The ions \(O_2^–\), \(F^–\), \(Na^+\), \(Mg^{2+}\) and \(Al^{3+}\) are isoelectronic. Their ionic radii show:
A significant increase from \(O_2^–\) to \(Al^{3+}\)
A significant decrease from \(O_2^–\) to \(Al^{3+}\)
An increase from \(O_2^–\) to \(F^–\) and then decrease from \(Na^+\) to \(Al^{3+}\)
- An decrease from \(O_2^–\) to \(F^–\) and then increase from \(Na^+\) to \(Al^{3+}\)
The Correct Option is B
Solution and Explanation
To determine the trend in ionic radii, let's analyze the situation:
Oxygen ion (\(O_2^–\)) has 10 electrons, fluorine ion (\(F^–\)) has 10 electrons, sodium ion (\(Na^+\)) has 10 electrons, magnesium ion (\(Mg^{2+}\)) has 10 electrons, and aluminum ion (\(Al^{3+}\)) has 10 electrons.
All these ions have the same number of electrons, so the main factor affecting their ionic radii will be the effective nuclear charge. The effective nuclear charge increases as you move across a period (from left to right) in the periodic table.
As you move from \(O_2^–\) to \(Al^{3+}\), you are going across the periodic table from left to right. This means that the effective nuclear charge is increasing, which generally leads to a decrease in ionic radii.
So, the correct option is (B): A significant decrease from \(O_2^–\) to \(Al^{3+}\)
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Concepts Used:
Trends in Periodic Table
The following trend in periodic properties of elements is observed:
Atomic size Trends:
The distance between the centre of the nucleus and the outermost shell of an atom is known as the atomic radius. In a group the atomic size increases due to the addition of shells as we move from one period to another. Across a period the atomic size decreases as the number of shells remain the same while the nuclear charge increases.
Metallic character Trends:
The elements which lose electrons to form cations are known as metals. Metallic character increases as we move down the group because the atomic size increases which lead to easy loss of electrons. On the other hand, it decreases across a period as we move from left to right.
Non-metallic character Trends:
The elements which have a tendency to gain electrons are known as non-metals. The tendency to gain electrons increases on moving across a period due to an increase in the nuclear charge and decrease in the atomic size. Hence, non-metallic character increases across a period.
Ionization potential Trends:
Ionization potential is defined as the amount of energy required to remove an electron from the outermost shell of a gaseous atom and convert it into a positively charged gaseous ion. The periodic properties in terms of ionization potential increase because the atomic size decreases across a period due to increase in the nuclear charge.
Melting Point Trends:
The melting point of an element is basically the energy required to change the state of an element from its solid state to its liquid state. Which essentially implies breaking a few bonds. Thus, higher the stronger the bond between the atoms, higher will be the melting point.