A Chemistry Dictionary for Students

Helping kids to understand Chemistry

 

 



Chemistry term Chemistry definitions
acid A substance that tastes sour, dissolves metals, neutralises bases and turns blue litmus red. Acids produce hydrogen ions in water.
acidity A measure of the amount of acid in a solution.
activity series of metals A list of metals arranged in decreasing order of chemical reactivity. Very active metals react with water. Active metals react with acids. Least reactive metals do not react with acids. 
alloy A mixture of a metal with one or more other elements. eg. steel (iron & carbon), solder (lead & tin), bronze (copper & tin) and brass (copper & zinc) 
amorphous A solid that has no definite shape or form because the particles are arranged randomly. eg. glass, flour, soot 
array An ordered arrangement 
atom The smallest particle or building block of an element. Initially atoms were thought to be indivisible.
atomic mass The mass of  an atom relative to the Carbon-12 atom which is exactly 12.  The atomic mass of an element depends upon the average mass of its isotopes. 
atomic number The number of protons in the atoms of a particular element. Each element has its own atomic number. 
base A substance that tastes bitter, dissolves fats, neutralises acids and turns red litmus blue. Bases produce hydroxide ions in water.
basicity A measure of the amount of base in a solution. 
binary compound  A compound that is composed of two elements
brittle The breakage into fragments when a force is applied.
centrifuging A method of separating suspensions or emulsions by rapid spinning. 
chemical bond The electrostatic attraction between particles (atoms, ions and molecules) that holds them together. There are three types of bonds the covalent bond, the ionic bond and the metallic bond. All bonds involve the outer or valence electrons. 
chemical change A change from one form to another which results in the production of at least one new substance. i.e. a chemical reaction. Chemical changes are generally difficult to reverse. They are indicated by a permanent colour change, the production of a gas, precipitate or light.
chemical property A property that describes the behaviour of a substance as it changes into other substances. ie. a new substance is formed. 
chemical reduction The chemical separation of a compound resulting in the production of a metal.  
chemical separation A means of separating compounds into simpler substances based upon the chemical properties of that compound. At least one new substance is formed. eg. electrolysis, chemical reduction, heating. 
compound A pure substance made up of two or more elements that are chemically joined (chemical bonds). Compounds can be broken down into simpler substances by chemical means.
compound A pure substance made up of two or more elements that are joined together by chemical bonds. Compounds can be broken down into simpler substances by chemical separation. ie. electrolysis, chemical reduction producing metals and by thermal decomposition. 
concentrated A solution containing a large amount of solute  
condensation A change in state from gas to liquid. The gaseous particles slow down enough for the attractive forces between the particles to bring them close together. 
covalent bond A chemical bond joining two non-metal atoms. eg. H2O. Valence electrons are shared between the atoms. The attraction is between the shared electrons and the positive nuclei between the atoms. 
crystal A solid that has a definite geometric shape or pattern because the particles are arranged in an orderly manner. eg. table salt is cubic. 
crystal lattice  A solid in which the particles (atoms, ions or molecules) are arranged in a orderly pattern. 
decanting The separation of an insoluble solid from a liquid by carefully pouring off the liquid leaving the solid sediment behind. 
diffusion The random movement of particles in the liquid or gaseous state form an area of high concentration to an area of low concentration. 
dilute A solution containing a small amount of solute
dissolving The separation of the particles of a solid by a liquid.  
distillation A method of separation substances based upon differences in boiling points. It involves the evaporation and condensation of one or more liquids. 
ductile Able to be drawn out into a thin wire.
electrical conductivity A measure of the amount of electricity that can flow through a substance.
electrolysis The chemical separation of a compound into simpler substances using electricity . electro = electricity and lysis = to split.
electron A negatively charged sub-atomic particle which orbits the nucleus of an atom. The outer electrons are involved in chemical reactions and form chemical bonds with other atoms.
element A pure substance composed of the same type of atoms. It cannot be broken down into simpler substances by chemical means. 
element A pure substance composed of atoms with the same number of protons. Elements may be composed of various isotopes.  eg. The element carbon is composed of 98.9% of carbon-12, 1.1 % of carbon-13 and a trace amount of carbon-14. All isotopes of carbon have 6 protons.
emulsion A mixture containing two liquids that cannot mix, one being dispersed throughout the another as very small droplets. eg. oil, water and detergent. The appearance is opaque(cloudy) as light is scattered.
evaporation The change from liquid to gas. The liquid particles escape the attractive forces holding them closely together. 
filtrate The liquid that passes through the filter paper. 
filtration A method of separating an insoluble solid from a liquid. The solid residue remains in the filter paper while the liquid filtrate passes through. 
fusion or melting The change from a solid to a liquid. The solid particles overcome the attractive forces holding them in fixed positions and start to move over one another. 
gas A state of matter in which the particles are far apart and are rapidly moving past one another. In this state matter has a variable shape and a variable volume. ie. the shape and volume are determined by the container it fills. 
impure substance or mixture A substance consisting of two or more particles that can be separated by physical means. eg. evaporation. Its properties are dependent upon the composition of the mixture. eg. The concentration of a copper sulfate solution determines it colour. 
indicator A chemical which changes colour in acidic or basic solution. 
insoluble The inability of a solid to dissolve in a liquid. eg. sand in sea water. 
