Lanthanides are a series of chemical elements that consist of 15 metallic chemical elements with atomic numbers starting from 57 to 71 from lanthanum to lutetium. Actinide on the other hand encompasses 15 metallic chemical elements with atomic numbers beginning from 89 to 103 from actinium to lawrencium. Let us learn about the characteristics of lanthanides and actinides in periodic table:

The contraction of Lanthanides’ atomic size is its most prominent characteristics. This happens with the rise in atomic number and is known as lanthanide contraction. Moving along the lanthanides series from Ce (58) to Lu71, there is a fall in the atom’s size and rise in the atomic number. Lanthanide contraction occurs because of imperfect shielding of one 4f-electron that rises by one more in the same sub-shell.
The covalent and ionic radii are known to be the periodic characteristics. In periodic table the radii rises in a group from high to low as an orbit in added in a group for each step downwards. The covalent and ionic radii lowers in a period going from left to right since each new electron and proton raises the effective nuclear charge.

Actinides are highly electropositive. These are dense metals that have distinctive structures. Actinides react with dilute acid or boiling water to release hydrogen. These are all paramagnetic.
The lanthanides and actinides together form a group that is almost disconnected from the remaining periodic table. Also known as the inner transition series, this is said to be the f block of elements. This is owing to the numerical position amid Groups 2 and 3 of transition metals.

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