Course 7.2Lesson 3 of 3
A non-metal burns in oxygen to make a non-metal oxide, which is mostly acidic. It dissolves in water to make an acid: carbon dioxide gives carbonic acid, and sulphur dioxide gives sulphurous acid. A few oxides, such as water and carbon monoxide, are neutral. Metal oxides are basic and non-metal oxides are acidic. Non-metals do not give hydrogen with water or dilute acids, because they tend to gain electrons. They combine with hydrogen to make compounds such as HCl and ammonia, and with metals to make ionic compounds.
Try the code and the simulations beside the lesson.
You have studied how metals react with oxygen, water and acids. Now we look at the non-metals. As you will see, most of the rules are the opposite of what we learned about the metals.
A non-metal burns in oxygen and makes a non-metal oxide.
Burning sulphur makes a bright blue flame and a sharp, choking smell. White phosphorus is so eager to burn that it is stored under water. Carbon burns with a red glow.
Most non-metal oxides are acidic. They dissolve in water to make acids, and they turn blue litmus red.
Carbonic acid is the weak acid in a fizzy drink, and it is why rain is slightly acidic. Oxides of sulphur and nitrogen from cars and factories dissolve in rain, and cause acid rain.
A few non-metal oxides are neutral. They do not turn litmus, such as water, , and carbon monoxide, CO.
Remember the rule: metal oxides are basic, non-metal oxides are acidic. A way to remember it: oxides of the metals make bases with water, as in .
You should find that the sulphur dioxide always weighs twice the sulphur, so low-sulphur coal pollutes much less.
Non-metals do not react with water to give hydrogen, and they do not react with dilute acids to give hydrogen. The reason is that these reactions need the element to give electrons to the hydrogen ions, and a non-metal does not give electrons easily. A non-metal tends to gain electrons.
The halogens are special. Chlorine dissolves in water and forms a mixture of two acids, and this is how water is disinfected.
Non-metals combine with hydrogen to make compounds called hydrides.
The second reaction is the base of the fertiliser industry. The ammonia is made on a huge scale and it goes into fertilisers such as urea. Metals do not react with hydrogen in the same way, except a few very reactive ones, such as sodium, which make ionic hydrides.
A non-metal reacts with a metal to make an ionic compound. The metal gives electrons, and the non-metal gains them. We study this in the next course.
When two non-metals react, neither wants to give electrons, and they share them. The product is a covalent compound, such as , or . We study this in the chapter on covalent bonding.
| Metal | Non-metal | |
|---|---|---|
| Oxide | basic | acidic or neutral |
| With dilute acid | gives hydrogen (if reactive) | no reaction |
| With water | gives hydrogen (if very reactive) | no reaction |
| With hydrogen | mostly no reaction | forms hydrides |
| Tends to | lose electrons | gain electrons |
This program finds the masses of oxide when carbon and sulphur burn.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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