Question

Why there are 14 elements in actinidesactinides

Answer 1

Answer:

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Explanation:

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Answer 2

Explanation:

The lanthanide and actinide series make up the inner transition metals.

The lanthanide series includes elements 58 to 71, which fill their 4f sublevel progressively.

The actinides are elements 89 to 103 and fill their 5f sublevel progressively.

Actinides are typical metals and have properties of both the d-block and the f-block elements, but they are also radioactive.

Lanthanides have different chemistry from transition metals because their 4f orbitals are shielded from the atom’s environment.

Terms

lanthanide contractionThe progressive decrease in the radii of atoms of the lanthanide elements as the atomic number increases; evident in various physical properties of the elements and their compounds.

lanthanideAny of the 14 rare earth elements from lanthanum to lutetium in the periodic table. Because their outermost orbitals are empty, they have very similar chemistry. Below them are the actinides.

actinideAny of the 14 radioactive elements of the periodic table that are positioned under the lanthanides, with which they share similar chemistry.

The lanthanides and actinides form a group that appears almost disconnected from the rest of the periodic table. This is the f block of elements, known as the inner transition series. This is due to the proper numerical position between Groups 2 and 3 of the transition metals.

The chemistry of the lanthanides differs from main group elements and transition metals because of the nature of the 4f orbitals. These orbitals are “buried” inside the atom and are shielded from the atom’s environment by the 4d and 5p electrons. As a consequence, the chemistry of the elements is largely determined by their size, which decreases gradually with increasing atomic number. This phenomenon is known as the lanthanide contraction. All the lanthanide elements exhibit the oxidation state +3.

Actinides are typical metals. All of them are soft, have a silvery color (but tarnish in air), and have relatively high density and plasticity. Some of them can be cut with a knife. The hardness of thorium is similar to that of soft steel, so heated pure thorium can be rolled in sheets and pulled into wire. Thorium is nearly half as dense as uranium and plutonium but is harder than both of them.

Unlike the lanthanides, most elements of the actinide series have the same properties as the d block. Members of the actinide series can lose multiple electrons to form a variety of different ions. All actinides are radioactive, paramagnetic, and, with the exception of actinium, have several crystalline phases. All actinides are pyrophoric, especially when finely divided (i.e., they spontaneously ignite upon exposure to air).

The melting point of actinides does not have a clear dependence on the number of f electrons. The unusually low melting point of neptunium and plutonium (~640 °C) is explained by hybridization of 5f and 6d orbitals and the formation of directional bonds in these metals. Like the lanthanides, all actinides are highly reactive with halogens and chalcogens; however, the actinides react more easily. Actinides, especially those with a small number of 5f electrons, are prone to hybridization. This is explained by the similarity of the electron energies at the 5f, 7s, and 6d subshells. Most actinides exhibit a larger variety of valence states

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