Question

How many atoms of each kind are represented in the following formulas? For each, name the elements present. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{C}_{3} \mathrm{H}_{7}\), (b) \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (e) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\)

Short answer

Atoms in (a) C:9, H:15; (b) Mg:1, S:1, O:11, H:14; (c) K:1, Al:1, S:2, O:20, H:24; (d) Cu:1, N:2, O:6; (e) C:4, H:10.

Step-by-step solution

Analyze the Compound and Count Atoms for (a)

Break down the compound \(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CO}_{2}\mathrm{C}_{3}\mathrm{H}_{7}\) into its constituent groups: two \(\mathrm{CH}_{3}\) groups, one \(\mathrm{CH}_{2}\) group, a \(\mathrm{CO}_{2}\) group, and a \(\mathrm{C}_{3}\mathrm{H}_{7}\) group. Count the atoms of each element: Carbon atoms = 3 + 2 + 1 + 3 = 9, Hydrogen atoms = 3*2 + 2 + 7 = 15.

Analyze the Compound and Count Atoms for (b)

The compound \(\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}\) is magnesium sulfate heptahydrate. Count the atoms for each element: Magnesium = 1, Sulfur = 1, Oxygen = 4 (from sulfate) + 7*1 (from water) = 11, Hydrogen = 7*2 = 14.

Analyze the Compound and Count Atoms for (c)

For the compound \(\mathrm{KAl}\left(\mathrm{SO}_{4}\right)_{2} \cdot 12 \mathrm{H}_{2}\mathrm{O}\), count the atoms for each element: Potassium = 1, Aluminum = 1, Sulfur = 2*1 = 2, Oxygen = 2*4 (from sulfate) + 12*1 (from water) = 8 + 12 = 20, Hydrogen = 12*2 = 24.

Analyze the Compound and Count Atoms for (d)

Break down the compound \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\): Copper = 1, Nitrogen = 2*1 = 2, Oxygen = 2*3 = 6.

Analyze the Compound and Count Atoms for (e)

Analyze compound \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{COH}\): Carbon atoms = 3 + 1 (from COH) = 4, Hydrogen atoms = 3*3 + 1 = 10.

Key concepts

Atom Counting

Atom counting is a fundamental skill in chemistry that involves determining the number of each type of atom in a chemical formula. It's crucial for understanding the composition of molecules and their reactions. Let's break down the process to make it simple.

Each chemical symbol in a formula represents one atom of that element. If a symbol is followed by a subscript number, that number indicates how many atoms of the element there are. If there's no subscript, it means there is only one atom. When the formula contains parentheses and a subscript outside the parentheses, you multiply the number of each atom inside the parentheses by the subscript.

For example, in the compound \( \text{MgSO}_4 \cdot 7 \text{H}_2 \text{O} \), the subscript 4 after oxygen means there are four oxygen atoms in the sulfate ion, \( \text{SO}_4 \). The \( \text{H}_2 \text{O} \) indicates water molecules, with the coefficient 7 signifying there are seven water molecules, each with two hydrogen and one oxygen atom. In total, we count 11 oxygen atoms (4 from sulfate and 7 from water) and 14 hydrogen atoms (7 times 2 from water).

Learning to count atoms accurately is essential for understanding chemical formulas and preparing for more complex topics in chemistry.

Molecular Composition

Molecular composition refers to the types and quantity of atoms that make up a molecule. This knowledge helps determine the properties of the substance, including its reactivity, polarity, and physical traits such as melting point and solubility.

To understand molecular composition, we start by interpreting the chemical formula, which provides the blueprint of a molecule. The formula presents a molecule's 'recipe', showing which atoms are present and in what ratios. For example, in \( \text{KAl}(\text{SO}_4)_2 \cdot 12 \text{H}_2\text{O} \), the composition includes potassium (K), aluminum (Al), sulfur (S), oxygen (O), and hydrogen (H). Not only do we count individual atoms, but we also note how they are organized into groups, such as sulfate ions \( \text{SO}_4 \) and water molecules \( \text{H}_2\text{O} \).

By understanding the molecular composition, we gain insights into how a molecule behaves both alone and when interacting with other chemicals. This is one of the reasons why knowing how to analyze and interpret chemical formulas is a vital skill in chemistry.

Chemical Nomenclature

Chemical nomenclature is the system of naming chemical substances. It is essential for effective communication within the scientific community and provides a standardized way to reference chemical compounds. There are several rules and conventions for naming compounds, aimed at providing clarity and reducing ambiguity.

For instance, the compound \( \text{MgSO}_4 \cdot 7 \text{H}_2 \text{O} \) is known as magnesium sulfate heptahydrate. 'Magnesium sulfate' tells us about the cation, Mg, and the anion, sulfate (\text{SO}_4). 'Heptahydrate' indicates that there are seven water molecules attached to the compound.

Another example is \( \text{Cu}(\text{NO}_3)_2 \), named copper(II) nitrate. The (II) indicates the oxidation state of the copper ion, which is important for predicting how it will react with other substances. Chemical nomenclature not only conveys what elements are present in a compound but also provides additional information about its structure and properties. It's a language that, once mastered, makes the study of chemistry much more straightforward.