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Ch.3 - Molecules and Compounds
All textbooksTro 5th EditionCh.3 - Molecules and CompoundsProblem 24a
Chapter 3, Problem 24a

Determine the number of each type of atom in each formula. a. Ca(NO2)2 d. Mg(HCO3)2

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Identify the elements present in the compound: Calcium (Ca), Nitrogen (N), and Oxygen (O).
Recognize that the subscript outside the parentheses applies to all elements inside the parentheses. Here, (NO2)2 means there are 2 NO2 groups.
Calculate the number of Calcium (Ca) atoms: There is no subscript next to Ca, so there is 1 Ca atom.
Calculate the number of Nitrogen (N) atoms: Each NO2 group contains 1 N atom, and there are 2 NO2 groups, so there are 2 N atoms.
Calculate the number of Oxygen (O) atoms: Each NO2 group contains 2 O atoms, and there are 2 NO2 groups, so there are 4 O atoms.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chemical Formula Interpretation

A chemical formula represents the types and numbers of atoms in a compound. In the formula Ca(NO2)2, 'Ca' stands for calcium, while 'NO2' indicates a nitrite group. The subscript '2' outside the parentheses means that there are two nitrite groups in the compound, which affects the total count of nitrogen and oxygen atoms.
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Counting Atoms in Compounds

To determine the number of each type of atom in a compound, one must account for both the elements present and their respective subscripts. For example, in Ca(NO2)2, there is one calcium atom, two nitrogen atoms (from 2 x NO2), and four oxygen atoms (from 2 x 2 in NO2). This systematic counting is essential for understanding the composition of the compound.
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Parentheses in Chemical Formulas

Parentheses in chemical formulas indicate that the enclosed group of atoms is a distinct unit that can be multiplied by a subscript. In Ca(NO2)2, the parentheses around NO2 signify that the entire nitrite group is repeated twice, which is crucial for accurately calculating the total number of each atom in the compound.
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