Elements, Compounds and Mixtures

All materials are made of tiny particles called atoms. Understanding how these atoms are arranged helps us sort substances into elements, compounds, and mixtures.

Elements

• An element contains only one type of atom.
• It cannot be broken down into simpler substances by chemical reactions.
• Examples: oxygen (O), gold (Au), carbon (C), chlorine (Cl).
• Some elements exist as single atoms (He) or as small molecules like O2.

Compounds

• A compound forms when atoms of different elements join by chemical bonds.
• Atoms are combined in a fixed ratio and shown by a chemical formula (for example, H2O, CO2, NaCl).
• A compound has properties different from the elements it is made from (sodium + chlorine → sodium chloride, a safe edible salt).
• Compounds are separated only by chemical reactions (not by simple physical methods).

Mixtures

• A mixture contains two or more substances (elements and/or compounds) not chemically joined.
• The composition can vary; there is no fixed ratio.
• Each substance keeps its own properties.
• Mixtures can be separated by physical methods (filtration, evaporation, distillation, chromatography, magnet).
• Examples: air (gases mixed), seawater (water + salts), brass (copper + zinc), sand and salt.

Particle picture and analogies

Think of letters, words, and trail mix. Letters on their own are like elements. Letters joined in fixed, meaningful words are like compounds. A bowl of different snacks mixed together is like a mixture: you can still pick out each snack.

How to tell which is which

• Element: one type of atom only; symbol like Fe or O2.
• Compound: different atoms bonded in a fixed formula; properties change; needs chemical reaction to split.
• Mixture: substances simply mixed; variable composition; easy physical separation; often shows a range of melting/boiling temperatures.

Common misconceptions: Water is not an element; it is a compound (H2O). Air is not a compound; it is a mixture of gases. A pure-looking clear liquid may still be a mixture if its composition can change.