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ICSE Class 7 Science★ ICSE Class 7 Chemistry · Full Year Coverage · Board: ICSE

Chemistry — Matter, Atomic Structure, Language of Chemistry & Metals

What is EVERYTHING made of? ATOMS. This chapter takes you INSIDE the atom — protons, neutrons, electrons — and teaches you the LANGUAGE chemists use (symbols, formulas, equations). ICSE Class 7 Science.

⏱ 14 min readMedium difficulty✓ Free · NCERT-aligned

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

1Explain the kinetic theory of matter and use it to describe properties of solids, liquids, and gases
2Distinguish physical changes (reversible, no new substance) from chemical changes (new substance formed)
3Distinguish elements, compounds, and mixtures with examples
4State sub-atomic particles: proton (nucleus, +1), neutron (nucleus, 0), electron (orbit, −1)
5Define atomic number (Z = protons) and mass number (A = protons + neutrons); write electronic configurations
6Write chemical formulae using valency cross-multiplication; know key radicals (NH₄⁺, OH⁻, NO₃⁻, SO₄²⁻, CO₃²⁻)
7Compare metals and non-metals under 5 properties (lustre, conduction, malleability, ductility, sonorousness)
8Name 4 methods of corrosion prevention

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Why this chapter matters

This ICSE Class 7 Chemistry chapter introduces atomic structure — the foundation for all subsequent chemistry. The sub-atomic particles table (proton/neutron/electron: location, charge, mass) is tested in every annual exam. Physical vs chemical changes (reversible vs new substance formed) is a standard 3-mark comparison. Writing chemical formulae using cross-multiplication of valencies is a skill tested across Classes 7-10. The metals vs non-metals comparison (malleable, ductile, sonorous, lustrous, conductor) is a reliable table question. Corrosion prevention methods (galvanisation, alloying) are practical chemistry questions.

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Chemistry — Matter, Atomic Structure & The Language of Chemistry

1. Matter and Its Composition

The Kinetic Theory of Matter

All matter is made of TINY PARTICLES (atoms/molecules)
These particles are in CONSTANT MOTION
The particles have SPACES between them

States of Matter (Explained by Kinetic Theory)

State	Particle Arrangement	Motion	Space Between
Solid	Tightly packed, ordered	VIBRATE in place	Very little
Liquid	Loosely packed	SLIDE past each other	Moderate
Gas	Very loose	MOVE FREELY and FAST	Large

2. Physical and Chemical Changes

Physical Change	Chemical Change
NO new substance formed	NEW substance(s) formed
Usually REVERSIBLE	Usually IRREVERSIBLE
Change in state, shape, size	Change in chemical COMPOSITION
Examples: Melting ice, boiling water, tearing paper	Burning paper, rusting iron, cooking food, milk → curd

3. Elements, Compounds and Mixtures

	Element	Compound	Mixture
Composition	ONE kind of atom	TWO OR MORE elements chemically combined in FIXED ratio	Two or more substances physically mixed
Separation	Cannot be broken down	Chemical means ONLY	Physical means
Properties	Own unique properties	DIFFERENT from constituent elements	Each component RETAINS its properties
Example	Iron (Fe), Oxygen (O₂)	Water (H₂O), Salt (NaCl)	Air, soil, salad

4. Atomic Structure

The Sub-Atomic Particles

Particle	Location	Charge	Mass (relative)
Proton	Nucleus	+1	1
Neutron	Nucleus	0 (neutral)	1
Electron	Orbits/shells around nucleus	—1	~0 (negligible)

Key Numbers

Atomic Number (Z) = Number of PROTONS. Defines the ELEMENT.
Mass Number (A) = Number of PROTONS + NEUTRONS.
In a neutral atom: number of electrons = number of protons.

Electronic Configuration

Electrons are arranged in SHELLS around the nucleus.
Rule: 1st shell (K): max 2. 2nd shell (L): max 8. 3rd shell (M): max 8 (for first 20 elements).
Example: Sodium (Z=11): 2, 8, 1.

