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Question
The reason behind the smaller atomic radius of Ga as compared to Al is ?
The reason behind the smaller atomic radius of Ga as compared to Al is ?
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Solution
The correct option is A poor screening effect of 3d electrons
The presence of an additional 10 d-electrons in Ga offers a poor screening effect for the outer electrons which increases the force of attraction between the outermost electrons and nuclear charge, due to which the atomic radius of gallium decreases.
Hence, Ga has a lower atomic radius as compared to Al. The atomic radius of Ga (135 pm) is less than that of Al (143 pm).
Theory
Atomic & Ionic Radii:
Down the group, for each successive member, one extra shell of electrons is added. Atomic radius increases.
The presence of an additional 10 d-electrons in Ga offers a poor screening effect for the outer electrons which increases the force of attraction between the outermost electrons and nuclear charge, due to which the atomic radius of gallium decreases.
Hence, Ga has a lower atomic radius as compared to Al. The atomic radius of Ga (135 pm) is less than that of Al (143 pm).
Electronegativity:
Down the group, electronegativity first decreases from B to Al and then increases marginally due to the discrepancies in the atomic size of the elements.
Ionization Enthalpy:
The sum of the first three ionization enthalpies for each of the elements is very high.
Irregular trends in the I.E. values are observed between Al and Ga and between In and Tl due to the poor shielding effect of d and f orbitals.
Physical Properties:
B is non-metallic in nature.
It is an extremely hard and black-coloured solid.
It exists in many allotropic forms.
B has an unusually high melting point due to very strong crystalline lattice.
The rest of the members are soft metals with low melting points and high electrical conductivities.
Ga which has a lower melting point (303K), could exist in a liquid state during summer.
The density of the elements increases down the group from boron to thallium.
The presence of an additional 10 d-electrons in Ga offers a poor screening effect for the outer electrons which increases the force of attraction between the outermost electrons and nuclear charge, due to which the atomic radius of gallium decreases.
Hence, Ga has a lower atomic radius as compared to Al. The atomic radius of Ga (135 pm) is less than that of Al (143 pm).
Theory
Atomic & Ionic Radii:
Down the group, for each successive member, one extra shell of electrons is added. Atomic radius increases.
The presence of an additional 10 d-electrons in Ga offers a poor screening effect for the outer electrons which increases the force of attraction between the outermost electrons and nuclear charge, due to which the atomic radius of gallium decreases.
Hence, Ga has a lower atomic radius as compared to Al. The atomic radius of Ga (135 pm) is less than that of Al (143 pm).
Electronegativity:
Down the group, electronegativity first decreases from B to Al and then increases marginally due to the discrepancies in the atomic size of the elements.
Ionization Enthalpy:
The sum of the first three ionization enthalpies for each of the elements is very high.
Irregular trends in the I.E. values are observed between Al and Ga and between In and Tl due to the poor shielding effect of d and f orbitals.
Physical Properties:
B is non-metallic in nature.
It is an extremely hard and black-coloured solid.
It exists in many allotropic forms.
B has an unusually high melting point due to very strong crystalline lattice.
The rest of the members are soft metals with low melting points and high electrical conductivities.
Ga which has a lower melting point (303K), could exist in a liquid state during summer.
The density of the elements increases down the group from boron to thallium.
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