Nature of Matter: Elements, Compounds, and Mixtures
Class 08 ScienceWhen two or more substances are mixed, where each substance retains its properties, it is called a mixture. The individual substances that make up a mixture are called its components.
The components of a mixture do not react chemically with each other. In some mixtures, the components are easy to see. Such mixtures, where the different components are generally visible with the naked eye or with a magnifying device, are non-uniform in nature.
On the other hand, some mixtures have components that cannot be seen separately even with the help of a microscope. For example, sugar and water particles cannot be seen separately in their mixture. Such types of mixtures, where the components are evenly distributed and cannot be distinguished, are uniform in nature.
Air
Air is a uniform mixture of mainly nitrogen, oxygen, argon, carbon dioxide, and water vapour. Out of these, oxygen is required by most of the living beings to stay alive. It also helps in combustion. Nitrogen, which constitutes about 78% of the air, does not take part in combustion. Air has water vapour in it. When warm air touches a cool surface, the water vapour turns into liquid water, forming tiny droplets.
Lime water turns milky when carbon dioxide reacts with calcium hydroxide to form calcium carbonate (insoluble tiny white particles) and water.
Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
Types of Mixtures
Mixtures could be of several types depending on the physical state of their components.
- Gas and gas: Air
- Gas and liquid: Aerated water (soda water), Oxygen dissolved in water
- Solid and gas: Carbon particles in air
- Liquid and liquid: Acetic acid in water (vinegar), Oil and water
- Solid and liquid: Sand and water, Seawater
- Solid and solid: Baking powder (baking soda and tartaric acid), Alloys
Pure Substances
A pure substance is a kind of matter that cannot be separated into other kinds of matter by any physical process.
Elements
Water is composed of two different constituents - hydrogen and oxygen. Hydrogen and oxygen are pure substances and are termed as elements. Each element is made up of identical particles called atoms.
These particles are different from the particles of any other element. Elements are substances that cannot be further broken down into simpler substances. They are the building blocks of all matter. Some other examples of elements are gold, silver, sulfur, carbon, etc.
Elements can be classified into metals and non-metals. Gold, silver, magnesium, iron, and aluminium are metals, whereas carbon, sulfur, hydrogen, and oxygen are non-metals. Some elements like silicon and boron have intermediate properties between those of metals and non-metals. They are called metalloids.
Compounds
Compounds are formed when different elements combine in fixed ratios to form something entirely new. The properties of compounds are different from those of elements forming that compound. The constituent elements a compound cannot be separated by any physical method.
Molecules of water are made of two different elements: hydrogen and oxygen, combined chemically in a fixed ratio. The ratio of the number of atoms of hydrogen to oxygen in water has been found to be 2:1.
Sodium, a soft metal, and chlorine, a hazardous gas, combine to form sodium chloride, which is made up of particles of sodium and chlorine in a 1:1 ratio.
Minerals
Most rocks are a mixture of minerals, which can be viewed with the eyes, or by using a magnifying glass or a microscope. Some of the minerals are called native minerals, which are pure elements and not compounds. These can be metals, such as gold, silver, copper, etc., or non-metals like sulfur, carbon, etc.
Most of the minerals are compounds made up of more than one element. Some common examples of minerals include quartz, calcite, mica, pyroxene, and olivine.