Question

In any group second period elements exhibit anomalous properties. Correct statements about this is/are:

A) Generally maximum covalency of the first member of each group cannot exceed four.

B) The first member of the p-block element displays greater ability to form pπ-dπ multiple bonds to itself and to the other second period elements, compared to subsequent members of the group.

C) Anomalous behavior is due to small size, large charge/radius ratio, and high electronegativity of the elements.

D) All second-period elements exhibit a diagonal relationship.

Answer 1

In the periodic table, all the elements have their own special properties. However, certain elements display different properties than the other elements in the group. For the elements in the second period, the atomic number goes on increasing, the atomic radius of the elements decreases. Hence electronegativity increases. These elements can form a maximum of four bonds.

Complete answer:

The first element of each group that is for group 1 (lithium), group 2 (beryllium), and group 13-17 (boron to Fluorine) elements exhibit different properties than the other members of the group. This difference in the behavior of the first element of each group is due to the following reasons:

1. Size of an atom

2. Electronegativity

3. Charge to radius ratio

For the elements in the second period the atomic number increases, the atomic radius of elements goes on decreasing, the electronegativity of elements increases, and thus their ionization energy increases.

Due to higher electronegativity and small size of an atom, the lithium and beryllium (group 1 and group 2) elements are found to be least metallic in the period and they exhibit non-metal properties. The elements which are present in the second period and have extreme properties compare to the respective group. For example fluorine is a highly reactive halogen, lithium is the least reactive alkali metal compared to the other group 1 metals.

Due to the smaller size of an atom, charge is concentrated on the smaller nucleus with a high charge. Thus second-period elements have a high charge to radius ratio. The anomalous properties of the second period because of the absence of d-orbital. Thus they require higher energy to form bonds.

The second-period elements use 2s and 2p orbitals for bonding. There are a total of 4 valence electrons that take part in the bonding. Thus bonding in the second-period elements is restricted to form 4 bonds in general.

Thus anomalous behavior of any group second period element is due to small size, large charge/radius ratio, and high electronegativity of the elements, and covalence cannot exceed four.

Hence, (A) and (C) are the correct option.

Note: Note that, we say that the second-period elements form 4 bonds. However, there is an exception. N is expected to have more than the 4 bonds but it forms 3 bonds while if we compare it with its group element phosphorus it forms 5 or 6 bonds which are quite common.