Indium (In) Revision Guide

Atomic Model Details

Indium (In) is a chemical element with atomic number 49. It belongs to Group 13 (boron group) and Period 5 of the periodic table.

Atomic Number (Z): 49
- Number of Protons: 49
- Number of Electrons: 49 (in a neutral atom)
Mass Number (A): For the most abundant stable isotope, Indium-115 (¹¹⁵In), the mass number is 115.
- Number of Neutrons: 115 - 49 = 66
Atomic Size:
- Covalent Radius: 142 pm
- Metallic Radius: 167 pm

Electronic Configuration: [Kr] 4d¹⁰ 5s² 5p¹
- This configuration indicates that Indium has a filled d-subshell (4d¹⁰) and three valence electrons in its outermost shell (5s² 5p¹). The presence of the filled 4d subshell influences its properties.
Shell-wise Electron Distribution (Shell Diagram Representation):
- K-shell (n=1): 2 electrons
- L-shell (n=2): 8 electrons
- M-shell (n=3): 18 electrons
- N-shell (n=4): 18 electrons (4s², 4p⁶, 4d¹⁰)
- O-shell (n=5): 3 electrons (5s², 5p¹)
- Total electrons: 2 + 8 + 18 + 18 + 3 = 49

Indium’s position in Group 13 and Period 5 influences its periodic properties.

First Ionization Enthalpy (IE₁): 558.3 kJ/mol
- Trend: Ionization enthalpy generally decreases down Group 13. However, due to the poor shielding effect of the 4d electrons in elements like Gallium and Indium, the effective nuclear charge increases more than expected, leading to slight irregularities (e.g., Ga > Al, and Tl > In is observed due to lanthanoid contraction). Indium’s IE₁ is lower than Gallium’s but higher than Thallium’s.
Electronegativity (Pauling scale): 1.78
- Trend: Electronegativity generally decreases down a group due to increasing atomic size and shielding, which reduces the attraction for shared electrons.
Electron Gain Enthalpy (EGE): -28.9 kJ/mol
- Trend: For metallic elements, electron gain enthalpy values are generally small and often positive or slightly negative. Down the group, the tendency to accept an electron decreases, making EGE less negative (or more positive).
Atomic Radius:
- Covalent Radius: 142 pm
- Metallic Radius: 167 pm
- Trend: Atomic radius generally increases down Group 13 due to the addition of new electron shells. Indium’s radius is larger than Gallium’s and smaller than Thallium’s.