5. Language of Chemistry

Chemical Symbols

Each ELEMENT has a UNIQUE SYMBOL — one or two letters. First letter CAPITAL. Second letter (if present) SMALL.
Examples: Hydrogen (H). Helium (He). Sodium (Na — from Latin 'Natrium'). Iron (Fe — 'Ferrum').

Radicals (Ions)

Groups of atoms that carry a CHARGE and behave as a SINGLE UNIT.

Radical	Formula	Charge
Ammonium	NH₄	+1
Hydroxide	OH	—1
Nitrate	NO₃	—1
Sulphate	SO₄	—2
Carbonate	CO₃	—2
Phosphate	PO₄	—3

Writing Chemical Formulae

Write the symbols. Write the VALENCIES (combining capacities). CROSS-MULTIPLY (swap the valencies as subscripts). Simplify.

Example: Aluminium (Al³⁺) + Sulphate (SO₄²⁻) → Al₂(SO₄)₃.

Chemical Equations (Word)

A WORD EQUATION describes a reaction:

Zinc + Hydrochloric Acid → Zinc Chloride + Hydrogen
Reactants → Products. 'The arrow means "yields" or "produces."'

6. Metals and Non-Metals

Property	Metals	Non-Metals
Appearance	Shiny (lustrous)	Dull
Conduction	Good conductors of heat & electricity	Poor conductors (insulators)
Malleability	Malleable (can be beaten into sheets)	BRITTLE
Ductility	Ductile (can be drawn into wires)	Not ductile
Sonorous	Produce SOUND when struck (ringing)	Not sonorous

Uses of Common Metals

Iron: Construction, bridges, tools, vehicles
Copper: Electrical wiring, plumbing. Excellent conductor.
Aluminium: Aircraft (lightweight), foil, cans. Does NOT rust (forms protective oxide layer).
Gold/Silver: Jewellery. Unreactive (don't tarnish easily).

Corrosion

Metals react with air and water → RUST or TARNISH. Prevention: painting, oiling, galvanisation (coating with zinc), alloying (stainless steel = iron + chromium + nickel).

Key formulas & results

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

Atomic Structure, Chemical Language, and Metals

KINETIC THEORY: All matter = tiny particles (atoms/molecules). In CONSTANT MOTION. SPACES between particles. MORE HEAT = faster motion. STATES: Solid (tightly packed, vibrate in place, very little space). Liquid (loosely packed, slide past each other, moderate space). Gas (very loose, move freely and fast, large space). PHYSICAL CHANGE: NO new substance. Usually REVERSIBLE. Change in state/shape/size. Examples: melting ice, boiling water, tearing paper. CHEMICAL CHANGE: NEW substance(s) formed. Usually IRREVERSIBLE. Change in chemical composition. Examples: burning paper, rusting iron, cooking food, milk→curd. ELEMENT vs COMPOUND vs MIXTURE: Element = ONE kind of atom (Fe, O₂). Compound = 2+ elements chemically combined in FIXED ratio, cannot be separated physically (H₂O, NaCl). Mixture = substances physically mixed, each retains its properties, separated physically (air, soil, salad). ATOMIC STRUCTURE: PROTON: in nucleus, charge +1, mass 1. NEUTRON: in nucleus, charge 0 (neutral), mass 1. ELECTRON: orbits around nucleus, charge −1, mass ~0 (negligible). NEUTRAL ATOM: protons = electrons. ATOMIC NUMBER (Z) = number of protons. MASS NUMBER (A) = protons + neutrons. Neutrons = A − Z. ELECTRONIC CONFIGURATION: Shell capacities — K (1st): max 2. L (2nd): max 8. M (3rd): max 8 (first 20 elements). Example: Sodium Z=11: 2,8,1. CHEMICAL SYMBOLS: One capital + optional small letter. H, He, Na (Natrium), Fe (Ferrum), Au (Aurum), Ag (Argentum). KEY RADICALS: Ammonium (NH₄⁺). Hydroxide (OH⁻). Nitrate (NO₃⁻). Sulphate (SO₄²⁻). Carbonate (CO₃²⁻). Phosphate (PO₄³⁻). FORMULA WRITING (cross-multiply): Al³⁺ + SO₄²⁻ → Al₂(SO₄)₃ (swap valencies as subscripts, simplify). METALS vs NON-METALS: Metals: LUSTROUS (shiny), good CONDUCTORS, MALLEABLE (beaten into sheets), DUCTILE (drawn into wire), SONOROUS (ring when struck). Non-metals: DULL, poor conductors (insulators), BRITTLE, not ductile, not sonorous. EXCEPTION: Graphite (carbon) is a non-metal but conducts electricity. USES: Iron (construction), Copper (electrical wiring), Aluminium (aircraft — lightweight, forms protective oxide). CORROSION PREVENTION: Painting/oiling (barrier). Galvanisation (zinc coating). Alloying (stainless steel = iron + chromium + nickel). Electroplating.

