Question

For which of the following elements would the most common ion be expected to have a larger radius than that of its corresponding atom?
1. Cl
2. Na
3. Cu
4. Sr

Answer 1

Answer: The ion that is expected to have a larger radius than the corresponding atom is chlorine.

Explanation:

There are two types of ions:

• Cations: They are formed when an atom looses its valence electrons. They are positive ions.
• Anions: They are formed when an atom gain electrons in its outermost shell. They are negative ions.

For positive ions, the removal of electron increases the nuclear charge for an outermost electron because the outermost electrons are more strongly attracted by the nucleus. So, the effective nuclear charge increases for cations and thus, the size of the cation will be smaller than that of the corresponding atom.

For negative ions, the addition of electron decreases the nuclear charge for an outermost electron because the outermost electrons are less strongly attracted by the nucleus. So, the effective nuclear charge decreases for anions and thus, the size of the anion will be larger than that of the corresponding atom.

For the given options:

Option a: Chlorine

Chlorine gains 1 electron and form $Cl^-$ ion

Option b: Sodium

Sodium looses 1 electron and form $Na^+$ ion

Option c: Copper

Copper looses 2 electrons and form $Cu^{2+}$ ion

Option d: Strontium

Strontium looses 2 electrons and form $Sr^{2+}$ ion

Hence, the ion that is expected to have a larger radius than the corresponding atom is chlorine.