Define the molecular formula of a compound as the number and type of different atoms in one molecule

What is a Molecular Formula?

A molecular formula tells you the exact number and type of atoms in one molecule of a compound. Think of it like a recipe that lists every ingredient and how many of each you need to bake a single cake. ⚗️

For example:

• Water – \$H_2O\$: 2 hydrogen atoms + 1 oxygen atom.
• Carbon dioxide – \$CO_2\$: 1 carbon atom + 2 oxygen atoms.
• Glucose – \$C6H{12}O_6\$: 6 carbon, 12 hydrogen, 6 oxygen.

Reading a Formula – The Lego Analogy

Imagine each element is a different Lego brick colour. The symbol (e.g., H, C, O) is the brick type, and the subscript number tells you how many bricks of that colour you need. If no number is written, it means you need just one brick. 🧩

Empirical vs. Molecular Formula

Empirical formula gives the simplest whole‑number ratio of atoms. Molecular formula gives the actual count in one molecule.

Example: For glucose, the empirical formula is \$CH2O\$ (the simplest ratio), but the molecular formula is \$C6H{12}O6\$ (the real count).

Common Compounds – Quick Reference

Exam Tips 📚

• Always write the formula in the correct order: C (carbon) first, then H (hydrogen), followed by other elements alphabetically.
• If a subscript is missing, remember it means 1.
• When converting between mass and moles, use the molar mass derived from the molecular formula.
• Check the question for any given mass or volume – you may need to find the number of molecules or moles.
• Practice writing formulas from names and vice versa; this builds confidence for the exam.