⚛️ Unit C3: Language of Chemistry

Learn symbols, formulae, radicals and how to balance chemical equations

🔤 Symbols & Valencies of Elements

A symbol = short form for an element (1 or 2 letters). First letter is ALWAYS capital.

A valency = combining power of an element (how many bonds it can make).

Element	Symbol	Valency
Hydrogen	H	1
Sodium	Na	1
Potassium	K	1
Chlorine	Cl	1
Silver	Ag	1
Magnesium	Mg	2
Calcium	Ca	2
Oxygen	O	2
Zinc	Zn	2
Aluminium	Al	3
Iron	Fe	2 or 3
Copper	Cu	1 or 2
Lead	Pb	2 or 4

🧠 Diatomic Elements – "Have No Fear Of Ice Cold Beverages"

H₂ – Hydrogen

N₂ – Nitrogen

F₂ – Fluorine

O₂ – Oxygen

I₂ – Iodine

Cl₂ – Chlorine

Br₂ – Bromine

🔢 Working Out Formulae (Swap Valency Method)

Use the "swap valency" method to work out formulae:

Example: Sodium Oxide (Na₂O)

Elements:

Sodium (Na) + Oxygen (O)

Valencies:

Na = 1 O = 2

Swap:

Na gets 2, O gets 1

Formula:

Na₂O → (the "1" subscript is always dropped)

More examples:

Compound	Elements + Valencies	Formula
Calcium chloride	Ca(2) + Cl(1) → swap	CaCl₂
Magnesium oxide	Mg(2) + O(2) → swap → reduce	MgO
Aluminium oxide	Al(3) + O(2) → swap	Al₂O₃
Iron(III) chloride	Fe(3) + Cl(1) → swap	FeCl₃

🔗 Radicals

A radical = a group of atoms combined together, with a formula and a valency.

Radical	Formula	Valency
Hydroxide	OH	1
Ammonium	NH₄	1
Nitrate	NO₃	1
Carbonate	CO₃	2
Sulfate	SO₄	2

Example: Copper(II) Nitrate → Cu(NO₃)₂

Element:

Cu (valency 2)

Radical:

NO₃ (valency 1)

Swap:

Cu gets 1, NO₃ gets 2

Formula:

Cu(NO₃)₂ ← brackets because more than one radical

⚖️ Balancing Chemical Equations

A balanced equation has the same number of atoms of each element on both sides. Atoms are never created or destroyed (Law of Conservation of Mass).

Steps to balance:

Write the word equation
Replace words with symbols/formulae
Count atoms on each side
Add coefficients (numbers in front) to balance — NEVER change the formula
Check your work!

Examples:

H₂ + Cl₂ → 2HCl
2 H on each side ✅ 2 Cl on each side ✅

2H₂ + O₂ → 2H₂O
4 H on each side ✅ 2 O on each side ✅

2Na + 2H₂O → 2NaOH + H₂
Sodium + water → sodium hydroxide + hydrogen

🚫 Important Rule

You can ONLY add coefficients (numbers in front). You must NEVER change the subscripts inside a formula (e.g. you cannot change H₂O to H₃O).

🧠 Quiz Time! Chapter 3

Test what you've learnt! Pick the best answer.