Question

Classify each of the following as ionic or covalent, and name each: a. \(\mathrm{Li}_{2} \mathrm{O}\) b. \(\mathrm{Cr}\left(\mathrm{NO}_{3}\right)_{2}\) c. \(\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}\)

Short answer

a. Ionic, Lithium Oxideb. Ionic, Chromium(II) Nitratec. Ionic, Magnesium Bicarbonate

Step-by-step solution

Determine Ionic or Covalent - \( \mathrm{Li}_2 \mathrm{O} \)

Identify the types of elements in the compound. \( \mathrm{Li} \) is a metal and \( \mathrm{O} \) is a non-metal. Compounds formed between metals and non-metals are typically ionic.

Name the Compound - \( \mathrm{Li}_2 \mathrm{O} \)

The name of an ionic compound is derived from the names of the cation and anion. \( \mathrm{Li}_2 \mathrm{O} \) is named Lithium Oxide.

Determine Ionic or Covalent - \( \mathrm{Cr} \left( \mathrm{NO}_3 \right)_2 \)

Identify the types of elements in the compound. \( \mathrm{Cr} \) is a metal and \( \mathrm{NO}_3 \) is a polyatomic ion, generally consisting of non-metals. Compounds formed between metals and a group of non-metals (polyatomic ions) are typically ionic.

Name the Compound - \( \mathrm{Cr} \left( \mathrm{NO}_3 \right)_2 \)

The name of an ionic compound containing a transition metal is derived from the cation, its oxidation state, and the anion. \( \mathrm{Cr} \) has a +2 oxidation state and \( \mathrm{NO}_3 \) is Nitrate. The name is Chromium(II) Nitrate.

Determine Ionic or Covalent - \( \mathrm{Mg} \left( \mathrm{HCO}_3 \right)_2 \)

Identify the types of elements in the compound. \( \mathrm{Mg} \) is a metal and \( \mathrm{HCO}_3 \) is a polyatomic ion. Compounds formed between metals and a group of non-metals (polyatomic ions) are typically ionic.

Name the Compound - \( \mathrm{Mg} \left( \mathrm{HCO}_3 \right)_2 \)

The name of an ionic compound is derived from the names of the cation and anion. \( \mathrm{Mg} \left( \mathrm{HCO}_3 \right)_2 \) is named Magnesium Bicarbonate.

Key concepts

Types of Chemical Bonds

Chemical bonds hold atoms together in a compound. There are two main types: ionic and covalent bonds.
Ionic bonds form between metals and non-metals. Metals, like Lithium (Li) or Magnesium (Mg), lose electrons and become positively charged ions. Non-metals, like Oxygen (O) or polyatomic ions (e.g., Nitrate ions \((\text{NO}_3^-)\)), gain those electrons and become negatively charged. The attraction between these oppositely charged ions forms the ionic bond.
Covalent bonds form when two non-metals share electrons. This bond mainly exists within molecules like oxygen gas \((\text{O}_2)\) or water \((\text{H}_2\text{O})\). Understanding the type of elements involved helps predict the type of bond. For instance, considering the exercise, since \(\text{Li}_2\text{O}\) consists of Lithium (metal) and Oxygen (non-metal), it forms an ionic bond.

Naming Ionic Compounds

Naming ionic compounds follows specific rules based on the components involved. The name generally derives from the metal (cation) and the non-metal or polyatomic ion (anion).
For simple ionic compounds like \(\text{Li}_2\text{O}\), the name Lithium Oxide is formed by combining the names of Lithium (Li) and Oxygen (O). The 'ide' suffix is used for the anion.
For ionic compounds involving transition metals, we need to specify the metal's oxidation state. For \(\text{Cr(NO}_3\text{)}_2\), Chromium has a +2 oxidation state. Thus, it is named Chromium(II) Nitrate.
Following these guidelines, naming becomes straightforward. The metal's name comes first, followed by the anion with appropriate suffix or notation for the oxidation state.

Polyatomic Ions

Polyatomic ions are groups of atoms bonded together that carry a charge. These are crucial in naming and understanding ionic compounds.
Examples include \(\text{NO}_3^-\) (Nitrate) and \(\text{HCO}_3^-\) (Bicarbonate). Knowing common polyatomic ions helps in recognizing and naming compounds accurately.
In the given exercises, \(\text{Cr(NO}_3\text{)}_2\) includes the nitrate ion and is named Chromium(II) Nitrate. Similarly, \(\text{Mg(HCO}_3\text{)}_2\) involves the bicarbonate ion and is named Magnesium Bicarbonate.
The overall charge balance is achieved by ensuring that the total positive charge from the cations equals the total negative charge from the anions. This balance confirms the correct formulation and name of the compound.