Pure and Mixed Substances A pure substance contains only one substance and is either an element or a compound. They cannot be broken down any further. They have the same composition and the same properties. A Mixture has several different substances mixed together. They may have different properties as the proportions of each substance may vary.

Chromatography: Questions Pg 74 1) What is chromatography? 2) What is they type of chromatography used in industry? 3) What is a recent event that would have required the use of chromatography? 4) Name some uses of gas chromatography. 5) In your experiment you noticed that some colours moved faster then others, Why?

Atoms Atoms are the building blocks of all matter.

Molecules Atoms are not usually found on their own. Two or more atoms joined together is called a MOLECULE They are held together by a strong forced called a CHEMICAL BOND.

Elements A piece of copper is made up of millions of tiny copper atoms. They are all the same. Similarly, lead is made of lead atoms, but these are different from the copper atoms. Pure substances like copper and lead whose atoms are all the same are called ELEMENTS.

The first 20 elements. Harry He like beer, but could not open flagons never. Naughty Margaret always sits perched staring cluelessly around kitchen chaos

Rules for writing element symbols. All elements have their own symbol The first letter must be a capital If it has a second letter it must be lower case. E.g. Carbon = C and Calcium = Ca

Atoms, Molecules and Elements Atoms are the _____ blocks of all _____. Two or more atoms joined together is called a _______. E.g. a water molecule is made of two _______ atoms linked to one ______ atom held together by a ________ bond. An element is a ____ substance made up of only ___ type of ____. E.g. a piece of copper is made of millions of tiny copper _____ that are all the _____.

Elements Each element is represented by a symbol. The first letter is a capital If the element has a 2nd letter it is in the lower case For example: Carbon = C Calcium = Ca Some names have been changed E.g. Sodium used to be called Natrium Its symbol is Na.

Compounds and counting their atoms A compound is a substance made up of 2 or more DIFFERENT kinds of atoms. The chemical formula of a compound tells you which elements are in the compound. E.g. H2O: has 2 hydrogen atoms and 1 Oxygen. If there is more then 1 atom we use a small subscript number.

Questions – Count the atoms in the chemical formulae and say whether it is an element or compound. 1) He 2) H2 3) CO2 4) NH3 5) O3 6) CH4 7) FeO 8) Cl2 9) C6H12O6 10) H2SO4 11) MgHCO3 12) C2H6OH 13) Describe the difference between an atom and an element. 14) Describe the difference between an element and a compound.

Chemical change In a chemical reaction a change happens to the substances in it and a new substance or substances are made. It is usually irreversable The substances used (reactants) behave differently to the substances which are made (products) We can’t get more out of it than we put into it, we can only get a rearrangement of the particles that make up the reactants.

Chemical change How do we know if a chemical reaction has taken place and a chemical change has happened? The reactants might bubble The reactants might get hot The reactants might change colour The reactants might turn from a solid to a gas The reactants might burst into flame.