt and water is formed. If a base is soluble in water, it is called an alkali.

Biological weathering     Rocks can be broken down in many ways. Biological weathering is the breakdown of rocks by biological action. A good example is where the roots of plants growing in cracks in rocks causes them to split.. 

Boiling     When boiling, a liquid is evaporating as fast as it can. If you look at a boiling liquid (careful!) you will see that it is forming bubbles in the body of the liquid. 

Boiling point     This is the maximum temperature a liquid can achieve. For water, the boiling point is 100^oC (at standard atmospheric pressure). Pure liquids have a single steady boiling point.

Boiling point range     In the fractional distillation of crude oil, the substances are collected in groups (fractions) according to their boiling point range.

Bonds     There are three main kinds of bonds at GCSE level.

An ionic bond holds two ions (of opposite charge) together by electrostatic attraction. Ionic bonding occurs between a metal and a non-metal. A good example is sodium chloride.

A covalent bond uses a shared pair of electrons to hold two atoms together. This usually occurs between two non-metal atoms. There are covalent bonds between the atoms in ammonia.

A metallic bond is formed by a delocalised sea of electrons surrounding the very tightly packed metal atoms.

Brine     A solution of sodium chloride (common salt) in water is called brine. 

Bubble     A bubble contains a gas. Bubbles in a liquid when it is boiling contain the vapour of that liquid. Bubbles of gas can be formed during a chemical reaction. 

C

Calx     It was believed to be an ash-like substance which is left when the phlogiston leaves a metal. Although we now believe that metals form metal oxides when they burn, we no longer believe the phlogiston theory. 

Carbon dioxide     This is a slightly acidic gas that is formed when carbon burns in air (or oxygen). It does not support combustion and so a burning splint will be extinguished by the gas. However, this is NOT the test for carbon dioxide. To test for the gas, bubble it into limewater. A milky white precipitate shows that the gas is carbon dioxide. 

Carbon dioxide is produced during respiration (this is true whether the respiration is by animals, plants or even anaerobic respiration of yeast during fermentation). 

Carbon monoxide     This has the formula CO and is a possible product if a fuel burns in a poor supply of air. It is a toxic gas. It can be removed from the exhaust gases of cars by the use of a catalytic converter. You should be able to write a word equation for its formation during a combustion reaction.

Carbon steels     Steel can contain up to 1.5% of carbon. This is much less than the 4% found in cast iron.

Cast iron     This is iron as it comes out of the blast furnace. It contains around 4% carbon and so is brittle. Some of the carbon is removed as th cast iron is converted to steel.

Catalytic converter     This is a device fitted to the exhaust pipe of a car in order to convert the harmful gases into less harmful ones. The particular gases to be removed are carbon monoxide and the nitrogen oxides.. After conversion , these become nitrogen (already 4/5 of the atmosphere) and carbon dioxide (although a pollutant since it is a greenhouse gas, the amount of carbon dioxide released in this way is very small compared to the amount emitted by burning the fuel). 

Cement     Limestone is heated to a high temperature with clay and then powdered. It is mixed with sand and water to make mortar.

Cementation     This is one of the processes of sedimentary rock formation. The water is squeezed out from the gaps between the grains of sand etc of the wet sediment. This leaves behind the mineral salts which can act as a kind of glue to hold the grains together. 

Chemical equation     (Don't confuse this with chemical formula) If you are asked for a symbol equation is must be balanced.

Chemical formula     (Don’t confuse this with chemical equation) This is the chemical code for a substance. If the substance forms molecules the formula tells us how many atoms of each element are in the molecule. 

Eg HCl contains one hydrogen and one chlorine 
C₂H₅OH contains two carbons, six hydrogens and one oxygen

If the substance does not form molecules (such as ionic solids), the formula tells us the ratio of each kind of ion. 

Eg NaCl has one sodium ion for every chloride ion 
CuCl₂ has one copper ion for every two chloride ions

Sometimes brackets can be used to make things clearer: 

CuNO_{3 2} might mean one copper, one nitrogen and thirty two oxygens but

Cu(NO₃)₂ clearly means one copper, two nitrogen and six oxygens 

Chemical reaction     A change where one or more new substances are formed. It is difficult to undo a chemical change. 

Chemical weathering     Rocks can be broken down by many effects. Chemical weathering is where this breakdown is caused by chemical action. This is often due to acidic rainfall and is made worse when the rain is made extra acidic by pollution (acid rain). 

