Write the name and number of atoms of each element in each of the following compounds: (a) \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) (b) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{Mg}\left(\mathrm{HSO}_{3}\right)_{2}\) (d) \(\mathrm{ZnCl}_{2}\) (e) \(\mathrm{NiCO}_{3}\) (f) \(\mathrm{KMnO}_{4}\) (g) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (h) \(\mathrm{PbCrO}_{4}\)

A chemical formula represents the types and amounts of elements in a compound. It uses element symbols and numerical subscripts. Each symbol stands for an element, while a subscript indicates the number of atoms of that element. For example, in \(\mathrm{H_2O}\), \(\mathrm{H}\) signifies hydrogen, and \(\mathrm{2}\) tells there are two hydrogen atoms; \(\mathrm{O}\) is oxygen, with no subscript implying one oxygen atom. Interpreting chemical formulas helps in understanding the structure and composition of the compound. By knowing this, you can determine how elements combine and interact in chemical reactions.

Atom counting involves determining the number of each type of atom in a chemical formula. This can sometimes be straightforward, as in \(\mathrm{ZnCl_2}\), where there is one zinc (Zn) atom and two chlorine (Cl) atoms. When parentheses are used in chemical formulas, such as \(\mathrm{(NH_4)_3PO_4}\), multiply the subscript outside the parenthesis by the subscripts inside. Here, \(\mathrm{(NH_4)_3}\) signifies 3 ammonium ions—each ion having 4 hydrogen and 1 nitrogen. Therefore, the total count for hydrogen atoms is \(4 \times 3 = 12\). Understanding how to count atoms accurately is crucial for expressing the proper composition of compounds and for balancing chemical reactions.

Element identification is the process of recognizing different types of atoms within a compound. For example, in \(\mathrm{KMnO_4}\), the elements are potassium (K), manganese (Mn), and oxygen (O). Each element is represented by a unique symbol from the periodic table. The ability to identify elements allows us to understand the basic building blocks of matter. For compounds with complex structures, like \(\mathrm{CH_3CH_2CH_2CH_3}\) (butane), recognizing the repeated patterns can simplify how we see the molecule. This foundational knowledge supports the study of how elements and compounds behave in chemical reactions.

Chemical compounds are substances composed of two or more different elements chemically bonded together. They have unique properties that are distinct from the elements they are made of. Examples include water \(\mathrm{H_2O}\) and sodium chloride \(\mathrm{NaCl}\). These compounds can be classified based on the types of bonds holding the elements together: ionic compounds, like \(\mathrm{NaCl}\), consist of ions attracted to each other by electrostatic forces, while covalent compounds, like \(\mathrm{H_2O}\), involve the sharing of electron pairs between atoms. Understanding chemical compounds is essential for studying the interactions and transformations of matter in chemistry.