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3. Elements and Compounds Elements are materials made up of one type of atom only. Hydrogen molecule contains two hydrogen atoms bonded together, so the formula is H2. The water molecule contains two hydrogen atoms bonded to one oxygen atom, so the formula is H2O. It follows that compounds contain two or more types of atom.

4. Compounds: Water  + + Compounds are produced when elements combine. For example, water is produced in the following reaction. Two water molecules react with one oxygen molecule to give water. Word Equation Hydrogen + Oxygen  Water

5. Compounds – not mixtures The atoms in compounds are NOT mixed together. A mixture of hydrogen and oxygen would look like: +  HYDROGEN Flammable gas. OXYGEN Gas in which many substances burn. WATER Liquid that extinguishes most fires. They become bonded together during a chemical reaction. Because of this compounds have properties that are very different to the elements that they are made from.

6. Compounds – not mixtures carbon + oxygen  carbon dioxide Black solid used as barbecue fuel Gas in which many substances burn Gas used in fizzy drinks and fire extinguishers

7. It is easy to name simple compounds of metals and non-metals. Write down the name of the metal Write down the name of the non-metal but change the ending to “ide.” • magnesium • oxide • 1) magnesium 2) oxygen = • sodium • chloride • 1) sodium 2) chlorine = Element 1 Element 2 Name of compound copper bromine silver sulphur calcium oxygen Naming Simple compounds. copper bromide silver sulphide calcium oxide

8. Name the compound formed from these elements Element 1 Element 2 Name of compound iron sulphur magnesium nitrogen sodium chlorine tin oxygen aluminium bromine nickel iodine zinc sulphur lithium nitrogen Naming Simple compounds. iron sulphide magnesium nitride sodium chloride tin oxide aluminium bromide nickel iodide zinc sulphide lithium nitride

9. Many compounds contain more than two elements. Naming them can get complicated but for those containing two elements plus oxygen the name ending usually changes to –ate. Element 1 Element 2 Element 3 Name of compound nickel sulphur oxygen nickel sulphate magnesium nitrogen oxygen magnesium nitrate sodium nitrogen oxygen copper sulphur oxygen aluminium bromine oxygen Naming more complicated Compounds sodium nitrate copper sulphate aluminium bromate

10. Compounds are very different to the elements from which they are made but there is another way in which compounds are different to mixtures. In a mixture you can add any amount of the ingredients. H Mg O Na Cl O C O O H The composition of compounds. • Compounds always contain a definite amount of each element. They have a fixed composition. • This is not really surprising as looking at the word equations you will have seen they always have a definite number of element atoms joined together.

11. This means that every compound can have a formula that tells us how many of each type of atom are present. We include small slightly dropped numbers if there are more of one atom than the other. Carbon dioxide Water One oxygen atom One carbon atom Two oxygen atoms Two hydrogen atoms Formula H2O H FormulaCO2 O C O O H The formula of compounds

12. What is the formulae of each of the compounds shown? (As with names, put the metal first.) Activity 1. Titanium oxide O Ti O ? titanium atom Formula ? oxygen atoms 2. Lithium Oxide 3. Aluminium chloride O Cl Al Cl Li ? lithium atoms Li Cl ? aluminium atom Formula ? Formula ? oxygen atom ? chlorine atoms The formula of compounds 1 titanium atom Formula TiO2 2 oxygen atoms 2 lithium atoms 1 aluminium atom Formula Li2O 1 oxygen atom Formula AlCl3 3 chlorine atoms

13. What is the formulae of each of the compounds shown? Activity Silicon chloride ? silicon atom ? chlorine atoms Formula The formula of compounds Cl Cl Si Cl 1 silicon atom Cl 4 chlorine atoms Formula SiCl4 Manganese oxide Aluminium oxide O O O O Mn O Al Al 1 manganese atom ? manganese atom ? aluminium atom 2 aluminium atom Formula Formula MnO2 Formula Al2O3 Formula 2 oxygen atoms ? oxygen atoms ? oxygen atoms 3 oxygen atoms

14. Word equations can be used to describe any chemical change. (i.e. any process where the atoms become joined (bonded) in different ways). The steps are: Write down the name of the reactant(s) linking them with a + sign if there is more than one. Write down an arrow Write down the names of the products linking them with a + sign if there is more than one Word Equations

15. Write out word equations for this reaction Lead reacts with oxygen to form lead oxide Activity Lead Lead oxide Word Equations • Lead + oxygen  lead oxide Why is lead oxide so different to both lead and oxygen? • It hasn’t just mixed. • It has reacted and atoms are joined differently.

16. Write out word equations for the following reactions. Limestone (calcium carbonate) is heated to make calcium oxide and carbon dioxide. Magnesium reacts with hydrochloric acid to make magnesium chloride and hydrogen. Methane is burnt to make carbon dioxide and water. Activity Word Equations calcium carbonate  calcium oxide +carbon dioxide magnesium + hydrochloric acid  magnesium chloride + hydrogen methane + oxygen  carbon dioxide + water

17. Mixtures are, as the name indicates, mixed rather than reacted together. This means that, unlike compounds: 1 They do not have to have any particular proportions of the various ingredients. 2 Their properties are often “an average” of the properties of their ingredients. (eg. a mixture of a black and white powder is grey!) sea water: a mixture of salts and water Mixtures 3 They are mixed, not bonded, and so are usually not too hard to separate back into their ingredients. (For example, it is easy to get salt from sea water.)

19. Separating Mixtures Immiscible liquids Immiscible means “doesn’t mix” and so we are talking about “mixtures” like water with cooking oil or water with petrol. On a small scale you can simply remove the top layer using a pipette.  oil oil water water

20. Separating Mixtures Miscible liquids Miscible means “does mix” and so we are talking about mixtures like water and alcohol or petrol with kerosine. These are separated by boiling them as it is unlikely that they will boil at exactly the same temperature. In order to “get back” the liquids we use a condenser. This is a tube that has cold water circulating through the outside. It cools down vapours and condenses them back to a liquid. Substances with low boiling points collect first, while those with higher boiling points collect later.

21. Miscible liquids Distillation Equipment thermometer condenser water in water out electric heater collection beaker

22. Separations How would you get this? filter evaporate distil pipette distil

23. Separation Experiment John has been given a mixture of salt, sand and water. He needs to separate them but cannot remember how. Can you help him? Write an experimental plan for John to follow so that he can have the sand, salt and water in separate containers. Make sure you start off by telling him what equipment he will need. Then he will need a step by step plan that is easy to follow.

24. Summary activities

25. 1. Which of these is a compound? bromine copper carbon dioxide uranium

26. Which of these best describes a compound? Two or more atoms bonded together. Two or more elements mixed together. Two or elements bonded together. Two or more types of molecule mixed together.

27. Which of these could best describe compounds? Substances that: are similar to the elements that they are made from. can be formed when elements react together. can be formed when elements decompose into two or more new substances. substances with symbols in the Periodic Table.

28. What would be the name of a compound formed from sulphur, oxygen and zinc? sulphur zincide sulphur zincate zinc sulphide zinc sulphate

29. What would be the formula of a compound containing two aluminium atoms for every three sulphur atoms? A. Al2S3 B. Al3S2 C. Al2S3 D. Al3S2

30. How would you separate a mixture of water and alcohol. (Two miscible liquids) filtering chromatography evaporation distillation

31. What is the main technique you would use when separating a mixture of salt and sand? filtering chromatography evaporation distillation

32. Use the chromatogram to decide which dyes are in the ink. A B C D Ink