Chromatography     Literally means coloured writing, it is a technique used to separate coloured materials. You can use chromatography to separate the colours of ink (maybe black ink contains red, blue and brown dyes) or food colourings (smarties are good for this). Forensic science uses chromatography to investigate substances found at the scene of a crime and can trace DNA etc. 

Coke     Coal is heated in the absence of air (so not burned) to drive off volatile components and form coke. It is a raw material in the blast furnace as a source of carbon. 

Combustion     This is a scientific word for the burning of a fuel.

Compound     A substance containing two or more different kinds of atoms chemically joined together.

Concrete     This is formed by mixing cement, sand, stones (or crushed rock) and water. It can be poured into a hole to form a block for building foundations or into a mould to produce a variety of shapes (eg girders and railway sleepers). It can be reinforced by being poured around steel cables or mesh.

D

Data     The results and information that has been collected form an experiment 

Datalogger     A device that can be linked to a computer to record the results from an experiment automatically.

Decomposition     A reaction where one substance breaks down into two or more new substances. An example of a decomposition is heating calcium carbonate to produce calcium oxide and carbon dioxide 

Density     The mass of a body divided by its volume. Something has a high density of it is heavy but only small. Diagonal relationship The properties of lithium and magnesium are similar in many ways. The same goes for aluminium and beryllium. 

Diffusion     Particles spread out and mix. This occurs in both gases and liquids but goes faster in gases. 

Displacement reaction     Sometimes called a “reactivity series reaction” this is where a reactive metal takes the place of an unreactive one in a compound. Look at this example (zinc is more reactive than copper or you could say that zinc is higher in the reactivity series than copper): 

zinc + copper sulphate goes to make zinc sulphate + copper 

Dissolving     A solid breaks down and spreads out through a liquid. The solute (the one that gets dissolved) particles are so small that they can pass through filter paper. 

Distillation     A liquid is separated from its solution by heating it so that the liquid evaporates and then cooling the vapour so that it condenses somewhere else. 

Diamond     One of the allotropes of carbon. Allotropes have the atoms of the same element but arranged in a different way.

E

Electrical conductor     A substance that allows electricity to flow through it without any chemical change taking place.

Electrolysis     The chemical change that is brought about by passing electricity through a substance. The substance must be ionic and either molten or in aqueous solution.

Electron     An atomic particle of very small mass (1/1840 of the mass of a proton) and a charge of one minus. It is found in an atom in shells or orbits surrounding the nucleus but not part of the nucleus. 

Element     This is a substance that is composed of only one kind of atom. All the atoms in an element are the same. A chemical reaction cannot break an element into anything simpler.

Erosion     This is the transport (movement) of bits of rock after they have been broken down weathered).

Evaporation     A liquid turning into a gas. Although a liquid may evaporate (from its surface) at any temperature, it can only boil at its boiling point.

Expansion     When a substance is heated, it expands or gets bigger. Some people think (incorrectly) that it is the particles themselves that are getting bigger but this is not true. Instead, the substance expands because the particles are moving more violently.

F

Filtering (Filtration)     A method of removing an insoluble solid from a liquid. The liquid particles and any dissolved particles are small enough to fit through the holes in a filter paper. An undissolved solid has particles that are too big to do so.

Flow     Another word for move. It is often used to describe the movement of lava.

Formula (see chemical formula)

Fossil     The remains of an animal or plant that have been turned into rock and preserved. They are only found in sedimentary rocks (since the changes that produce metamorphic and igneous rocks would destroy any fossils)

Fossil record     A method of dating rocks by looking at the types of fossil that are present and matching them to samples from elsewhere. It can also help in identifying the movement of continental plates.

Fraction     A set of hydrocarbons with similar boiling points that is produced by the fractional distillation of crude oil.

Fractionating column     Used in the fractional distillation of crude oil. It is hotter at the bottom. Crude oil is heated to form a vapour which is then passed in at the bottom of the fractionating tower.

Freeze-thaw     When water turns to ice, it expands. If some water is trapped in a crack in a piece of rock, the freezing can cause more damage to the rock. If this process is repeated many times, the rock can be broken down. This is an example of physical weathering.

Freezing point     The freezing point is the temperature at which a liquid becomes solid. It is the same value as the melting point.

Freezing point depression     It can be used to identify a substance and it also shows that a liquid is not pure. It explains why salt is spread on the icy roads. Salt solution has a lower freezing point than pure water.

Fuel     A substance that can be burned to release energy. When considering energy resources, fuels are often divided into renewable and non-renewable fuels. Renewable fuels are those which can be replaced fairly quickly (such as alcohol which is formed from fermenting sugar from fast growing sugar cane).