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1 S1 Science Elements, compounds and mixtures Revision Sheet Elements Everything is made up of tiny particles called atoms. An element is a substance made of only one type of atom o Each element can be identified by a unique symbol, found in the Periodic table o For example, carbon is represented by C o Examples of everyday elements include o Oxygen needed to keep all living things alive o Copper metal used in plumbing and electric cables o Helium- used in to inflate balloons The Periodic Table The Periodic Table contains all known elements o The elements are organised in the table by their atomic number and chemical properties o The elements are organised into rows called periods and columns called groups o Metal elements are found on the left hand side and non-metals are found on the right of the bold black zig-zag line Hydrogen is the exception to this rule of metal and non-metals vary. Property Metals Non-metals Appearance shiny Dull / not shiny Electrical conductivity Uses linked to their properties Conduct electricity Wires Do not conduct electricity Cooking equipment

2 There are different groups in the periodic table which have unique chemical properties o Three of these groups are summarised below Group 1- Alkali metals o are soft metals o very reactive. Elements become more reactive as you go down the group. o Lithium in batteries o Potassium in fertilisers Group 7- Halogens o non-metal o poisonous gases o colourful become darker as you move down the group o harmful elements become less harmful as you go down the group. o chlorine used to clean swimming pools o fluorine is added to toothpaste to strengthen enamel of your teeth Group 8- Noble Gases o non-metal o very unreactive gases o helium in balloons o neon in advertising signs Comparing elements, mixtures and compounds Elements are made up of only one type of atom Mixtures are made up of more than one type of atom which are not chemically bonded and so are easily separated Compounds are made up of more than one type of atom which are chemically bonded and so are not easily separated Diagram to represent elements, mixtures and compounds Element Mixture Compound

3 Naming Elements from Compounds Compounds have a chemical formula which is based on the symbols of the elements which it is made from The chemical formula of a compound tell you what elements are present within it based on their symbol from the periodic table o E.g CO 2 has the symbols C and O showing the compound contains carbon and oxygen o E.g NaCl has the symbols Na and Cl showing the compound contains sodium and chlorine Properties of Compounds and elements Different elements have different chemical properties. For example :- o Sodium (Na) is very reactive in water and chlorine (Cl) is poisonous gas o Sodium and chlorine form the compound sodium chloride NaCl which is a white soluble solid and is unreactive in water. Separating mixtures There are different techniques that can be used to separate a mixture Filtration can be used to separate an insoluble solid substance from a solution o filtration is used during water purification Evaporation can be used to separate a soluble solid from a solution o a solid is soluble when it dissolves in a solvent o a solid is insoluble when it does not dissolve in a solvent

4 Chromatography is used to separate mixtures made up of different colours such as dyes and inks o Chromatography is a method used in forensics Distillation is used to separate liquids with different boiling points. o A liquid is heated and different substances are evaporated off and collected Thermometer Water out Condenser Flask Heat Solution Water in Beaker Distillate Breaking compounds The elements in a compound are chemically joined together. This means that energy is required to separate the elements. A compound can be broken down into its elements using a process called electrolysis Battery Copper chloride solution Chlorine gas Positive electrode Copper metal Negative electrode

5 Solubility A solid is soluble when it can dissolve in a liquid called a solvent. A solid is insoluble when it cannot dissolve in a liquid called a solvent. The solubility of a substance can be affected by factors such as:- o temperature Increasing temperature increases solubility o particle size Decreasing particle size increases solubility o volume of solvent the greater the volume of solvent, the greater the solubility of a solid o type of solvent