Chapter 3 of 19

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Tamil Nadu (TNBSE)Class 7 Science★ 6-10 marks in the TN Class 7 Term 1 exam through atoms, elements, compounds and formula questions

Matter Around Us

Samacheer Kalvi (TN State Board) Class 7 Science — Term 1 Chapter 3, Matter Around Us. Atoms, molecules, elements (and the 118 known elements) and compounds, metals and non-metals and their properties, symbols of elements and chemical formulae, with the actual book-back questions, common mistakes and quick revision.

⏱ 15 min readEasy difficulty✓ Free · NCERT-aligned

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Mind Map

The chapter at a glance

Every concept and exam-favourite branch — revisable in 5 minutes.

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Study Guide

Night-before notes

Key points, glossary and the questions most likely to show up.

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By the end of this chapter you'll be able to…

1Define atoms and molecules
2Differentiate elements, compounds and mixtures
3Write symbols of common elements
4Read chemical formulae
5Classify substances

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Why this chapter matters

Atoms, molecules, elements and compounds are the foundation of all chemistry. The element/compound/mixture distinction and chemical formulae are directly tested in the TN Class 7 Term 1 exam.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

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Class 6 — Matter

States of matter.

Matter Around Us — Class 7 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 7 Science, Term 1 — Chapter 3. Atoms, molecules, elements, compounds, metals and non-metals.

1. About this chapter

This chapter covers atoms and molecules, elements and compounds, metals and non-metals, symbols of elements, and chemical formulae.

2. Atoms, molecules, elements and compounds

An atom is the smallest particle of an element; a molecule is the smallest particle of matter that can exist by itself, formed when two or more atoms combine chemically. A molecule of more than three atoms is a polyatomic molecule.
Elements are the simplest pure substances, made of only one kind of atom; there are 118 known elements. A compound forms when atoms of two or more elements combine chemically in a definite proportion (e.g. CO₂ = 1 carbon + 2 oxygen).

3. Metals and non-metals

Metals are lustrous, malleable and ductile and good conductors — e.g. iron, gold, copper. Mercury is a metal that is liquid at room temperature.
Non-metals are usually dull, brittle and poor conductors — e.g. oxygen, hydrogen, sulphur. Graphite is the only non-metal that conducts electricity.
Nitrogen is the most abundant gas in the atmosphere.

4. Symbols and chemical formulae

Each element has a symbol — the first letter is always a capital (and the second, if any, is small). Some symbols come from the Latin or Greek names (Fe for iron, Na for sodium).
A chemical formula is a short, scientific way to represent one molecule of an element or compound (H₂O, CO₂), showing the kinds and numbers of atoms.

5. Worked examples

Example 1. Which non-metal conducts electricity? Graphite.

Example 2. Which metal is liquid at room temperature? Mercury.

Example 3. How many atoms are in CO₂? 3 (1 carbon + 2 oxygen).

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

Which of the following is a metal? — (a) Iron / (b) sulphur. Ans: (a) Iron.
Oxygen, hydrogen and sulphur are examples of — (a) metals / (b) non-metals. Ans: (b) non-metals.
The short, scientific way of representing one molecule is the — (a) symbol / (b) chemical formula. Ans: (b) chemical formula.
The metal that is a liquid at room temperature is — (a) iron / (b) mercury. Ans: (b) mercury.

II. Fill in the blanks 5. The smallest particle of matter that can exist by itself is the molecule. 6. The only non-metal that conducts electricity is graphite. 7. There are 118 known elements. 8. The most abundant gas in the atmosphere is nitrogen. 9. The first letter of an element's symbol is always written in capital.

III. Answer briefly 10. What is a compound? — A pure substance formed when atoms of two or more elements combine chemically in a definite proportion. 11. Name three properties of metals. — Lustrous, malleable and ductile (also good conductors).

7. Common mistakes

Mistake: Saying all non-metals are non-conductors. Fix: Graphite (a non-metal) conducts electricity.
Mistake: Writing an element's symbol starting with a small letter. Fix: The first letter is always capital (Fe, Na, Cl).
Mistake: Confusing a compound with a mixture. Fix: A compound is a chemical combination in a definite proportion.

