Loading the formula workspace…
01 / Choose
Your elements
Each tap adds one atom to your formula. The number at the top is the element’s atomic number.
Nonmetal Metal Metalloid
This palette contains the elements used in our practice collection.
02 / Build
Your formula
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An atom-count previewStart with an element above. For water, try two hydrogen atoms and one oxygen atom.
Choose atoms ↑Keep this handy
Formula reference
Open a card for its atom counts and source. Use this reference as often as you like.
Small numbers, useful ideas
How to read a chemical formula
Count each element
In H2O, the little 2 means two hydrogen atoms. Oxygen has no number written after it, so its count is one. One water molecule contains three atoms in total.
In Practice, build the named compound, then check your counts. Hints first show the elements, then their counts. Explore lets you check any combination against this collection.
Molecules and ratios
A molecular formula counts atoms in a molecule. An ionic formula, such as NaCl, describes the simplest ratio of ions in a repeating solid. Sodium chloride has a 1:1 ratio of sodium to chloride ions.
For this activity, enter exactly one displayed formula: H2O for water or NaCl for sodium chloride. A doubled formula will ask you to reduce the counts.
What you’re practicing
The workspace compares atom counts. It does not model bonds, molecular shapes, chemical reactions, or the conditions needed to make a substance. Different substances can share a molecular formula.
Progress saves in this browser when storage is available. You can change the window size without losing your formula. Buttons work with touch, a mouse, Tab, Enter, and Space.
Learn more: ACS: covalent bonding and molecules · ACS: ionic bonding. Individual compound cards link to PubChem.
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