Problem 5 - A Complete Resource Book in Chemistry for JEE Main

Question

Cation and anion combines in a crystal to form following type of compound. (a) ionic (b) metallic (c) covalent (d) dipole-dipole

Step-by-Step Solution

Answer

An ionic compound is formed.

Step 1: Identify the Components Involved

The exercise involves cations and anions combining to form a crystal. A cation is a positively charged ion, while an anion is a negatively charged ion.

Step 2: Understand the Nature of the Chemical Bond

Cations and anions are attracted to each other due to their opposite charges. This electrostatic attraction forms a bond between them.

Step 3: Determine the Type of Compound Formed

Crystal lattices formed by electrostatic attractions between cations and anions are referred to as ionic bonds. Compounds formed with these bonds are known as ionic compounds.

Step 4: Evaluate the Given Options

Among the options provided: (a) ionic refers to compounds formed by cations and anions, (b) metallic involves metal atoms sharing electrons, (c) covalent involves sharing of electron pairs between atoms, and (d) dipole-dipole is a type of intermolecular force. Therefore, the correct option is (a) ionic.

Key Concepts

Cations and Anions

In chemistry, understanding the nature of cations and anions is crucial for grasping how ionic compounds are formed. Cations are positively charged ions, which means they have more protons than electrons. This positive charge usually arises when an atom loses one or more electrons. On the other hand, anions are negatively charged ions. They have more electrons than protons, typically resulting from an atom gaining electrons to achieve a more stable electron configuration.

When you combine cations and anions, you have the basic recipe for creating an ionic compound. The process of forming these ions often involves electron transfer. For example, a common scenario is the transfer of electrons from a metal atom (forming a cation) to a non-metal atom (forming an anion). This electron transfer is what leads to the charged ions interacting strongly to form ionic compounds.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in compounds. In the case of ionic compounds, we primarily focus on ionic bonds, which are formed through the transfer of electrons from one atom to another. This electron transfer results in the creation of cations and anions.

• Ionic bonds occur between metals and non-metals.
• In these bonds, metals lose electrons to form positive ions, while non-metals gain those electrons to form negative ions.
• The fully formed ionic bonds are typically strong due to the significant charges.
  

Thus, ionic bonds form because metals tend to donate electrons and non-metals tend to accept them to achieve stable electron configurations. This exchange creates a strong bond due to the resulting opposite charges.

Electrostatic Attraction

Electrostatic attraction is the driving force behind the formation of ionic compounds. Once cations and anions are formed through the transfer of electrons, they are naturally attracted to each other due to their opposite charges. This attraction is strong and direct, leading to the formation of a stable ionic bond.

• The magnitude of this attraction depends on the charge and size of the ions involved. Larger charges and smaller ions typically lead to stronger attractions.
• This electrostatic force is what binds the ions together in a fixed position within the crystal lattice of the ionic compound.
  

In summary, electrostatic attraction is a non-contact force that is essential for the cohesion of ionic compounds, holding the ions tightly in specific arrangements.

Crystal Lattice

A crystal lattice is the regular and repeating three-dimensional arrangement of ions in an ionic compound. When cations and anions attract each other, they form a highly structured network known as a crystal lattice.

• This lattice is important because it helps to minimize the potential energy of the compound and increase its stability.
• The strength and physical properties of ionic compounds, such as high melting and boiling points, are due to their lattice structures.
  

The entire structure is maintained through electrostatic attraction between oppositely charged ions. The strength of the lattice depends on the size and charge of the ions: smaller, highly charged ions create stronger lattices. In essence, the crystal lattice not only holds the compound together but also defines many of its physical properties.