Problem 100 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following: List \(\mathbf{1}\) 1\. \(\mathrm{L}_{i}<\mathrm{Na}<\mathrm{K}<\mathrm{R} \mathrm{b}\) 5\. \(\mathrm{Li}<\mathrm{Be}>\mathrm{B}<\mathrm{C}\) 3\. \(\mathrm{F}_{2}>\mathrm{Cl}_{2}>\mathrm{Br}_{2}>\mathrm{I}_{2}\) 4\. \(\mathrm{F}_{2}>\mathrm{O}_{2}>\mathrm{Cl}_{2}>\mathrm{s}\) List II (i) increasing order energy (ii) decreasing order of metallic nature (iii) increasing order of size (iv) increasing order of electron affinity The correct matching is $$ \begin{array}{|c|c|c|c|c|} \hline & 1 & 2 & 3 & 4 \\ \hline a & \text { (i) } & \text { (iv) } & \text { (ii) } & \text { (iii) } \\\ \hline b & \text { (iii) } & \text { (i) } & \text { (iv) } & \text { (ii) } \\\ \hline \text { c } & \text { (iii) } & \text { (i) } & \text { (ii) } & \text { (iv) } \\ \hline \text { d } & \text { (i) } & \text { (ii) } & \text { (iii) } & \text { (iv) } \\ \hline \end{array} $$

Step-by-Step Solution

Answer

The correct option is 'c': 1(iii), 5(i), 3(ii), 4(iv).

Step 1: Analyze List 1, Item 1

For the sequence \(L_{i}< \mathrm{Na}< \mathrm{K}< Rb\), this is an increasing order of size for the elements in group 1 of the periodic table. As we move down the group, the atomic and ionic sizes increase. Therefore, this sequence relates to solution (iii) from List II, which is the increasing order of size.

Step 2: Analyze List 1, Item 5

In the sequence \( \mathrm{Li}< \mathrm{Be}> \mathrm{B}< \mathrm{C} \), we observe differences and comparisons in properties like ionization energy. Generally, beryllium has a higher ionization energy compared to lithium but follows a different order concerning boron and carbon. Thus, this sequence relates to solution (i) from List II, which is increasing order of ionization energy.

Step 3: Analyze List 1, Item 3

For the sequence \( \mathrm{F}_{2}> \mathrm{Cl}_{2}> \mathrm{Br}_{2}> \mathrm{I}_{2} \), fluorine has the highest tendency to gain electrons, indicating high electron affinity, followed by chlorine, bromine, and iodine. This sequence matches solution (iv) from List II, which is the increasing order of electron affinity.

Step 4: Analyze List 1, Item 4

The sequence \( \mathrm{F}_{2}> \mathrm{O}_{2}> \mathrm{Cl}_{2}> \mathrm{S} \) represents acids of strength or relative reactivity in a non-metal group. Fluorine's reactivity is higher followed by oxygen, chlorine, and sulfur, which can relate to the decreasing order of metallic nature, matching solution (ii) from List II.

Step 5: Determine Correct Matching Label

Matching the solutions with the appropriate List 1 item, the correct options are: a: 3 (ii): 5 (i): 1 (iii): 4 (iv). This corresponds to option 'c' in the provided table.

Key Concepts

Periodic Table Trends

The periodic table is a structured arrangement of elements ordered by increasing atomic number. One profound aspect of the periodic table is the trends that appear across and down the table. Understanding these trends aids in predicting and explaining the chemical behavior of elements.

When we move across a period from left to right, atomic size generally decreases due to an increase in the effective nuclear charge. Conversely, as you descend a group, atomic size increases because more electron shells are added, outweighing the effect of the increased nuclear charge.

• Atomic Radius: Decreases across a period, increases down a group.
• Ionization Energy: Generally increases across periods and decreases down groups.
• Electron Affinity: Often increases across periods with exceptions, and generally decreases down groups.
• Metallic Nature: Decreases across a period, increases down a group, reflecting the metallic characteristics of elements.

Predicting these trends not only supports understanding elemental reactivity but also aids in comprehending the periodic qualities that define each element's chemical behavior.

Ionization Energy

Ionization energy refers to the amount of energy required to remove an electron from an atom in its gaseous state. It's a pivotal concept because it indicates how strongly atoms hold onto their electrons.

This energy varies significantly across the periodic table. It tends to increase as one moves from left to right across a period because atoms on the right have more protons in their nucleus, leading to a stronger pull on the electrons. When analyzing items, for instance, Li < Be > B < C shows Be having higher ionization energy than Li as Be needs more energy to remove the electron due to its filled s sub-shell. However, anomalies occur due to varying sub-shell electron configurations.

• Trends: Often increases across a period, decreases down a group.
• Effect of Shielding: As electron shielding increases down a group, ionization energy decreases due to less effective nuclear attraction.

Ionization energy helps understand an element's reactivity, particularly regarding how easily atoms lose electrons to form positive ions.

Electron Affinity

Electron affinity is the measure of an atom's tendency to accept an electron, signifying how easily an atom can gain an electron. This property provides insight into how likely atoms in a material will react with other atoms by gaining electrons.

In the periodic table, electron affinity typically increases from left to right across a period, as seen in the sequence F₂ > Cl₂ > Br₂ > I₂. Here, fluorine has a high electron affinity despite some exceptions like its small size causing electron-electron repulsions. As one moves down a group, electron affinity decreases because additional electron levels cause outer electrons to be further from the nucleus.

• Trends: Increasing p-sublevel filling increases electron affinity.
• Exceptions: Elements like noble gases show negligible electron affinity due to stable electron configurations.

Understanding electron affinity is crucial in predicting how elements will engage in reactions involving electron exchange.

Metallic Nature

Metallic nature refers to the set of chemical properties typically associated with metals, including conductivity, malleability, and a tendency to lose electrons. The concept encompasses a broad range of behaviors that affect how elements participate in chemical reactions.

This property is stronger in elements located on the left side of the periodic table and decreases as you move rightwards. Conversely, metallic nature increases down a group.
Consider the sequence F₂ > O₂ > Cl₂ > S in terms of reactivity or decreasing metallic characteristics. Such positioning reflects how elements with metallic properties tend to lose electrons more readily, thus displaying a lesser reactivity when arranged correctly.

• Trends: Decreases across a period and increases down a group.
• Characterization: Metals tend to lose electrons easily due to lower ionization energies.

Understanding metallic nature helps anticipate the role elements play in forming alloys, conducting electricity, and reacting with other substances to form compounds.