ELEMENTS AND COMPOUNDS

1. ELEMENTS AND COMPOUNDS BUTTONS Click here; Clicking here will allow you to hear some information on the topic. Clicking here again will stop the sound. Clicking here will reveal an answer. Clicking here will move you back a page. Clicking here will reveal some information. Clicking here will take you to a periodic table, clicking here again will take you back to the previous page. Clicking here will move you to the next page. Clicking here will take you to a common ion table. Clicking here again will take you back to the page you were on previously. Jump to… Clicking here will bring you back to this page. TOPICS Jump to… …elements and compounds. Jump to… …chemical formula. Jump to… …working out the formula (two pages). Jump to… …practise questions (two pages). …exam paper questions (four pages).

2. ELEMENTS AND COMPOUNDS ELEMENTS An element is a substance that cannot be broken down into anything simpler by chemical means. Compounds are substances made of two or more different types of atoms. The atoms in a compound are chemically bonded to each other and are difficult to separate. They are the building blocks of everything you see around you. Each individual element is made up of just one type of atom, e.g. The elements iron and sulfur combine to make the compound iron sulfide. COMPOUNDS • sulfur just contains sulfur atoms; S S S S S S S S Fe Fe S S S Fe Fe Fe S S S S S S Every compound has a chemical formula which shows the number of each element making it up, e.g. iron sulfide is FeS. • whilst iron just contains iron atoms; Fe Fe S S S Fe Fe Fe S S Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe Fe

3. CHEMICAL FORMULA A shorthand way of representing a compound is by using a chemical formula. Ca (O H)2 SYMBOL FORMULA The formula to the right is the symbol formula of a compound called calcium hydroxide. Click each of the letters in this formula to see the number of atoms of each element making it up. 1 calcium atom 2 oxygen atoms 2 hydrogen atoms PICTURE FORMULA We can also show a compound using a picture formula. Click on a coloured atoms in this diagram to show how they’re linked to the symbol formula. H3 P O4 P H H H O O O O

4. WORKING OUT THE FORMULA 1 What is the formula ofiron(III) oxide? Use a common ion table to find the ions for the elements in the formula, so here we haveiron(III)(Fe3+)andoxide(O2-). Rub out the+and–charges, leaving just the numbers above each symbol. STEP 1 STEP 2 STEP 3 STEP 4 Now move the numbersdiagonally downwardsso that they are sitting just below their opposite symbol. You should now have the symbol formula for the compoundiron(III) oxide. Fe O 3 + 2 -

5. WORKING OUT THE FORMULA 2 What is the formula ofaluminium sulfate? Al ( ) SO4 - 3 + 2 STEP 4 STEP 1 STEP 3 STEP 2 Two or more of the following will require brackets in your formula; sulfate ion (SO42-) carbonate ion (CO32-) nitrate ion (NO3-) hydroxide ion (OH-) ammonium ion (NH4+)

6. PRACTISE QUESTION Can you work out the blanks in this table? When you think you’ve worked out the answer click on a question mark check your answer. Acommon ion tablewould be handy!

7. Chemical formula? Number of elements? ATOM KEY hydrogen oxygen HClO3 7 3 H2CO3 HCl3O H3CO2 H3ClO H2CO2 10 3 5 6 carbon Number of atoms? Chemical formula? nitrogen sulfur chlorine

8. EXAM QUESTION 1 Click the answers to see how many marks each response has been awarded by the examiner; 1 mark 1 mark 0 marks The calcium is correct, but the other element is sulfur, not sulfide. 0 marks The ion for sodium is Na+, and oxide is O2-, so the correct formula is Na2O.

9. The six in the picture formula agrees with the six hydrogen atoms in the symbol formula. The one in the picture formula agrees with the one oxygen atom in the symbol formula. The two atoms in the picture formula agrees with the two carbon atoms in the symbol formula.

10. EXAM QUESTION 2 Try to answer these exam questions. Once you’ve had a go, click on the button to see the answer the examiner was looking for; CH4 or H4C

11.  but not  1 6

12. PERIODIC TABLE

13. COMMON ION TABLE