On a clean polished surface, lead is as shiny as cooking foil. On roofs, the lead loses its shine as the surface reacts with air and moisture. We can use careful weighing to find the masses of lead and oxygen that combine together.
The masses of lead are the same here. The masses of oxygen are in the ratio of 0.8:1.6 or 1:2.
The two elements oxygen and nitrogen also combine to give more than one oxide.
… ratio
95FIGURE 3:Lead
loses its shine.
By dividing all the oxygen values by the smallest one (57) we get the following ratio of oxygen combined with the same amount of nitrogen, 1:2:3:4
What would the ratio be for 285 g oxygen with the same mass of nitrogen?
What is the simplest ratio of the elements in glucose C6H12O6?
If you heat lead oxides, they turn into different oxides. How could you tell that this has happened?
When you heat magnesium in air, it burns to leave a white ash. The reaction is violent, so we use small samples such as 0.6 mg magnesium. How would you expect the mass to change and how precise should the mass readings be?
Scientists need to exchange their results to check if they are right. This is why they must use the same units. On one space flight, things went wrong because the two construction teams building the
spacecraft had used different units. Mass of Mass of oxygen (g) nitrogen (g) 57 100 114 100 171 100 228 100
Mass of Mass of Colour of oxygen (g) lead (g) oxide
1.6 10 Brown
For each of the following statements write T if the statement is true or F if it is false.
a Mixtures and compounds are the same.
b It is easy to separate mixtures.
c Most of the elements in the Periodic Table are metals.
d One state of matter is called a solid.
Copy the sentences a–d into your exercise book. Use the following words to help you answer the questions. The words can be used once, more than once, or not at all.
conduct insulator mercury non-metals
sodium symbols
a All metals can ______ electricity.
b There is a liquid metal called ______.
c Chemical ______ are a useful shorthand for the elements.
d Most elements are either metals or ______.
Copy the columns below into your exercise book. Draw straight lines to join the word with the correct description.
Word Description
a compound chemical shorthand
b element two or more elements not combined
c symbol simple material
d mixture two or more elements that are combined
Copy the columns below into your exercise book. Choose the correct symbol or formula to match one of the names from this list.
diamond nitrogen oxygen water
Symbol or formula Name
a O2 a b C b c H2O c d N2 d
Practice questions
96Copy the table below into your exercise book. Identify the type of element by placing a tick in the correct column.
Name Metal Metalloid Non-metal
a silicon
b carbon
c oxygen
d iron
Copy the columns below into your exercise book. Match the mixtures with the method of separation by drawing a straight line between them. Each method may be used only once.
Mixture Separation method chosen
a iron and gold stir with water, one dissolves
b sulphur and iron cannot be separated, it is a compound
c carbon and salt dissolve one in acid
d zinc sulphide magnet
What are the simplest numerical ratios of elements in each of the following compounds?
a Pb3O4 b C12H22O11
c P4O10 d H2O2
a Use the following experimental data to deduce the ratio of sulphur to the other
element in the compounds.
Mass of element (g) Mass of sulphur (g)
i 50 15.6
ii 50 23.4
b If compound (i) contains two sulphur atoms for each one of the other element,
how many sulphur atoms are there in compound (ii)?
Copper oxide (CuO) reacts with hydrogen when heated to leave a brown solid and a colourless liquid.
a Identify the products.
b Write a symbol equation for the reaction.
c When the still hot product is exposed to air, it turns black.
Suggest a reason why.
Topic Summary
✩I know how many elements there are. Page 80
✩I know that atoms can join up. Page 80
✩I can describe the differences between solids, liquids and gases. Page 85
✩I know that the Periodic Table displays the elements. Page 85
✩I know that we use special symbols for the elements. Page 85
✩I know the difference between atoms and molecules. Page 80
✩I know some examples of common chemical symbols. Page 82
✩I know some differences between metals and non-metals. Page 84
✩I can correctly use the words brittle, malleable and ductile. Page 84
✩I know that the Periodic Table shows patterns of elements. Page 85
✩I know how compounds and mixtures are different. Page 91
✩I can recognise some chemical symbols. Page 93
✩I know some examples of molecules. Page 80
✩I can identify elements as metals or non-metals. Page 84
✩I can use the Periodic Table to classify elements. Page 85
✩I can distinguish between compounds and mixtures by their properties. Page 90
✩I can write chemical symbols from names. Page 92
✩I can count the atoms in the formula of a molecule. Page 80
✩I know the characteristic properties of metals and non-metals. Page 84
✩I know the symbols of many common elements. Page 85
✩I know that there is a gradation in properties in the Periodic Table. Page 85
✩I know in what ways the properties of mixtures differ from those of compounds. Page 91
✩I can understand how to use word equations. Page 93
✩I can convert word equations into symbol equations. Page 93
✩I can calculate and explain mass changes in reactions. Page 95
✩I can predict whether the mass will increase or decrease in a particular
chemical reaction. Page 95
1 Which is simpler, an element or a compound?
2 What do we call the shorthand for
elements?
3 What does it mean if something is
brittle?
4 Which is more brittle, plasticine or glass?
5 What sorts of materials are displayed in
the Periodic Table?
6 What are the two major categories of
elements?
7 Which is easier to separate, a
compound or a mixture?
8 What are the three states of matter?
9 What is the smallest possible number
of atoms in one molecule?
10 How would you write a sulphur
molecule containing eight atoms?
11 How many compounds are there in
salty water?
12 How many different elements are there
in glucose, C6H12O6?
True or False?
If a statement is false then rewrite it so it is correct.
1 There are three states of matter. 2 Metals such as gold and copper are
elements.
3 The building blocks of elements are
molecules.
4 Malleable means bending without
breaking.
5 Ductile materials are good for wires. 6 You can separate a mixture of iron and
nickel using a magnet.
7 Bromine and mercury are both liquid
elements.
8 Most elements are non-metals. 9 Elements always combine in fixed
proportions by mass.
10 Water is an element.
11 Chemical symbols only use capital
letters.
12 The symbol Au means the element gold.
Literacy Activity
Write a paragraph as if you were a water molecule evaporating from the sea, falling as snow and ending up in a glacier.
ICT Activity
Choose 15 elements from the Periodic Table. Type a table giving their names and symbols and whether they are metals or non-metals.
Topic Quiz
100