Elements

The simplest pure substances

A pure substance can be an element or a compound. Scientists found that the thousands of substances around us are made from a small number of simple substances. These are the elements.

An element is a pure substance that cannot be broken down into simpler substances by any chemical change. It is made of only one kind of atom. We know of more than a hundred elements (118 are named today). About ninety of them are found in nature, and the rest have been made in laboratories.

Examples: hydrogen, oxygen, nitrogen, carbon, iron, copper, gold, sulphur.

Think of the 26 letters of the alphabet. From 26 letters, we make thousands of words. In the same way, from about a hundred elements, nature makes millions of different substances. The elements are the "letters", and the compounds are the "words".

Names and symbols

Each element has a symbol of one or two letters. The first letter is a capital, and the second, if there is one, is a small letter. So $\text{Co}$ is cobalt, but $\text{CO}$ is carbon monoxide, a compound of carbon and oxygen. The capital letters matter.

Most symbols come from the first letters of the English name. A few come from the old Latin names, and these are the ones to learn by heart.

Metals

Most elements are metals. They share these properties:

• They have a shine (lustre) when they are clean.
• They are malleable (they can be beaten into thin sheets) and ductile (they can be drawn into wires).
• They are good conductors of heat and electricity.
• They are sonorous. They make a ringing sound when hit.
• They are usually solid at room temperature. Mercury is a liquid metal.

Examples: gold, silver, copper, iron, aluminium, sodium.

There are exceptions. Sodium and potassium are soft: you can cut them with a knife. Gallium melts in your hand. Most metals are hard and have high melting points, and these are not exceptions but the general rule.

You should find that half a gram of gold can cover a third of a square metre, at less than a tenth of a micrometre thick.

Non-metals

Non-metals have different properties.

• They do not shine, and they are brittle if they are solid.
• They are poor conductors of heat and electricity. (Graphite, a form of carbon, is a conductor, and it is an exception.)
• They are not sonorous.
• They can be solids, liquids or gases. Bromine is a liquid non-metal.

Examples: hydrogen, oxygen, nitrogen, carbon, sulphur, chlorine.

Iodine is a non-metal that does shine a little, as dark crystals. Diamond, a form of carbon, is the hardest natural substance. Nature has many exceptions, and that is why chemists test several properties before they decide.

Metalloids

Some elements have properties between those of metals and non-metals. They are called metalloids. Examples: boron, silicon, germanium and arsenic. Silicon is used to make the chips of computers, because it can conduct a little, in a way that we can control.

Comparing the three

Elements in your life

The air has mainly nitrogen ($78\ \%$) and oxygen ($21\ \%$). Your body is made mainly of oxygen, carbon, hydrogen and nitrogen, with calcium in the bones and iron in the blood. A wire is copper. A coin may be nickel or copper. The lead of a pencil is not lead at all. It is a mixture of graphite (carbon) and clay.

Practise with new numbers

Try it in Python

The program finds which symbols come from Latin names.

Common mistakes

• Writing the symbol with the wrong capital letters. $\text{Co}$ is cobalt, $\text{CO}$ is a compound.
• Thinking that every metal is hard or heavy. Sodium is soft, and lithium is lighter than water.
• Thinking that every non-metal is a gas. Carbon and sulphur are solids, and bromine is a liquid.
• Calling water or salt elements. They are compounds, because they can be broken into simpler substances.

Remember these

• An element has only one kind of atom, and it cannot be broken into simpler substances by a chemical change.
• Elements are metals, non-metals or metalloids.
• Each element has a symbol, such as H, C, O, Na, Fe and Cu. The first letter is a capital, and the second is small.
• Metals shine, are malleable, ductile and sonorous, and conduct heat and electricity. Non-metals mostly do not.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Is common salt an element? Why?

2. Give two properties of metals that you can test with a hammer and a battery.

3. Name a non-metal that conducts electricity, and a metal that is soft enough to cut with a knife.

4. Write the symbols of calcium, chlorine, copper and lead.