chemistry revision

atomic structure 

atoms - tiny particles of matter which all substances are made up of. all of its mass is concentrated in the nucleus and is determined by the mass number. they are very small with a radius of about 1x10^-10 meters.

elements - substances made up entirely of atoms that contain the same number of protons and cannot be split up any further. there is a limited number of elements and they can all be found on the periodic table.

compounds  - a compund is a pure substance made up of two or more elements that are chemically combined and unable to be seperated by physical means. the propertaies of these compounds are usually quite different to the properties of the elements that formed them. elements take place in chemical reactions in which new substances called compounds are ussualy formed. these chemical reactions often involve an energy change as the atoms combine together in fixed ratios to form full outer shells. there are two types of compound. they are:

ionic compounds - metal and non metal elements that have been joined together as ions, ionically. in the formulae the metal element is always wtieen first and the non metal is written second with the ending ide ( or ate in the prescence of oxygen )

covalent compounds - two non-metaks bonded together covalently and use prefixes such as 'mono'  in  'monoxide'.

equations - equations show the processes of different chemical reactions by showing the products and the reactants in one line. there is an arrow inbetween the products and reactants and the name of any catalysts can be written above the arrow. there are many types of equation, they are:

symbol equations - symbol equations use the formulae of reactantts and products to show what happens in  a chemical reaction. they must be balanced. 

half equations - half equations are used to show us what happens to the electrons in reactions where they are gained and lost. they are called this because each reaction has 2 and each equation only showws us half of what is happening.

ionic equations - ionic equations are used to show us what happens to the ions in reactions and they are used to help simplify complicated reactions by using H⁺ to represent the acids and OH^- to represent the alkalis.

during chemical reactions new substances are made but the same atoms are always present afterwards, they are just joined up in different ways as atoms cannot be either created or destroyed, meaning that the total mass of the reactants is equal to the total mass of the products. this is known as the law of conservation of mass.

mixtures - two or more elements/compounds that are not chemically combined together and that can be separated

seperation techniques for mixtures:

filtration - a method used to seperate an undisolved solid from a mixture with a liquid ( e.g sand and water ). it requires filter paper, a funnel and a beaker…