Chemistry Q71 – NEET-UG 2023

Home Chemistry Periodicity & ElementsQuestion #526

The element expected to form largest ion to achieve the nearest noble gas configuration is :

Clue 1 of 3: Noble Gas Configuration

Elements form ions to achieve a stable electron configuration, typically that of the nearest noble gas.

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Ninja Strategy•Isoelectronic Series Trend

Recognize that all ions will be isoelectronic with Neon, and then apply the trend that ionic size decreases with increasing nuclear charge for isoelectronic species.

🧠 Full Solution Path

Step 1: Determine the ions formed by each element✦ Active

To achieve the nearest noble gas configuration (Neon, with 10 electrons), the given elements will form the following ions: - Nitrogen (N, atomic number $Z = 7$ ) gains 3 electrons to form $N^{3 -}$ (10 electrons). - Oxygen (O, atomic number $Z = 8$ ) gains 2 electrons to form $O^{2 -}$ (10 electrons). - Fluorine (F, atomic number $Z = 9$ ) gains 1 electron to form $F^{-}$ (10 electrons). - Sodium (Na, atomic number $Z = 11$ ) loses 1 electron to form $N a^{+}$ (10 electrons). All these ions ( $N^{3 -}$ , $O^{2 -}$ , $F^{-}$ , $N a^{+}$ ) are isoelectronic species, meaning they have the same number of electrons (10 electrons).

Step 2: Apply the rule for ionic radii of isoelectronic species○ Expand

For isoelectronic species, the ionic radius is inversely proportional to the nuclear charge (atomic number). This means that as the nuclear charge increases, the electrons are pulled more strongly towards the nucleus, resulting in a smaller ionic size.

Step 3: Compare the ionic sizes○ Expand

The atomic numbers ( $Z$ ) of the elements are: - N: $Z = 7$ - O: $Z = 8$ - F: $Z = 9$ - Na: $Z = 11$ Since ionic size decreases with increasing nuclear charge for isoelectronic species, the order of ionic radii (from largest to smallest) will be: $N^{3 -} > O^{2 -} > F^{-} > N a^{+}$ Therefore, Nitrogen forms the largest ion ( $N^{3 -}$ ).

💡 Teacher's Secret Hint

Remember that anions are generally larger than cations when comparing isoelectronic species, and within anions, the one with the lowest nuclear charge is the largest.

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Chemistry Question 71 – NEET-UG 2023

Clue 1 of 3: Noble Gas Configuration

🧠 Full Solution Path