Chemical Reactions and Counting Atoms

Chemical Reactions and Counting Atoms

Chemical Formulas

A chemical formula is a description of the number and kind of atoms found in a single molecule of a substance, using the symbol for each element and a subscript number to state the number of atoms of the element to the left of the subscript

Counting Elements

If asked how many different elements are in a chemical formula, remember that each element symbol starts with a capital letter. But be careful to not count an element twice if repeated in the formula. In HC₂H₃O₂, there areonly three elements, carbon, hydrogen and oxygen, even though there are four capital letters. (The H symbol is repeated twice in the formula.)

Counting Atoms

To count the total number of atoms in a formula, count each symbol without a subscript number as one atom, and then add together all of the subscript numbers. In HC2H3O2, there are 8 atoms: four hydrogen (H), two carbon (C)and two oxygen.

Multiple Choice

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Multiple Choice

How many elements are in C₆H₁₂O₆?

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