Class 9 (Science assignment)

 

Atoms, Elements, and Compounds

Everything around us is made up of tiny particles called atoms. An atom is the smallest unit of matter that retains the properties of an element. Atoms consist of three main particles: protons, neutrons, and electrons. Protons carry a positive charge, electrons carry a negative charge, and neutrons are neutral. The protons and neutrons form the nucleus of the atom, while electrons orbit around it.

An element is a pure substance made entirely of one kind of atom. For example, hydrogen, oxygen, and gold are all elements. Each element has its own chemical properties, which are determined by the number of protons in its atoms, known as the atomic number.

When atoms of different elements combine chemically, they form compounds. A compound is a substance made of two or more elements in a fixed ratio. For example, water (H₂O) is a compound made of hydrogen and oxygen in a 2:1 ratio. Compounds have properties that are different from the elements they are made of.

Understanding atoms, elements, and compounds is fundamental to chemistry because it explains how matter behaves and interacts in the world around us.

Questions:

1. Draw a simple diagram of an atom showing protons, neutrons, and electrons.
2. Explain why elements are considered pure substances.
3. Describe the difference between a mixture and a compound.
4. How can knowing the atomic number help predict the chemical behaviour of an element?
5. Write the chemical formula for a compound formed from two hydrogen atoms and one oxygen atom, and explain the ratio.