Paragraph on “What are chemical elements and compounds?” complete paragraph for Class 9, Class 10, Class 11 and Class 12

What are chemical elements and compounds?

When Water boils into steam or freezes into ice it looks feels very different. However, if steam is cooled down, or ice is heated, they return to liquid water. Both are really just forms of water. Steam is water as a gas and ice is water as a solid. 

If we heat paper instead of water it catches fire and burns into smoke and ash. We cannot get the paper back by cooling because it has really changed. I I we leave an iron nail outside it changes into rust. Again, rust is really different from iron. Both the paper and the iron have joined together with a part of the air (a gas called oxygen) to become new things. On the other hand, if we drop a fizzy indigestion-pill into water, part of it breaks down giving off a gas. This is why it bubbles. Again it has really changed.

Some substances cannot be broken down at all. We call these ‘elements’. The iron that a nail is made of is an example of an element. Elements are pure materials which cannot be split up into anything simpler. The oxygen in the air is also an element. However the rust that we get when iron and oxygen join together cannot be an element, can it ? It is what we call a ‘compound’ — something made by joining elements together. There are less than a hundred natural elements but there are thousands of compounds. As Well as iron and oxygen, some other elements are hydrogen gas, carbon and copper. Examples of compounds are water, salt and polythene.