Counting Atoms in Chemical Formulas

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What is a chemical formula?

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A chemical formula is a way of expressing the composition of a substance using symbols for its constituent elements and numerical subscripts to indicate the number of atoms of each element.

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How do you determine the number of atoms in a chemical formula?

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To determine the number of atoms in a chemical formula, identify the elements present and their corresponding subscripts. If an element has no subscript, it is understood to have one atom.

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What does a subscript in a chemical formula indicate?

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A subscript in a chemical formula indicates the number of atoms of the element that precedes it. For example, in H2O, the '2' indicates there are two hydrogen atoms.

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There is 1 carbon atom.

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There is 1 sulfur atom.

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There are 4 atoms total: 2 sodium (Na) and 2 chlorine (Cl) atoms.

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There are 4 carbon atoms.

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There are 4 oxygen atoms.

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There are 3 atoms total: 1 calcium (Ca) and 2 chlorine (Cl) atoms.

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What is the significance of parentheses in chemical formulas?

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Parentheses in chemical formulas indicate that the enclosed group of atoms is a distinct unit. The subscript outside the parentheses applies to all atoms inside.