8. Quick revision

Term 1 · Ch 3 · matter around us.
Molecule = smallest particle that can exist by itself; polyatomic = more than 3 atoms; 118 known elements.
Metals: lustrous, malleable, ductile (mercury liquid); non-metals: oxygen, hydrogen, sulphur (graphite conducts).
Symbols: first letter capital, some from Latin/Greek; chemical formula = short representation of a molecule; nitrogen most abundant gas.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Atom / molecule

atom = smallest particle of an element; molecule = two or more atoms joined

Building blocks.

Element

one kind of atom

H, O, Fe.

Compound vs mixture

chemical (fixed ratio) vs physical (any ratio)

Water vs air.

Chemical formula

kinds and numbers of atoms (H₂O = 2 H + 1 O)

Subscripts count atoms.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Confusing a mixture with a compound

✓ A compound is formed by chemical combination (fixed ratio); a mixture is a physical mix (any ratio).

WATCH OUT

✗ Writing symbols with two capital letters

✓ A two-letter symbol has one capital and one small letter (Na, Cl, Fe).

WATCH OUT

✗ Miscounting atoms in a formula

✓ The subscript gives the number of atoms (H₂O = 2 H + 1 O).

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on metals, non-metals, chemical formula and mercury.

Questions

Fill in the blanks

Molecule, graphite, 118 elements, nitrogen and capital first letter.

Questions

Answer briefly

Compound, properties of metals, symbols.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

Which is a metal: iron or sulphur?

▶ Show solution

Iron.

Q2EASY· MCQ

The metal that is a liquid at room temperature is ____.

▶ Show solution

mercury.

Q3EASY· Fill in the blanks

The only non-metal that conducts electricity is ____.

▶ Show solution

graphite.

Q4EASY· Fill in the blanks

The most abundant gas in the atmosphere is ____.

▶ Show solution

nitrogen.

Q5MEDIUM· Answer briefly

What is a compound?

▶ Show solution

A pure substance formed when atoms of two or more elements combine chemically in a definite proportion (e.g. CO₂).

Q6MEDIUM· Answer briefly

Name three properties of metals.

▶ Show solution

Metals are lustrous, malleable and ductile (and good conductors of heat and electricity).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Term 1 Chapter 3 of Samacheer Kalvi Class 7 Science.
•Matter is made of atoms; a molecule is two or more atoms joined.
•An element has only one kind of atom; a compound is elements combined chemically in a fixed ratio.
•A mixture is a physical mix of substances in any ratio.
•Each element has a symbol (one capital, optional one small letter).
•A chemical formula gives the kinds and numbers of atoms (H₂O = 2 H + 1 O).

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 6-10 marks across matter

Question type	Marks each	Typical count	What it tests
Objective	1	3-4	Definitions, symbols, formulae
Differentiate	2	1	Element vs compound
Classify	2	1	Element/compound/mixture

Prep strategy

Learn the atom/molecule definitions
Use chemical vs physical to classify
Memorise common symbols
Count atoms from subscripts

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Chemistry foundation

Understanding matter underlies all chemical study.

Materials

Knowing elements and compounds helps choose materials.

Everyday substances

Water, salt and air are explained as compounds and mixtures.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Define atom and molecule precisely
Use chemical vs physical to classify
Write symbols with correct capitals
Count atoms using subscripts

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Write the chemical formula and count the atoms in glucose's basic units.
Explain why air is a mixture but carbon dioxide is a compound.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 7 Term 1 ExamHigh

NMMS / Foundation ScienceMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

A compound forms when elements combine chemically in a fixed ratio and gains new properties, while a mixture is just substances physically mixed in any ratio that keep their own properties and can be separated easily.

It shows which elements are present and how many atoms of each are in one molecule — for example, H₂O means each water molecule has two hydrogen atoms and one oxygen atom.

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