Question

Classify each compound as ionic or molecular. If it is ionic, determine whether the metal forms only one type of ion or more than one type of ion. (a) \(\mathrm{KCl}\) (b) \(\mathrm{CBr}_{4}\) (c) \(\mathrm{NO}_{2}\) (d) \(\mathrm{Sn}\left(\mathrm{SO}_{4}\right)_{2}\)

Short answer

(a) KCl is ionic, one type of ion (K+); (b) CBr4 is molecular; (c) NO2 is molecular; (d) Sn(SO4)2 is ionic, more than one type of ion (Sn2+ and Sn4+).

Step-by-step solution

Identification of Compound Type for KCl

Determine if the compound KCl is ionic or molecular. Potassium (K) is a metal and chlorine (Cl) is a nonmetal. Compounds formed between metals and nonmetals are ionic, so KCl is classified as an ionic compound. Potassium forms only one type of cation, K+, so it forms only one type of ion.

Identification of Compound Type for CBr4

Determine if the compound CBr4 is ionic or molecular. Carbon (C) and bromine (Br) are both nonmetals. Compounds formed between nonmetals are molecular, so CBr4 is classified as a molecular compound.

Identification of Compound Type for NO2

Determine if the compound NO2 is ionic or molecular. Both nitrogen (N) and oxygen (O) are nonmetals. Compounds formed between nonmetals are molecular, so NO2 is classified as a molecular compound.

Identification of Compound Type for Sn(SO4)2

Determine if the compound Sn(SO4)2 is ionic or molecular. Tin (Sn) is a metal, and the sulfate ion (SO4)2- is a polyatomic ion. Compounds formed between metals and polyatomic ions are ionic, so Sn(SO4)2 is classified as an ionic compound. Tin can form more than one type of cation, like Sn2+ and Sn4+, so it forms more than one type of ion.

Key concepts

Compound Classification

Understanding the classification of compounds is a crucial step in chemistry, as it helps to predict the properties and the behavior of substances. Compounds are broadly divided into two main categories: ionic and molecular (also known as covalent).

Ionic compounds are formed when metals transfer electrons to nonmetals, resulting in the creation of positive and negative ions that attract each other due to opposite charges. A classic example is table salt, KCl or Potassium Chloride, where Potassium gives up an electron to the Chlorine atom, forming a sturdy lattice of oppositely charged ions.
On the other hand, molecular compounds involve nonmetals sharing electrons, producing molecules instead of ion networks. An example would be carbon tetrabromide, CBr_{4}, where carbon and bromine atoms share electrons.

Identifying the nature of the compound provides a foundation for understanding its physical and chemical properties, such as melting and boiling points, solubility, and conductivity.

Ion Formation

Ion formation is a fundamental chemical process where atoms gain or lose electrons to obtain a full outer electron shell, leading to more stable electronic configurations. Metals tend to lose electrons and form positively charged ions called cations. Nonmetals usually gain electrons and become negatively charged ions, known as anions.

For example, in an ionic compound such as KCl, the metal potassium (K) loses one electron to form a K+ ion. This process is essential in the creation of an ionic bond with the chloride ion (Cl-), which has accepted the electron. This electron transfer allows both ions to achieve the electron configuration of noble gases, which is a driving factor behind the formation of ions.

Metal and Nonmetal Compounds

The difference between metal and nonmetal compounds lies in the way they bond and the type of elements involved. When a metal and a nonmetal react, such as tin (Sn) and sulfate (SO_{4}^{2-}), they form an ionic compound. Metals like Sn can vary in the charge of the ions they form, which explains why tin can produce ions with different charges, such as Sn^{2+} and Sn^{4+}.

The Bonding in Ionic Compounds

Ionic bonding occurs because metals have few electrons in their outermost shell and are able to lose them easily, while nonmetals have more electrons and tend to gain them to fill their outer shell. The metal becomes a positively charged cation, while the nonmetal becomes a negatively charged anion, and they attract each other to form a stable ionic compound. Tin(IV) sulfate, Sn(SO_{4})_{2}, serves as an excellent example, where tin interacts with the polyatomic sulfate ion to form an ionic substance.

Polyatomic Ions

Polyatomic ions are charged entities composed of two or more covalently bonded atoms that function as a single ion. They can be either positively or negatively charged. Unlike simple ions which consist of a single atom, polyatomic ions consist of a group of atoms that exhibit a charge due to the loss or gain of electrons.

Pride of place among polyatomic ions is taken by those like the sulfate ion (SO_{4}^{2-}), which has a central sulfur atom surrounded by four oxygen atoms in a tetrahedral arrangement. These complex ions behave as a unit in a chemical reaction, often combining with metal ions to form ionic compounds. Sulfate, for example, joins with tin (II) or tin (IV) ions to create compounds such as SnSO_{4} or Sn(SO_{4})_{2}, respectively, showcasing their versatility in forming stable structures with various metals.