Anomalous Behavior of Lithium

Explanation:
Lithium, being the first element in Group 1 of the periodic table, exhibits some anomalous behavior compared to the other alkali metals. The correct reason for this anomalous behavior is the exceptionally small size of its atom.

Exceptionally Small Size of Lithium Atom
The size of an atom is determined by its atomic radius, which is the distance from the nucleus to the outermost electron. In general, atomic size increases as you move down a group in the periodic table due to the addition of new electron shells.

However, lithium has a smaller atomic radius compared to the other alkali metals in Group 1. This is because of the following reasons:

1. Effective Nuclear Charge: Lithium has a higher effective nuclear charge, which is the positive charge experienced by the outermost electrons. This is due to its low screening effect caused by the presence of only two inner shells.

2. Shielding Effect: The two inner shells in lithium do not effectively shield the outermost electron from the attraction of the nucleus. As a result, the outermost electron experiences a greater attractive force, pulling it closer to the nucleus and reducing the atomic radius.

3. Electron-Electron Repulsion: The two electrons in the inner shell repel the outermost electron, reducing its distance from the nucleus and hence, the atomic radius.

Consequences of Small Atomic Size

The small size of the lithium atom leads to several consequences, which can be considered as anomalous behavior when compared to the other alkali metals:

1. High Ionization Enthalpy: The ionization enthalpy of lithium is exceptionally high compared to the other alkali metals. This is because the outermost electron in lithium is closer to the nucleus and experiences a stronger attractive force. As a result, more energy is required to remove this electron.

2. Low Polarizing Power: The small size of the lithium ion makes it less polarizing compared to the larger alkali metal ions. Polarizing power refers to the ability of an ion to distort the electron cloud of another ion or molecule. Since lithium has a smaller size, its ability to polarize other ions or molecules is reduced.

3. High Degree of Hydration: Due to its small size, lithium ions have a high degree of hydration. Water molecules can effectively surround and solvate the lithium ions, leading to the formation of hydrated lithium compounds.

In conclusion, the exceptionally small size of the lithium atom is the correct reason for its anomalous behavior compared to the other alkali metals. This small size results in high ionization enthalpy, low polarizing power, and a high degree of hydration for lithium.