Question

For each of the following pairs of elements, state whether the binary compound they form is likely to be ionic or covalent. Write the empirical formula and name of the compound: (a) I and Cl, (b) \(\mathrm{Mg}\) and \(\mathrm{F}\).

Short answer

(a) ICl, iodine monochloride - covalent; (b) MgF2, magnesium fluoride - ionic.

Step-by-step solution

Determine Bond Type for I and Cl

To determine if the bond between iodine (I) and chlorine (Cl) is ionic or covalent, we look at their positions on the periodic table. Both iodine and chlorine are nonmetals, which typically form covalent bonds. Thus, the compound is covalent.

Empirical Formula and Name for Iodine and Chlorine

Since the bond is covalent, we consider the tendency to form a molecule with one atom of each element. The empirical formula is \( \text{ICl} \). The name of the compound is iodine monochloride.

Determine Bond Type for Mg and F

Magnesium (Mg) is a metal, and fluorine (F) is a nonmetal. Typically, metal and nonmetal combinations form ionic compounds due to the transfer of electrons from metal to nonmetal. Therefore, the compound is ionic.

Empirical Formula and Name for Magnesium and Fluorine

Because the bond is ionic, we consider the charges: magnesium forms \( \text{Mg}^{2+} \) ions and fluorine forms \( \text{F}^- \) ions. To balance the charges, one Mg needs two F atoms. Thus, the empirical formula is \( \text{MgF}_2 \). The name of the compound is magnesium fluoride.

Key concepts

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, creating ions. This typically occurs between metals and nonmetals. Metals tend to lose electrons to become positively charged cations, while nonmetals gain those electrons to become negatively charged anions.
This exchange of electrons results in a strong attraction between the positively and negatively charged ions, forming an ionic bond.
Ionic compounds generally have high melting and boiling points because of these strong attractions. For instance, in the formation of magnesium fluoride, an electron from magnesium is transferred to fluorine. Magnesium becomes a cation (\(\text{Mg}^{2+}\)), and fluorine becomes an anion (\(\text{F}^{-}\)). Together, they form the compound \(\text{MgF}_2\), which is stable and neutral in charge.

Covalent Bonds

Covalent bonds are formed when two atoms share electrons in order to achieve a full valence shell and attain stability. Unlike ionic bonds, covalent bonds usually occur between nonmetal atoms.
During covalent bond formation, atoms share specific pairs of electrons, effectively holding them together. For example, a covalent compound like iodine monochloride (\(\text{ICl}\)) forms when iodine and chlorine, both nonmetals, share one pair of electrons.
Covalent bonds can be single, double, or triple, depending on the number of shared electrons. This sharing leads to the formation of molecules with specific shapes and angles, contributing to the diverse physical properties of covalent compounds. Some common properties include lower melting and boiling points compared to ionic compounds, and they do not conduct electricity in the solid state.

Empirical Formulas

Empirical formulas represent the simplest whole-number ratio of atoms in a compound. They are not always the same as the molecular formula, which shows the exact number of atoms in a molecule.
An empirical formula provides a basic understanding of the proportion of each element in a compound. For instance, \(\text{MgF}_2\) is the empirical formula for magnesium fluoride, showing a 1:2 ratio of magnesium to fluorine.
In covalent compounds like iodine monochloride, their empirical formula is often the same as their molecular formula because covalent compounds often involve simple ratios. Understanding these formulas helps in predicting how elements combine and what kinds of compounds they form, based on their ratios.

Naming Compounds

Naming chemical compounds is essential for clear communication in chemistry. Two major systems exist: for ionic compounds and covalent compounds.
For ionic compounds, names are straightforward. The metal (cation) is named first, followed by the nonmetal (anion) with an "ide" ending. For example, \(\text{MgF}_2\) is named magnesium fluoride. The name indicates the presence of a magnesium ion and fluoride ions in the compound.
Covalent compounds use a different system involving prefixes to indicate the number of each type of atom present. Common prefixes include mono-, di-, and tri-. In \(\text{ICl}\), the name is iodine monochloride, where "mono-" signifies one chlorine atom bonded with iodine. Naming rules provide consistency and understanding when discussing and researching chemical compounds.