Chapter 3 · ICSE Class 7 Chemistry (Selina Concise)

Elements, Compounds and Mixtures

Deepen your understanding of elements, compounds, and mixtures, and how to classify substances into each category.

🧪 Chapter 3

Element, compound, and mixture compared using particle diagrams Three circles showing an element with identical atoms, a compound with chemically bonded different atoms, and a mixture with physically combined different substances not bonded together Element Compound Mixture
3.1

Elements and Compounds

Elements contain only one type of atom. Compounds form when elements chemically combine in a fixed ratio, creating a substance with new properties.

1

Is salt (NaCl) an element or compound?

A compound, formed from sodium and chlorine combined chemically

2

Why does a compound have different properties than the elements that form it?

Because chemical bonding rearranges the atoms' electrons, creating an entirely new substance with its own unique properties

3.2

Mixtures

A mixture contains two or more substances physically combined (not chemically bonded), and can be separated by physical methods.

1

Is a mixture of sand and salt easy or hard to separate?

Relatively easy — dissolve in water, filter out the sand, then evaporate the water to recover the salt

2

Why can mixtures be separated by physical methods, but compounds cannot?

Because mixture components aren't chemically bonded, so they retain their individual properties and can be physically separated

Practice

Exercises

1. Is air an element, compound, or mixture?

2. Is water (H₂O) an element, compound, or mixture?

3. Is oxygen gas an element, compound, or mixture?

4. Give one method for separating a mixture.

5. Why can't a compound be separated by simple physical methods?

Next chapter — Atomic Structure ⚛️ →