Problem 85 - Chemistry and Chemical Reactivity

Question

Which of the following pairs of elements are likely to form ionic compounds when allowed to react with each other? Write appropriate formulas for the ionic compounds you expect to form, and give the name of each. (a) chlorine and bromine (b) phosphorus and bromine (c) lithium and sulfur (d) indium and oxygen (e) sodium and argon (f) sulfur and bromine (g) calcium and fluorine

Step-by-Step Solution

Answer

(c) Li₂S - lithium sulfide; (d) In₂O₃ - indium(III) oxide; (g) CaF₂ - calcium fluoride.

Step 1: Understanding Ionic Compounds

Ionic compounds form between metals and non-metals through the transfer of electrons. The resulting compound is electrically neutral with cations and anions.

Step 1: Evaluating Pair (a) Chlorine and Bromine

Chlorine and bromine are both non-metals and form covalent bonds rather than ionic bonds. No ionic compound forms here.

Step 2: Evaluating Pair (b) Phosphorus and Bromine

Phosphorus and bromine are also non-metals, and they will form covalent bonds instead of ionic ones. Therefore, no ionic compound forms here.

Step 3: Evaluating Pair (c) Lithium and Sulfur

Lithium is a metal and sulfur is a non-metal. They can form an ionic compound. Lithium will lose one electron to form Li⁺ ions and sulfur will gain two electrons to form S²⁻ ions. The resulting compound is Li₂S (lithium sulfide).

Step 4: Evaluating Pair (d) Indium and Oxygen

Indium is a metal and oxygen is a non-metal. Indium typically forms In³⁺ ions and oxygen forms O²⁻ ions. Balancing the charges, we expect In₂O₃ as the ionic compound, called indium(III) oxide.

Step 5: Evaluating Pair (e) Sodium and Argon

Argon is a noble gas and does not readily form bonds due to its full valence shell (octet). Thus, no ionic compound is expected from sodium and argon.

Step 6: Evaluating Pair (f) Sulfur and Bromine

Both sulfur and bromine are non-metals and typically form covalent rather than ionic bonds. There is no ionic compound formed between them.

Step 7: Evaluating Pair (g) Calcium and Fluorine

Calcium is a metal and fluorine is a non-metal. Calcium loses two electrons to form Ca²⁺ and fluorine gains one electron to form F⁻. The resulting ionic compound is CaF₂, known as calcium fluoride.

Key Concepts

Electron Transfer

In the world of chemistry, understanding electron transfer is crucial when it comes to ionic compounds. Ionic compounds are formed when electrons are transferred from one atom to another. This electron transfer usually occurs between a metal and a non-metal.

Metals tend to lose electrons and non-metals tend to gain them. This transfer results in both atoms reaching a more stable electronic arrangement, often mimicking the electron configuration of the nearest noble gas. By losing electrons, metals become positively charged ions known as cations, while non-metals, by gaining these electrons, become negatively charged ions referred to as anions.

The electron transfer creates a strong electrostatic attraction between oppositely charged ions, leading them to form a stable ionic compound.

Cations and Anions

When elements undergo electron transfer, they become ions. Recognizing cations and anions is key to understanding ionic compounds.

Cations are positive ions that are typically formed by metal elements. Metals, such as lithium or calcium, lose electrons during chemical reactions, resulting in cations like Li⁺ or Ca²⁺. This loss provides them with a positive charge.

On the flip side, anions are negative ions formed generally by non-metals. Elements like sulfur or fluorine gain electrons to become negatively charged ions such as S²⁻ or F⁻. The formation of cations and anions is central to the structure and formation of ionic compounds, driving the interaction that results in their creation.

Metal and Non-Metal Reactions

Reactions between metals and non-metals are foundational to forming ionic compounds. When these two distinct types of elements interact, a reaction facilitated by their differing electron configurations occurs.

Metals, characterized by their tendency to lose electrons, and non-metals, which readily gain electrons, create an ideal partnership for ion formation. For example, when lithium (a metal) reacts with sulfur (a non-metal), lithium loses an electron and becomes a cation, whereas sulfur gains electrons to become an anion.

Through this process, they form a neutral ionic compound, such as lithium sulfide (Li₂S). This electron sharing provides stability, reflecting why these reactions are so common in chemistry.

Chemical Formulas

Understanding chemical formulas helps to recognize the composition of ionic compounds. These formulas represent the ratio of cations to anions in the compound, reflecting their charges and how they balance each other.

A chemical formula such as Li₂S means that there are two lithium cations for every one sulfur anion to balance their charges. Similarly, In₂O₃ indicates two indium cations, with a +3 charge each, balancing with three oxide anions, each with a -2 charge.

Chemical formulas are not just symbolic; they provide a clear representation of the substance's stability and composition, making it easier to understand how different elements combine to form ionic compounds.

Naming Ionic Compounds

Naming ionic compounds follows specific rules that help convey their composition clearly. The name usually starts with the cation followed by the anion. When naming these compounds, the metal's name remains unchanged, but the non-metal's name is altered to end in '-ide'.

For example, the ionic compound formed between calcium and fluorine is called calcium fluoride. In some cases, especially with transition metals, roman numerals indicate the metal's ionic charge due to the possibility of multiple charges. For example, In₂O₃ is referred to as indium(III) oxide, signaling that indium has a charge of +3.

Mastering these naming conventions allows for effective communication and understanding of the compounds' constituents and their resulting reactions.