The regular decrease in the size of lanthanide ions from its first element to the last element is known as lanthanide contraction. It is due to greater effect of the increased nuclear charge than that of the screening effect. The same effect is exhibited by d block elements. Cause of the d-block contraction is the poor shielding of the nuclear charge by the electrons in the d orbitals. The outer valence electrons are more strongly attracted by the nucleus causing the observed increase in ionization potentials.

The cause of the d-block contraction is the poor shielding of the nuclear charge by the electrons in the dorbitals. ... The d-block contractioncan be compared to the lanthanidecontraction which is caused by inadequate shielding of nuclear charge by electrons occupying f orbitals.

D-Block Contraction and F-Block Contraction

D-block contraction and f-block contraction are two important concepts in the field of chemistry that explain the periodic trends of atomic radii within transition metals and inner transition metals, respectively. These contractions occur due to the poor shielding effect of the d and f electrons, resulting in smaller atomic radii for the elements in these blocks compared to what would be expected based on their position in the periodic table.

D-Block Contraction:
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The d-block contraction refers to the decrease in atomic radii across the transition metals series. This contraction occurs because the additional d-electrons in each successive element do not effectively shield the increased nuclear charge from the outermost electrons. As a result, the atomic radii decrease across the d-block.

Key Points:
1. Poor shielding effect: The d-electrons, being closer to the nucleus, are not as effective in shielding the increased nuclear charge from the outermost electrons.
2. Decreased atomic radii: The decreased shielding leads to an increased effective nuclear charge, pulling the outermost electrons closer to the nucleus and resulting in smaller atomic radii.
3. Consequences: The d-block contraction affects various properties such as ionization energy, electronegativity, and the formation of chemical bonds within the transition metals.

F-Block Contraction:
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The f-block contraction, also known as the lanthanide contraction, occurs in the inner transition metals of the f-block. It is similar to the d-block contraction but is observed for the elements in the f-orbital series. The f-electrons, being poorly shielded, do not effectively counterbalance the increasing nuclear charge, leading to a decrease in atomic radii across the f-block.

Key Points:
1. Poor shielding effect: The f-electrons, being deeply embedded within the atom, provide poor shielding against the increasing nuclear charge.
2. Decreased atomic radii: Similar to the d-block contraction, the f-block contraction results in smaller atomic radii due to the increased effective nuclear charge pulling the outermost electrons closer to the nucleus.
3. Lanthanide contraction: The f-block contraction is also referred to as the lanthanide contraction because it is specifically observed in the lanthanide series of elements.
4. Consequences: The f-block contraction impacts various properties such as ionization energy, electronegativity, and the formation of chemical bonds within the inner transition metals.

In summary, both the d-block contraction and f-block contraction occur due to the poor shielding effect of the d and f electrons, respectively. These contractions result in smaller atomic radii for the elements in these blocks, affecting their chemical and physical properties.