Problem 133 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of pairs of elements which show diagonal relationship across the periodic table is \(. \mathrm{Li}-\mathrm{Mg}\); \(\mathrm{Be}-\mathrm{Al} ; \mathrm{B}-\mathrm{Si} ; \mathrm{K}-\mathrm{Sr} ; \mathrm{N}-\mathrm{S} ; \mathrm{Na}-\mathrm{Ca}\)

Step-by-Step Solution

Answer

There are 3 pairs that show a diagonal relationship: Li-Mg, Be-Al, and B-Si.

Step 1: Understanding the Concept of Diagonal Relationship

Elements show a diagonal relationship in the periodic table where elements with similar properties are positioned diagonally from each other. Typically, this occurs with elements in adjacent groups and periods, like from the second period to the third and from the third group to a subsequent group, such as lithium to magnesium.

Step 2: Identify Diagonal Pairs in the Given List

Review the given pairs to see which pairs exhibit a diagonal relationship. The pairs are: 1. Li-Mg 2. Be-Al 3. B-Si 4. K-Sr 5. N-S 6. Na-Ca. The typical diagonal relationships occur between the second and third periods such as Li-Mg and Be-Al.

Step 3: Check Each Pair for Diagonal Relationship

Examine each pair given to ensure they follow the periodic trend of diagonal relationship: - Li-Mg: yes, Li (Group 1, Period 2) and Mg (Group 2, Period 3). - Be-Al: yes, Be (Group 2, Period 2) and Al (Group 13, Period 3). - B-Si: yes, B (Group 13, Period 2) and Si (Group 14, Period 3). - K-Sr: no, K (Group 1, Period 4) and Sr (Group 2, Period 5). - N-S: no, N (Group 15, Period 2) and S (Group 16, Period 3). - Na-Ca: no, Na (Group 1, Period 3) and Ca (Group 2, Period 4).

Step 4: Count the Valid Diagonal Relationships

After checking, the valid pairs showing diagonal relationships are: - Li-Mg - Be-Al - B-Si This makes a total of 3 pairs.

Key Concepts

Periodic Table

The periodic table is a powerful tool in chemistry that organizes all known elements according to atomic number, electron configuration, and repeating chemical properties. It acts as a map, enabling scientists and students alike to predict the characteristics and behaviors of elements.

• **Groups:** Vertical columns in the periodic table, where elements typically have similar valence electron configurations and chemical properties.
• **Periods:** Horizontal rows, where elements have the same number of atomic orbitals.

The periodic table's design reveals a fascinating pattern: elements become more metallic as you move from right to left and top to bottom. Non-metallic properties are generally on the right top side. This arrangement allows the periodic table to display the elements so that periodic trends, such as electronegativity, ionization energy, and atomic radius, can be easily visualized. The diagonal relationship is one such pattern that reveals how elements with similar properties often appear diagonally across the table.

Diagonal Pairs

Diagonal pairs in the periodic table highlight the diagonal relationship between elements. This relationship is a unique chemistry concept where certain elements in adjacent groups and periods exhibit similar properties.

• **Li-Mg:** Lithium is in Group 1, Period 2, while Magnesium is in Group 2, Period 3.
• **Be-Al:** Beryllium in Group 2, Period 2, pairs diagonally with Aluminum in Group 13, Period 3.
• **B-Si:** Boron in Group 13, Period 2, has a diagonal relationship with Silicon in Group 14, Period 3.

These diagonal relationships are observed primarily between elements in the s and p blocks of the periodic table, where they share certain chemical behaviors, such as forming oxides and having comparable electronegativity and ionization energies. For instance, lithium (Li) and magnesium (Mg) can both form stable oxides and react in similar ways with water under controlled conditions.

Element Properties

The properties of elements in the periodic table are influenced significantly by their electron configurations and position within the table. Elements with a diagonal relationship often share specific properties.

• **Metallic Character:** Diagonal elements may have similar metallic properties, despite being in different groups. For example, Lithium and Magnesium can both act like metals.
• **Reactivity:** Elements like Beryllium and Aluminum exhibit comparable reactivity with non-metals, forming oxides and other compounds easily.
• **Electronegativity and Ionization Energy:** These two properties often correlate for diagonal pairs, reflecting a balance in their attraction for electrons.

Understanding these shared properties helps chemists predict the behavior of unknown compounds, facilitating advancements in chemical reactions and material science. A clear grasp of these characteristics can aid in predicting how elements might interact in novel or unexpected ways, echoing the predictive wisdom of the periodic table itself.