ICSE CLASS 7 CHEMISTRY KEY TRAPS: (1) ATOMIC NUMBER Z = PROTONS (not mass number). The atomic number uniquely defines the element. (2) NEUTRAL ATOM: electrons = protons. CATION (positive ion): electrons < protons (lost electrons). ANION (negative ion): electrons > protons (gained electrons). (3) PHYSICAL vs CHEMICAL CHANGE: Burning is CHEMICAL (new substance: ash, CO₂, H₂O). Melting is PHYSICAL (same substance: ice→water). Rusting = CHEMICAL (Fe₂O₃ formed, DIFFERENT from iron). (4) CROSS-MULTIPLY FOR FORMULAE: Write metal first. Write its valency above. Write non-metal. Write its valency above. SWAP the valencies as subscripts. Simplify (divide by common factor). (5) EXCEPTION: HYDROGEN is a non-metal but it is placed in Group 1 of the periodic table (because it has 1 valence electron).

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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

✗ Writing incorrect chemical formulas by adding valencies instead of cross-multiplying

✓ The CROSS-MULTIPLY rule for writing formulas: (1) Write the symbols with their valencies: Al³⁺ and Cl⁻ (valencies 3 and 1). (2) SWAP the valencies as SUBSCRIPTS: Al gets subscript 1 (from Cl's valency), Cl gets subscript 3 (from Al's valency). (3) Result: Al₁Cl₃ = AlCl₃. Another example: Mg²⁺ and O²⁻: swap → Mg₂O₂ → SIMPLIFY by dividing by 2 → MgO. RADICALS: For Al₂(SO₄)₃ — Al is +3, SO₄ is −2. Cross: Al gets subscript 2, SO₄ gets subscript 3 → Al₂(SO₄)₃. Always put brackets around multi-atom radicals before adding subscript.

Practice problems

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

Q1MEDIUM· atomic-structure-formula-writing

An element has atomic number 17 and mass number 35. (a) Name the element. (b) State the number of protons, neutrons, and electrons. (c) Write its electronic configuration. (d) Write the formula for its compound with sodium.

▶ Show solution

(a) ELEMENT: Atomic number 17 = CHLORINE (Cl). (b) PARTICLES: Protons = 17 (always equals atomic number). Electrons = 17 (same as protons in neutral atom). Neutrons = Mass number − Atomic number = 35 − 17 = 18 neutrons. (c) ELECTRONIC CONFIGURATION: Shell K (max 2): 2. Shell L (max 8): 8. Shell M: 17 − 2 − 8 = 7 electrons. Configuration: 2, 8, 7. (d) FORMULA WITH SODIUM: Sodium (Na) has valency +1. Chlorine (Cl) has valency −1. Cross-multiply: Na gets subscript 1 (from Cl's 1), Cl gets subscript 1 (from Na's 1). Formula = NaCl (sodium chloride — common salt). VERIFICATION: +1 from Na + (−1) from Cl = 0 (neutral compound) ✓.

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