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What is the difference between elements, compounds and mixtures?

Class 8 ScienceNCERT chapter: Nature of Matter: Elements, Compounds, and Mixturesइसे हिंदी में पढ़ें

Exam-ready answer

An element is a pure substance made of only one kind of atom and cannot be broken into simpler substances by chemical means. A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio by mass. A mixture contains two or more substances mixed physically in any proportion, each keeping its own properties.

Explanation

Elements are the simplest pure substances. Each is made of only one kind of atom, for example iron, copper, oxygen, hydrogen and carbon. An element cannot be broken down into anything simpler by chemical reactions. Elements are broadly grouped as metals, non-metals and metalloids.

A compound forms when elements join chemically in a fixed ratio by mass. Water is a compound of hydrogen and oxygen, always combined in the ratio 1 : 8 by mass. A compound has properties quite different from its elements: hydrogen burns and oxygen supports burning, yet water is used to put out fires. A compound can be broken into its elements only by chemical methods, not by simple physical ones.

A mixture forms when substances are put together without any chemical reaction, in any proportion, like salt in water, air, or sand with iron filings. Each part keeps its own properties and can be separated by physical methods such as filtration, evaporation or using a magnet. Mixing iron filings and sulfur powder gives a mixture; a magnet pulls out the iron. Heating them together forms iron sulfide, a new compound that is not attracted by a magnet.

Points to remember

  1. Element: a pure substance made of only one kind of atom; e.g. iron, oxygen, carbon.
  2. Compound: a pure substance of two or more elements chemically combined in a fixed ratio by mass; e.g. water, carbon dioxide.
  3. Mixture: two or more substances physically mixed in any proportion; e.g. air, salt solution, soil.
  4. A compound's properties differ from its elements; a mixture's components keep their own properties.
  5. Mixtures are separated by physical methods; compounds can be broken into elements only by chemical methods.

Exam tip

Answer in a three-column comparison table with rows for composition, fixed or variable proportion, properties and method of separation. Add one example for each, and quote the iron and sulfur activity to show how a mixture differs from a compound.

Questions students also ask

Is air a mixture or a compound?
Air is a mixture. It contains gases such as nitrogen, oxygen, carbon dioxide and water vapour in proportions that can vary from place to place. Each gas keeps its own properties, and the gases can be separated by physical methods.
What is the difference between homogeneous and heterogeneous mixtures?
In a homogeneous mixture, the components are spread uniformly and cannot be seen separately, like salt dissolved in water. In a heterogeneous mixture, the components are not uniform and can often be seen separately, like sand in water.
Why is water called a compound and not a mixture?
Water is formed when hydrogen and oxygen combine chemically, always in the fixed ratio of 1 : 8 by mass. Its properties are completely different from those of hydrogen and oxygen, and it cannot be separated into them by physical methods.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.