Problem 119 - A Complete Resource Book in Chemistry for JEE Main

Question

Properties that are directly or indirectly related to the electronic configuration of the elements and show a regular gradation when we move from left to right in a period or form top to bottom in a group are called periodic properties. Some of these properties are ionization energy, electron affinity and electronegativity Which of the following is arranged in the order of decreasing electropositive character? (a) \(\mathrm{Fe}, \mathrm{Mg}, \mathrm{Cu}\) (b) \(\mathrm{Mg}, \mathrm{Cu}, \mathrm{Fe}\) (c) \(\mathrm{Mg}, \mathrm{Fe}, \mathrm{Cu}\) (d) \(\mathrm{Cu}, \mathrm{Fe}, \mathrm{Mg}\)

Step-by-Step Solution

Answer

The correct answer is (c) \( \mathrm{Mg}, \mathrm{Fe}, \mathrm{Cu} \).

Step 1: Define Electropositive Character

The electropositive character of an element refers to its tendency to lose electrons and form positive ions. Elements that are more electropositive are typically metals and are more likely to give up electrons to form cations.

Step 2: Arrange Elements by Metallicity

In general, the electropositive character increases down a group and decreases across a period from left to right. Among \( \mathrm{Fe} \), \( \mathrm{Mg} \), and \( \mathrm{Cu} \), magnesium (Mg) is an alkaline earth metal and is more electropositive compared to the transition metals iron (Fe) and copper (Cu).

Step 3: Compare Electropositive Characters

Considering periodic trends, \( \mathrm{Mg} \) is more electropositive than both \( \mathrm{Fe} \) and \( \mathrm{Cu} \), as it is further to the left in the period table. Between \( \mathrm{Fe} \) and \( \mathrm{Cu} \), iron (Fe) is more electropositive than copper (Cu) because iron is less noble and thus more willing to lose its electrons compared to copper.

Step 4: Determine Correct Order

By comparing these elements based on their metallic character, the order based on decreasing electropositive character should be \([ \mathrm{Mg}, \mathrm{Fe}, \mathrm{Cu} ]\).

Key Concepts

Electropositive Character

Electropositive character, also known as metallic character, refers to an element's ability to lose electrons and form positive ions, or cations. This property is common in metals, which readily give up electrons during chemical reactions. Generally, electropositive character increases as you move down a group in the periodic table due to larger atomic radii and loosely held outer electrons.
For example, when comparing magnesium (Mg), iron (Fe), and copper (Cu), magnesium is the most electropositive. As an alkaline earth metal, it sits further to the left on the periodic table, indicating a stronger tendency to lose electrons. This aligns with the periodic trend where electropositive character decreases from left to right within a period.

Electronegativity

Electronegativity describes an atom's tendency to attract and hold onto electrons in a chemical bond. It is essentially the opposite of electropositive character. Elements with high electronegativity tend to hold onto their electrons tightly and often gain electrons in reactions, forming negative ions or anions.
Moving across a period from left to right, electronegativity generally increases, while it decreases as you go down a group. This is because atoms with smaller radii have a stronger pull on their valence electrons. Non-metals, like fluorine and oxygen, are typically more electronegative than metals, influencing their chemical behavior profoundly.

Ionization Energy

Ionization energy is the energy required to remove an electron from an atom in its gaseous state. The first ionization energy refers to the energy needed to remove the first electron, while subsequent ionization energies involve removing additional electrons.
There is a clear trend with ionization energy in the periodic table: it increases across a period due to stronger nuclear charge attracting electrons more tightly, and it decreases down a group as outer electrons are further from the nucleus and experience less electrostatic pull. This concept is crucial in understanding reactivity; elements with low ionization energy (typically metals) lose electrons easily, thus being more reactive cation-formers.

Electron Affinity

Electron affinity measures the energy change when an electron is added to a neutral atom, forming a negative ion. It reflects how much an atom wants to gain an electron. Elements with high electron affinity, like halogens, release significant energy upon gaining an electron due to the high stability of the resulting negative ion.
Generally, electron affinity becomes more negative across a period, implying a stronger desire to gain electrons, while it usually becomes less negative moving down a group. Elements where the added electron results in a half-filled or fully filled p-orbital structure tend to have higher electron affinity due to increased electron configuration stability. This detail helps explain the high reactivity of the nonmetals as they pursue stable electron arrangements.