Problem 44 - A Complete Resource Book in Chemistry for JEE Main

Question

The basic character of the transition metal monoxides follow the order (a) \(\mathrm{CrO}>\mathrm{VO}>\mathrm{Feo}>\mathrm{TiO}\) (b) \(\mathrm{TiO}>\mathrm{VO}>\mathrm{CrO}>\mathrm{FeO}\) (c) \(\mathrm{TiO}>\mathrm{FeO}>\mathrm{VO}>\mathrm{CrO}\) (d) \(\mathrm{VO}>\mathrm{CrO}>\mathrm{TiO}>\mathrm{FeO}\)

Step-by-Step Solution

Answer

(b) \(\mathrm{TiO} > \mathrm{VO} > \mathrm{CrO} > \mathrm{FeO}\)

Step 1: Understand the Concept of Basicity in Metal Oxides

The basic character of a metal oxide is related to the metallic character of the element. The more metallic an element is, the more basic its oxide will be. Transition metals tend to have metal oxides that range from basic to amphoteric or acidic as their oxidation state increases.

Step 2: Identify the Oxidation States

For the given oxides: \(\mathrm{TiO}\) has Ti in +2 state, \(\mathrm{VO}\) has V in +2 state, \(\mathrm{CrO}\) has Cr in +2 state, and \(\mathrm{FeO}\) has Fe in +2 state.

Step 3: Compare Metallic Character

In the periodic table, moving across the d-block from left to right, the metallic character generally decreases. Thus, from Ti to Fe, the metallic character decreases because Ti is more to the left on the periodic table compared to Fe.

Step 4: Predict the Basicity Order

Given that the metallic character decreases from Ti to Fe, the basic character of their monoxides will decrease in the same order. Therefore, the order from most basic to least basic would be \(\mathrm{TiO} > \mathrm{VO} > \mathrm{CrO} > \mathrm{FeO}\).

Step 5: Choose the Correct Answer

From the predicted basicity order, it aligns with option (b): \(\mathrm{TiO} > \mathrm{VO} > \mathrm{CrO} > \mathrm{FeO}\).

Key Concepts

Basic Character

Basic character refers to the tendency of a substance to react with acids and form salts and water. When we talk about the basic character of metal oxides, it often relates to how these oxides interact with acidic substances. Transition metal oxides exhibit different levels of basicity. This characteristic is intricately linked to the metallic character of the metal itself.
Generally, metal oxides of more metallic elements show higher basicity. Hence, a stronger metallic character will result in stronger basic oxides. This is because highly metallic elements tend to release their electrons readily, forming positive ions that can easily bond with negative ions from acids. Therefore, as we look at monoxides of transition metals like \(TeO\), \(VO\), \(CrO\), and \(FeO\), their basic character decreases as their position in the periodic table moves from left to right, reflecting the decrease in metallic character.

Metallic Character

The metallic character of an element describes its physical and chemical properties associated with metals. Characteristics include

• Good conductors of heat and electricity
• Malleability (ability to be hammered into sheets)
• Ductility (ability to be drawn into wires)
• Tendency to lose electrons and form positive ions

As we move across the periodic table, specifically across the transition metals in the d-block, the metallic character typically decreases. For the metals in our example, \(Ti\) is positioned to the far left of these transition metals, and thus it possesses the highest metallic character. Following the trend to the right, \(V\), \(Cr\), and finally \(Fe\) follow, with \(Fe\) exhibiting the least metallic character among them. This decrease in metallic character affects how their oxides behave in terms of basicity, explaining why \(TiO\) (with high metallic character) is more basic compared to \(FeO\).

Oxidation States

Oxidation states are a way of keeping track of electrons in atoms participating in chemical bonds. In simple terms, it represents the charge an atom would have if all the bonds were purely ionic. Transition metal oxides can exhibit a range of oxidation states due to their ability to lose different numbers of electrons.
In the context of the transition metal monoxides in question, each metal ( Ti, V, Cr, and Fe) is in the +2 oxidation state. This means that each metal has lost two electrons. Having the same oxidation state simplifies our comparison of their metallic and basic characteristics, as it removes the variable of differing electron loss. The uniformity in oxidation states across these metals helps highlight the impact their intrinsic metallic character has on the basicity of their oxides.

Periodicity in Chemistry

Periodicity refers to the repeating patterns of chemical and physical properties of elements as observed across different periods and groups in the periodic table. These trends include atomic size, electronegativity, ionization energy, and metallic character, among others.
As we move from left to right across a period in the transition elements, specifically across the d-block which contains our metals of interest ( Ti, V, Cr, and Fe), there is a general decrease in metallic character. Correspondingly, there is also a decrease in the basicity of their oxides. This periodic trend allows us to predict the relative properties of these elements and their compounds.

• Moving from left to right, atomic size generally decreases
• Electronegativity and ionization energy typically increase
• Thus, elements become less metallic

Understanding these trends helps to explain the variation in basicity among the transition metal monoxides discussed.