Problem 25 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The compound which contains both ionic and covalent bonds is (a) \(\mathrm{CH}_{4}\) (b) \(\mathrm{H}_{2}\) (c) \(\mathrm{KCN}\) (d) \(\mathrm{KCl}\)

Step-by-Step Solution

Answer

The compound is \( \mathrm{KCN} \).

Step 1: Understanding the Question

We need to identify which compound among the given options contains both ionic and covalent bonds.

Step 2: Analyzing each Option

Let's examine each compound:- (a) \( \mathrm{CH}_4 \): Contains only covalent bonds between carbon and hydrogen.- (b) \( \mathrm{H}_2 \): Contains a single covalent bond between two hydrogen atoms.- (c) \( \mathrm{KCN} \): Contains an ionic bond between \( \mathrm{K}^+ \) and \( \mathrm{CN}^- \), and a covalent bond within the \( \mathrm{CN}^- \) ion itself.- (d) \( \mathrm{KCl} \): Contains an ionic bond between potassium and chlorine.

Step 3: Identifying Mixed Bond Types

Among the options, \( \mathrm{KCN} \) has both ionic and covalent bonds. The \( \mathrm{K^+} \) ion is ionically bonded to \( \mathrm{CN}^- \), while the \( \mathrm{CN}^- \) anion contains a covalent bond between carbon and nitrogen.

Step 4: Conclusion

The compound \( \mathrm{KCN} \) is the one that contains both ionic and covalent bonds as it has an ionic bond between K and CN and a covalent bond within CN.

Key Concepts

Ionic Bonds

Ionic bonds are formed when one atom transfers electrons to another atom. This usually happens between a metal and a non-metal. The metal atom donates electrons and becomes positively charged, known as a cation. Meanwhile, the non-metal atom accepts these electrons, becoming negatively charged, known as an anion.

The electrostatic attraction between the opposite charges of the cation and anion creates the ionic bond. The strength of this bond depends on the magnitude of charges and the distance between the charged particles.

Common examples of ionic compounds include sodium chloride (table salt) where sodium donates an electron to chlorine, forming a strong ionic lattice.

• Results from electron transfer
• Forms between metals and non-metals
• Creates charged ions

Covalent Bonds

Covalent bonds arise when atoms share pairs of electrons. This type of bond typically occurs between non-metal atoms, which have similar electronegativities. By sharing electrons, each participating atom achieves a more stable electron configuration, resembling the nearest noble gas.

There can be single, double, or even triple covalent bonds, depending on the number of electron pairs shared. A single bond shares one pair of electrons, a double bond shares two, and so on.

A common example is the molecule of water (H₂O), where the oxygen atom shares electrons with two hydrogen atoms.

• Involves sharing of electron pairs
• Occurs between non-metal atoms
• Can form single, double, or triple bonds

Mixed Bonds

Mixed bonds refer to compounds that contain both ionic and covalent bonds. An example of such a compound is potassium cyanide (KCN). In this ionic compound, the potassium (K) cation is ionically bonded to the cyanide (CN) anion.

Within the cyanide ion itself, carbon and nitrogen are covalently bonded by sharing electrons. Thus, the unique structure of KCN showcases both types of bonding: the ionic bond between potassium and the cyanide ion, and the covalent bond within the cyanide ion.

Mixed bonds are often found in compounds where a polyatomic ion forms part of the ionic lattice, allowing both bond types to coexist.

• Combines ionic and covalent bonds
• Example: Potassium cyanide (KCN)
• Polyatomic ions involved