The metals and non-metals

Two groups of elements Look again at the Periodic Table on page 31. The zig-zag line separates the elements into two groups: metals and non-metals. The non-metals lie to the right of the line, except for hydrogen. As you can see, there are many more metals than non-metals. In fact over 80% of the known elements are metals.

What is the difference between them? The metals and non-metals have very different general properties. Look at this table: The properties in the last two rows above are called chemical properties, since they are about chemical change. The others are physical properties. You will find out more about many of those properties later. Exceptions to those properties The properties above are general properties of metals and non-metals. But there are exceptions. For example: not all metals are hard solids. You can cut sodium and potassiuml with a knife, and mercury is a liquid at room temperature. hydrogen is a non-metal, but forms positive ions (H1) like metals do.l carbon is a non-metal, but one form of it (graphite) is a goodl conductor; another form (diamond) is very hard, with a very high melting point. General properties of metals General properties of non-metals do not conduct electricity or heatl good conductors of electricity and heat l high melting and boiling points – which meansl they are solid at room temperature lower melting and boiling points – many are gasesl at room temperature solid non-metals break up easily – they are brittlel hard, strong, do not shatter if you hammer them l can be hammered into different shapes (they are malleable)l and drawn out to make wires (they are ductile) solid non-metals are not malleable or ductile – they are brittlel look dull, in the solid statel look shiny when they are polished l solid non-metals break up when you strike theml make a ringing noise when struck – they are sonorous l solid non-metals have low densityl have high density – they feel ‘heavy’ l form positive ions when they react.l For example sodium forms sodium ions (Na1). You will learn about ions in Chapter 4. often form negative ions when they react.l For example oxygen forms oxide ions (O22). react with oxygen to form oxides that are bases.l (In other words, the oxides can neutralise acids.) react with oxygen to form oxides that are acidic.l (Their aqueous solutions will turn litmus red.)

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Carbon dioxide The gas carbon dioxide (CO2) occurs naturally in air. It is also a product in these three reactions: 1 The combustion of carbon compounds in plenty of air. For example, when natural gas (methane) burns in plenty of air, the reaction is: CH4 (g) 1 2O2 (g) CO2 (g) 1 2H2O (l) 2 The reaction between glucose and oxygen, in your body cells: C6H12O6 (aq) 1 6O2 (g) 6CO2 (g) 1 6H2O (l) This is called respiration. You breathe out the carbon dioxide. 3 The reaction between dilute acids and carbonates. For example between hydrochloric acid and marble chips (calcium carbonate): CaCO3 (s) 1 2HCl (aq) CaCl2 (aq) 1 CO2 (g) 1 H2O (l) Properties of carbon dioxide 1 It is a colourless gas, with no smell. 2 It is much heavier than air. 3 Things will not burn in it. We say it does not support combustion. 4 It is slightly soluble in water, forming carbonic acid, H2CO3. Carbon monoxide Carbon monoxide (CO) forms when carbon compounds burn in too little oxygen. For example, when methane burns in insufficient oxygen: 2CH4 (g) 1 3O2 (g) 2CO (g) 1 4H2O (l) It is a deadly poisonous gas. It binds to the haemoglobin in red blood cells, and prevents it from carrying oxygen around the body. So victims die from oxygen starvation. Carbon monoxide has no smell, which makes it hard to detect. So it is important to have gas heaters and boilers checked regularly, to make sure the air supply is not blocked by soot. Carbonates Carbonates are compounds that contain the carbonate ion, CO3 22. One example is calcium carbonate, CaCO3, which occurs naturally as limestone, chalk and marble. These are the main properties of carbonates: 1 They are insoluble in water – except for sodium, potassium, and ammonium carbonates, which are soluble. 2 They react with acids to form a salt, water, and carbon dioxide. 3 Most of them break down on heating, to an oxide and carbon dioxide: CaCO3 (s) CaO (s) 1 CO2 (g) calcium carbonate calcium oxide carbon dioxide (limestone) (lime) But sodium and potassium carbonates do not break down, since the compounds of these reactive metals are more stable.

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Carbon dioxide and methane are greenhouse gases Carbon dioxide and methane are both greenhouse gases. That means they absorb heat in the atmosphere, and prevent it from escaping into space. This is how greenhouse gases work: atmosphere atmosphere Sun Earth 1 The sun sends out energy as light and UV rays. 2 These warm the Earth, which reflects some of the energy away again, as heat. 3 Some of this heat escapes from the atmosphere. 4 But some is absorbed by greenhouse gases in the atmosphere. So the air, and Earth, are warmed. There are several greenhouse gases. Carbon dioxide and methane are the two main ones we add to the atmosphere, through human activity. There is much more carbon dioxide than methane in the atmosphere. But the levels of both are rising: The level of carbon dioxide is rising because we burn more fossil fuell each year. The carbon dioxide from this goes into the atmosphere. It cannot escape into space, and the ocean can dissolve only some of it. The level of methane is rising because there is an increase in animall farming, and rice farming, around the world – and more and more landfill sites. We need greenhouse gases. Without them, we would freeze to death at night, when the sun was not shining. But many scientists think the level of greenhouse gases is now so high that it is causing global warming. Global warming Measurements show that average temperatures around the world are rising. We call this global warming. Why is it happening? Some scientists say it is a natural change, like similar changes in the past. However, a panel of scientists from around the world examined all the data, and concluded that greenhouse gases are almost certainly the main cause. They picked out carbon dioxide as the main culprit. The rise in average temperatures over time appears to match the rise in carbon dioxide levels over time. Compare the two graphs on the right. Carbon dioxide and global mean temperatures Concentration of CO2 in the atmosphere/ parts per million 380 340 300 14.6 14.2 13.8 13.4 1940 1960 1980 2000 Year 1880 1900 1920 Estimated global mean temperature/ °C Two methane manufacturers.p Some non-metal s and their compound s 238 Greenhouse gases, and global warming Climate change Air temperature affects rainfall, and cloud cover, and wind patterns. So as average temperatures rise, climates around the world change too. Scientists try to predict what will happen, using computer models. They cannot make really good predictions yet, because they do not fully understand the links between weather, and clouds, and the ocean. But they do predict that: some places with quite a lot of rain will become very dry, and otherl places will get much wetter. melting land-ice in the Arctic and Antarctica will cause sea levels tol rise, so low-lying countries will be at risk of flooding. storms, floods, and wildfires will be more frequent and severe.l species that cannot adapt to the changing climate will die out.l more drought is likely, which will led to famine – so more people willl become refugees. Most experts agree that climate change is already underway.

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