Category Chemical World

SOLIDS, LIQUIDS AND GASES

Chemicals may be solids, liquids or gases. Water is a liquid. When water is cooled to below 0°C it freezes and forms ice, a solid. When it is heated to 100°C it boils and changes to steam, a gas. We say that water can change its ‘state’.

A chemical’s state depends on its temperature. Solids may turn to liquids and gases and then back to solids again, as the temperature rises and falls. We usually see metals and rocks in their solid state. When they’re heated, they become softer. If they’re heated to a high enough temperature, they melt and become liquid.

Ice

Because the molecules in a solid, such as ice, are held firmly together and can only move about a fixed point, they have a definite shape.

Water

As a liquid, water molecules can move around more freely. The ‘shape’ of the water depends on the container.

Water vapour

The molecules in steam can move freely in all directions, spreading further and further apart until they fill their container.

In the Arctic, the temperature is so cold that sea water freezes into huge solid glaciers.

Steam is given off by cooling towers. The water vapour molecules move freely and spread apart.

Picture Credit : Google

Everything that exists — from the Sun in the sky to the centre of the Earth, and from animals to vegetables —is made up of chemicals. Many of these are familiar to us, such as water, salt, sugar, iron and oxygen. Chemicals can be different from each other in many ways. They have different tastes, like sugar and salt, or different appearances, like gold and silver. Chemicals come in many different forms; some are solids, others are liquids or gases.

Our world is composed of thousands of different substances. We call these substances ‘chemicals’. Chemicals make up the air we breathe, the ground we walk on and the food we eat. Even our bodies are a collection of chemicals!

Chemicals are often put into groups. Water, salt, sugar and oxygen are all chemicals. We call them ‘natural’ chemicals. Plastics, detergents and cosmetics are everyday chemicals too. But these do not occur naturally — they are ‘man-made’. Both types of chemicals are useful. Man-made cleaning agents remove dirt from our clothes and natural dyes from plants are used to colour fabrics.

Our food contains many different chemicals such as vitamins, proteins, fats, carbohydrates and sugars. Chemicals give fruit and vegetables their colour.

Water is made of chemicals and without it there would be no life on Earth.

Wool and cotton can be dyed with man-made chemicals or with natural chemicals from plants.

Picture Credit : Google

There are about 100 special chemicals called ‘elements’. There are substances that cannot be broken down into simpler chemicals. The gases oxygen and hydrogen are both elements, so are iron and gold. Every element is made up of tiny particles called ‘atoms’, which are much too small to see, even with a microscope. Oxygen is composed of oxygen atoms; iron is made up of iron atoms.

Atoms can join together to make ‘molecules’. A molecule of an element is formed from only one type of atom. For example, oxygen exists as a molecule of two oxygen atoms joined together.

Combining chemicals

When two different elements combine, they often make a compound which is very different from either of them. The element sodium is a shiny metal. The element chlorine is a green and poisonous gas. Sodium atoms and chlorine atoms can combine to make a very familiar compound — salt! However, we do not make the salt we eat by combining sodium and chlorine. The salt produced from sea water. In cooler countries, salt is mined from underground.

The atoms of one element may join up with the atoms of another element. When this happens, a completely different chemical is formed. For example, when two hydrogen atoms join with an oxygen atom, they make a molecule of water. Chemicals that are made by combining two or more elements are known as ‘compounds’. Water is a compound. Sugar, salt, plastics — in fact, most of the chemicals around us — are compounds. A compound usually has different characteristics to the elements from which it is made.