Chemical Formula Week 3 JSS 3 | 9th grade | Basic Science

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Week 3
Subject: Basic Science
Class: JSS 3
Topic: Chemical Formula
Periods: 1st & 2nd
Duration: 40 minutes each

LEARNING OBJECTIVES:

By the end of the lesson, students should be able to:

Compare and contrast the behavior or characteristics of an element in its combined and uncombined states.
Generate the IUPAC names of some chemical formulas.
Determine the valences of radicals.

KEY VOCABULARY WORDS:

Atom – The smallest particle of an element.
Molecule – A Combination of two or more atoms.
Radical – A group of atoms acting as one unit with a charge.
Valence – The combining power of an element or radical.
Formula – Symbolic representation of a compound.

RESOURCES & MATERIALS:

Periodic table of elements
Chart showing radicals and their valences
Whiteboard/Marker
Samples of common compounds (NaCl, H2O, CaCO3)

BUILDING BACKGROUND (Introduction):

Begin by asking students: “What happens when elements like oxygen, hydrogen, or sodium combine with other elements?”
Relate to real-life: cooking salt (NaCl) behaves differently from metallic sodium or chlorine gas.
Explain that chemical formulas help us represent compounds shortly and scientifically.

PERIOD 1

CONTENT DETAILS:

Meaning of Chemical Formula

A chemical formula is a short way of writing the name of a substance using symbols of the elements it contains.
It shows the type and the number of atoms present in a molecule or compound.

Example:

Water = H₂O (2 atoms of hydrogen, 1 atom of oxygen)
Carbon dioxide = CO₂ (1 atom of carbon, 2 atoms of oxygen)

Elements in Combined and Uncombined States

Uncombined state: An element exists alone, e.g., O₂ (oxygen gas), Na (sodium metal).
Combined state: When elements join with others, their properties change, e.g., NaCl (common salt) – safe to eat, while Na and Cl are dangerous alone.

Examples:

Hydrogen (H₂) – explosive gas → Water (H₂O) – safe to drink.
Sodium (Na) – highly reactive metal → Sodium chloride (NaCl) – edible salt.

Valence of Elements and Radicals

Definition: Valence is the number of electrons an atom gains, loses, or shares to form compounds.
Examples of radicals with valences:
- OH⁻ (hydroxide) → 1
- NO₃⁻ (nitrate) → 1
- SO₄²⁻ (sulphate) → 2
- CO₃²⁻ (carbonate) → 2
- PO₄³⁻ (phosphate) → 3

WRAP UP & ASSESSMENT (Period 1):

Ask students: “What is the difference between sodium and table salt?”
Quick exercise: Write the valence of OH⁻, SO₄²⁻, and PO₄³⁻.

PERIOD 2

CONTENT DETAILS:

Writing and Naming Chemical Formula (IUPAC System)

Steps in writing a formula:

Write down the symbols of the elements/radicals.
Write their valences.
Cross-multiply the valences.
Write the formula with correct subscripts.

Examples:

Sodium + Chlorine → Na⁺ (1) and Cl⁻ (1) → NaCl (Sodium chloride).
Calcium + Chlorine → Ca²⁺ (2) and Cl⁻ (1) → CaCl₂ (Calcium chloride).
Aluminium + Sulphate → Al³⁺ (3) and SO₄²⁻ (2) → Al₂(SO₄)₃ (Aluminium sulphate).

Naming Compounds:

First name the metal (positive ion).
Then name the non-metal or radical (negative ion).

Examples:

H₂O → Water
NaOH → Sodium hydroxide
CaCO₃ → Calcium carbonate
KNO₃ → Potassium nitrate

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WRAP UP & ASSESSMENT (Period 2):

The teacher reviews how to write chemical formulas using cross-multiplication.
Classwork: Write formulas for the following and name them:

Potassium + Bromine
Magnesium + Oxygen
Aluminium + Chlorine

ASSIGNMENT:

Write the valences of the following radicals: NO₃⁻, CO₃²⁻, SO₄²⁻, OH⁻, NH₄⁺.
Write the chemical formulas and names of:
- Sodium + Oxygen
- Calcium + Nitrogen
- Potassium + Sulphate

HOD/VP’S COMMENT & ENDORSEMENT:

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