Chemical Formulas
A formula shows which atoms and how many are in a substance.
About this topic
A chemical formula uses symbols and subscripts to show the types and numbers of atoms in a substance. A molecular formula such as C6H12O6 gives actual atoms in a molecule, an empirical formula such as CH2O gives the simplest ratio, and an ionic formula such as CaCl2 gives the ratio of ions. A structural formula shows how atoms are connected.
The subscript applies to the symbol just before it, and brackets let it apply to a group: in Ca(OH)2 there is one calcium, two oxygens and two hydrogens. A coefficient in front, such as 3H2O, multiplies the whole formula and means three molecules. For ionic compounds, the formula is found by balancing charges: Al3+ and O2- need two aluminium and three oxygen, so Al2O3, using the crisscross method as a shortcut.
Formulas let chemists count atoms, calculate molar masses and write balanced equations. For example, the formula of glucose tells us a single molecule has 24 atoms, 6 carbon, 12 hydrogen and 6 oxygen. Vinegar's acid is CH3COOH, and baking soda is NaHCO3.
Mistakes include changing subscripts to balance equations, which changes the substance, writing lowercase for capital letters (CO versus Co), and forgetting that formulas of ionic compounds are ratios, not molecules.
Key ideas
- Subscripts count atoms
- Parentheses group atoms
- Empirical vs molecular formulas
Quick check
Use cases: where Chemical Formulas helps
- Homework: review the key idea behind Chemical Formulas before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Chemical Formulas without notes.
- Visual learning: play with the interactive lab to see how Chemical Formulas changes when you adjust its inputs.
- Teaching a friend: explain Chemical Formulas in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Chemical Formulas?
A formula shows which atoms and how many are in a substance.
What will I learn in Chemical Formulas?
Subscripts count atoms. Parentheses group atoms. Empirical vs molecular formulas.
Is Chemical Formulas part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Chemical Formulas lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Chemical Formulas?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.