ionic bond A chemical bond joining a metal atom with a non-metal atom. eg. sodium chloride. Valence electrons are transferred between the atoms producing charged particles or ions. The attraction is between the positive metal ions and the negative non-metal ions. 
isotope Atoms of a particular element that differ in their atomic mass due to a different number of neutrons their nucleus.  
lattice An ordered  geometrical arrangement consisting of fixed points in which particles (atoms, ions or molecules) vibrate.  
liquid A state of matter in which the particles are close together and are moving over one another. In this state matter has a variable shape and a fixed volume.
litmus A chemical indicator which is red in acidic solution and blue in basic solution. 
lustre The shine produced by metals reflecting light.
malleable Able to be hammered into thin sheets.
matter Anything that has mass and takes up space. (ie. has volume)
metal An element that has lustre, is a good electrical and thermal conductor and is malleable and ductile
metallic bond A chemical bond joining metal atoms. eg. magnesium. Valence electrons are mobile and move between the atoms creating positive metallic ions. The attraction is between the positive metallic ions and the negatively charged mobile electrons. 
molecule A particle consisting of two or more atoms chemically joined together.
molecule The smallest particle of a substance capable of independent existence. Monatomic molecules exist by themselves. The atoms in diatomic and polyatomic molecules are joined together by covalent bonds. eg. H2, H2O 
neutral A solution which is neither acidic or basic. 
neutron A sub-atomic particle found in the nucleus of an atom which is neutral in charge. Neutrons are thought to help stabilise the nucleus.  
non-metal An element that is dull, is a poor electrical and thermal conductor and that is brittle.
nuclear model  The atom is composed of a positively charged nucleus containing most of the atoms mass and is surrounded by a large amount of empty space which is orbited by negatively charged electrons. 
nucleus The central region of an atom which is positive in charge and contains most of the atom’s mass. It is composed of protons and neutrons. 
opaque The inability of light to pass through a substance. Light is scattered. 
paper chromatography A method of separating substances as they are carried by a solvent as it moves through paper.
particle The smallest unit of matter that has its own properties.  
particle theory of matter All matter is composed of individual particles (atoms, ions, molecules) which are attracted to one another and are constantly moving in all physical states (solids, liquids, gases)  
pH scale A scale which measures the acidic or basic strength of a solution.  pH < 7 is acidic (6 is a weak acid and 1 is a strong acid), pH = 7 is neutral, pH > 7 is basic (8 is a weak base and 14 is a strong base).  
physical change A change from one physical state to another. eg. evaporation, condensation, sublimation, solidification, fusion or melting. 
physical change A change in appearance from one form to another which does not result in the production of a new substance. eg. a change in physical state (solid, liquid or gas) or a substance being dissolved. Physical changes are easy to reverse.  
physical property A property that can be observed or measured without altering the substance. ie. no new substance is formed. eg. colour, physical state, density, crystal shape as a solid, melting and boiling point.
physical separation A means of separating impure substances into pure substances based upon the physical properties of the mixture. No new substances are formed. eg. filtration, evaporation, dissolving  
property Anything about matter which helps identify it.
proton A sub-atomic particle found in the nucleus of an atom which is positive in charge. The proton determines the properties of an atom. The atoms of each element have the same number of protons. 
pure substance A substance consisting of only one type of particle. It cannot be separated into simpler substances by physical means. eg. filtration. Its properties are unique for that particular substance and are constant. ie. do not change. eg. melting and boiling point of water. 
radioactive decay The ‘fission’ or splitting of a nucleus into smaller nuclei releasing energy as radiation.
radio-isotope An isotope of a particular element that undergoes radioactive decay.
residue The solid left in the filter paper after the liquid has passed through.
saturated A solution that contains all the solute it can dissolve. Excess solute remains undissolved at the bottom of the solution. 
semi-metal or metalloid An element that has the some of the properties of a metal and some of the properties of a non-metal. eg. silicon is a semi electrical conductor (metallic property) and is brittle (a non-metallic property) 
solid A state of matter in which the particles are close together vibrating in fixed positions. In this state matter has a fixed shape and a fixed volume. 
solidification A change in state from liquid to a solid. The particles slow down sufficiently for the attractive forces between them to be strong enough to hold the particles in fixed positions. 
solubility The extent in which a solute dissolves in a solvent at a particular temperature. 
solubility A measure of the amount of solute that can dissolve in a solvent
soluble The ability of a solid to dissolve in a liquid. eg. salt in water. 
solute The substance dissolved by a solvent
solution A mixture consisting of a solute(solid) dissolved in a solvent (liquid). The appearance is clear(transparent) as light passes straight through.  
solution A solute dissolved in a solvent. Solutions may be acidic, neutral or basic in composition. 
solvent The liquid that dissolves a solute
sub-atomic Small particles which make up the atom.  ie. the proton, the neutron and the electron.  
sublimation A change in state from solid to gas without the formation of a liquid. eg. dry ice (solid carbon dioxide) 
super saturated A solution that contains excess dissolved solute above its saturation level. The excess solute eventually crystallises out. 
suspension A mixture consisting of small particles of solid dispersed throughout a liquid. The appearance is cloudy(opaque) as light is scattered. 
temperature A measure of the average speed or kinetic energy of the particles in a substance. 
thermal conductivity A measure of the amount of heat that can flow through a substance.
thermal decomposition The chemical separation of a compound into simpler substances using heat. 
transparent The ability of light to clearly pass through a substance without being scattered. 

 

Molar Mass
 

Formula Calculator