General Characteristics of p-Block Elements

The p-block of the periodic table consists of the elements of groups 13, 14, 15, 16, 17 and 18. These elements are characterised by the filling up of electrons in the outermost p-orbitals of their atoms.

As we move from top to bottom through a vertical column (group) some similarities are observed in the properties. However, this vertical similarity is less marked in the p-block than that observed in the s-block, especially in groups 13 and 15; vertical similarity is increasingly shown by the later groups. As far as the horizontal trend is concerned, the properties vary in a regular fashion as we move from left to right across a row (period).

Electronic Configuration

Among the elements of p-block, the p-orbitals are successively filled in a systematic manner in each row. Corresponding to the filling up of 2p, 3p, 4p, 5p and 6p orbitals five rows of p-block elements are there. The outer electronic configuration of the atoms of these elements is ns²np^1–6.

Atomic Size

Period

The atomic radius of the of p-block elements generally decreases on moving across a period from left to right in the periodic table. It is because the addition of electrons takes place in the same valence shell and are subjected to an increased pull of the nuclear charge at each step.

Group

On moving down a group, the atomic radius of the elements increases as the atomic number increases. This is due to the increase in the number of shells as we move from one element to the next down the group.

Ionization Enthalpy

It is the amount of energy required to remove the most loosely bound electron from the outermost shell of a neutral gaseous atom.

Period

The first ionization enthalpy of the p-block elements generally increases on moving from left to right along a period. It is because as we move from left to right along a period, the atomic size decreases. In a small atom, the electrons are held tightly. The larger the atom, the less strongly the electrons are held by the nucleus. The ionization enthalpy, therefore, increases with decrease in atomic size.

However, there are certain exceptions. The first ionization enthalpy of a group 16 element is lower than that of a group 15 element. It is because in case of a group 15 element, the electron is to be removed from the half-filled p-orbitals.

Group

The first ionization enthalpy decreases in a regular way on descending a group. It is because on descending a group, the atomic size increases. As a result the electrons are less tightly held by the nucleus and therefore, first ionization enthalpy decreases.

Electron Gain Enthalpy

When an electron is added to a neutral gaseous atom, heat energy is either released or absorbed. The amount of heat energy released or absorbed when an extra electron is added to a neutral gaseous atom is termed as electron gain enthalpy.

Period

Electron affinity generally becomes more negative on moving from left to right along a period. It is because on moving across a period, the atomic size decreases. As a result the force of attraction exerted by the nucleus on the electron increases. Consequently the atom has a greater tendency to gain an electron. Hence, electron gain enthalpy becomes more negative.

Group

On moving down a group, the electron gain enthalpy becomes less negative. This is due to the increase in atomic size and thus, less attraction for the electrons; the atom will have less tendency to gain an electron. Hence, electron gain enthalpy becomes less negative. 

But in the halogen group, the electron gain enthalpy of chlorine is more negative than that of fluorine. It is because the size of the F atom is very small which makes the addition of electron less favourable due to inter electronic repulsion. Similar situation exists for the first element of each group.

Electronegativity

Electronegativity is defined as a measure of the ability of an atom to attract the shared electron pair in a covalent bond to itself.

Electronegativity increases along the period and decreases down the group.

Fluorine is the most electronegative of all the elements. The second most electronegative element is oxygen followed by nitrogen in the third position.

Metallic and Non-Metallic Behavior

The elements can be broadly classified into metals and non-metals. Metals are electropositive in character - they readily form positive ions by the loss of electrons, whereas non-metals are electronegative in character - they readily form negative ions by the gain of electrons.

Period

Along the period the metallic character decreases, whereas non-metallic character increases. It is because on moving across the period, the atomic size decreases due to the increased nuclear charge and hence, ionization energy increases.

Group

On moving down the group the metallic character increases, whereas non-metallic character, decreases. It is because on moving down a group, the atomic size increases. As a result the ionization energy decreases and tendency to lose electrons increases. Therefore, metallic character increases and non-metallic character decreases.