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Ch.3 - Molecules, Compounds & Chemical Equations
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Not the one you use?Change textbook
All textbooksTro 4th EditionCh.3 - Molecules, Compounds & Chemical EquationsProblem 23
Chapter 3, Problem 23

Determine the number of each type of atom in each formula. a. Mg3(PO4)2 b. BaCl2 c. Fe(NO2)2 d. Ca(OH)2

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Identify the subscript numbers in each chemical formula, which indicate the number of atoms of each element present.
For compound a, Mg_3(PO_4)_2: Note that the subscript outside the parentheses multiplies the number of each atom inside the parentheses. Calculate the number of Mg, P, and O atoms.
For compound b, BaCl_2: The subscript directly after Cl indicates the number of Cl atoms. Determine the number of Ba and Cl atoms.
For compound c, Fe(NO_2)_2: The subscript outside the parentheses affects the number of N and O atoms inside. Calculate the number of Fe, N, and O atoms.
For compound d, Ca(OH)_2: The subscript outside the parentheses affects the number of O and H atoms inside. Determine the number of Ca, O, and H 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. Subscripts indicate the number of atoms of each element present in the molecule. For example, in Mg3(PO4)2, the '3' indicates three magnesium atoms, while '(PO4)2' indicates two phosphate groups, each containing one phosphorus and four oxygen atoms.
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Parentheses in Chemical Formulas

Parentheses in chemical formulas are used to group atoms that are part of a polyatomic ion or a molecular unit. The subscript outside the parentheses applies to all atoms within the parentheses. For instance, in Ca(OH)2, the '2' means there are two hydroxide ions (OH) for each calcium atom, resulting in two oxygen and two hydrogen atoms.
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Counting Atoms in Compounds

To determine the total number of each type of atom in a compound, one must carefully account for both the subscripts and any coefficients. This involves multiplying the subscripts by any coefficients and summing the contributions from all parts of the formula. For example, in BaCl2, there is one barium atom and two chlorine atoms, leading to a total count of three atoms.
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Related Practice
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How many atoms are specified by each of these prefixes: mono-, di-, tri-, tetra-, penta-, hexa-?