Class 8 (Science Assignment)

 

Elements and Compounds

Everything around us is made of matter. Matter is made up of tiny particles called atoms. An element is a pure substance that contains only one type of atom. Elements cannot be broken down into simpler substances by ordinary chemical methods. Examples of elements are oxygen, iron, copper, carbon, and gold.

A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio. The properties of a compound are different from those of the elements that form it. For example, water (H₂O) is a compound made of hydrogen and oxygen. Hydrogen is a highly flammable gas, while oxygen supports burning, but water is a liquid that is used to extinguish fire. Similarly, table salt (NaCl) is a compound formed from sodium and chlorine. Sodium is a highly reactive metal, and chlorine is a poisonous gas, but table salt is safe to eat in small amounts.

Scientists use chemical symbols to represent elements. For example, H stands for hydrogen, O for oxygen, Fe for iron, and Cu for copper. Chemical formulae are used to represent compounds. For example, the formula of water is H₂O, and the formula of carbon dioxide is CO₂.

Understanding elements and compounds helps us explain many natural processes and chemical reactions that occur in our daily lives. It also helps scientists develop new materials, medicines, and technologies.

 

Short Questions

1.     What is an element?

2.     What is a compound?

3.     Write any two examples of elements.

4.     What is the chemical formula of water?

5.     Why are the properties of a compound different from those of its elements?

6.     What do chemical symbols and chemical formulae represent?

7.     Write the chemical symbols of:

o   (a) Iron

o   (b) Copper

o   (c) Oxygen

o   (d) Hydrogen