On the basis of the expected charges on the monatomic ions, give the chemical formula of each of the following compounds: (a) magnesium arsenide; (b) indium sulfide; (c) aluminum hydride; (d) hydrogen telluride; (c) bismuth(III) fluoride.

Writing chemical formulas is a fundamental skill in chemistry that allows us to represent compounds clearly and concisely. For example, when writing the formula for magnesium arsenide, we start by understanding that magnesium (Mg) has a +2 charge. Following this, we consider arsenide (As) with a -3 charge. The aim is to combine these ions in a ratio that balances the overall charge of the compound. A simple cross-multiplication method is applied: the charge of magnesium becomes the subscript of arsenide, and vice versa, giving us \( Mg_3As_2 \). The subscript indicates the number of ions needed to balance the charge, ensuring the resulting compound is neutral. This method is universally applicable, whether it's for indium sulfide \( In_2S_3 \), aluminum hydride \( AlH_3 \), or bismuth(III) fluoride \( BiF_3 \). Recognizing the charge of each ion based on its position in the periodic table is key to writing the correct formula.

Monatomic ions are atoms that have lost or gained electrons, which creates a charge. This charge is determined by the atom's group number in the periodic table. For instance, magnesium, which is in group 2, loses two electrons to attain stability, resulting in a +2 charge. Conversely, arsenic, in group 15, gains three electrons, acquiring a -3 charge to achieve a stable electron configuration. When forming compounds, monatomic ions combine in such a way that their total charge is neutralized. This can be determined through the octet rule, where atoms aim to have an outer shell resembling a noble gas, either by shedding electrons to form positive cations or by gaining electrons to form negative anions. Understanding the charges of ions is a crucial step in predicting the ratios in which they combine, which is necessary to write correct chemical formulas.

The periodic table is arranged in columns known as groups that share chemical and physical properties. Elements in the same group typically have similar valence electron configurations, which directly influences their ability to form ions. Group 1 elements lose one electron to form +1 charged ions, while group 16 elements gain two electrons to form -2 charged ions. This predictable behavior facilitates the formation of ionic compounds, such as hydrogen telluride \( H_2Te \), where the group 1 element hydrogen forms a +1 cation and the group 16 element tellurium forms a -2 anion. Group numbers can provide a quick reference for determining the common charges of monatomic ions, though there are exceptions to these patterns. Nevertheless, acknowledging these groups is instrumental in anticipating how different elements will react and in what proportion they will form compounds.