Paragraph on “What is an Atom?” complete paragraph for Class 9, Class 10, Class 11 and Class 12

What is an Atom?

Suppose we were to take a piece of an element, say iron, and keep dividing it up into smaller and smaller pieces. The smallest bit of iron we could have would he an ‘atom’. Each element has its own atoms. All iron atoms are alike. All oxygen atoms are alike. But iron atoms are different from oxygen atoms.

Look at the diagram of an oxygen atom. In the middle is what we call the ‘nucleus’. Around the nucleus are several tiny particles which circle around it very, very fast. These are called ‘electrons’. Oxygen atoms always have eight electrons, like the one shown. The atoms of other elements also have a nucleus and electrons but each element has a different number of electrons in its atoms. Hydrogen atoms are very simple and have only one electron. Iron atoms have 26 electrons.

Water is a compound of hydrogen and oxygen. You can make water by burning hydrogen gas in air. The smallest possible bit of a compound is called a ‘molecule’. A glass of water contains millions and millions of i molecules. The molecules in steam and in ice are just the same — still water molecules. The only difference is that in steam the molecules are a long way apart while in ice they are packed close together.

Each water molecule is made up of one oxygen atom joined with two hydrogen atoms. As the diagram shows, the three atoms share some of their electrons. The oxygen atom in the middle had eight electrons to begin with and the hydrogen atoms had one each. The new water molecule has ten altogether. The fact that some electrons are shared is what holds the molecules together.