The P Block Elements(Group 15-18)

The p-block elements from Group 15 to Group 18 encompass a diverse array of chemical elements.

• Group 15, known as the Nitrogen Group or Pnictogens, consists of nitrogen, phosphorus, arsenic, antimony, and bismuth. These elements display various properties, ranging from the diatomic gas nitrogen to the metalloid bismuth.
• Moving to Group 16, termed the Chalcogens, we encounter oxygen, sulfur, selenium, tellurium, and polonium. These elements exhibit considerable variability in properties, from the essential diatomic gas oxygen to the toxic radioactive element polonium.
• Group 17 comprises the Halogens, including fluorine, chlorine, bromine, iodine, and astatine. These elements are highly reactive nonmetals, with fluorine being the most reactive and iodine being a lustrous solid.
• Finally, Group 18, the Noble Gases or Inert Gases, consists of helium, neon, argon, krypton, xenon, and radon. These elements are characterized by their filled valence electron shells, rendering them essentially inert and unreactive under normal conditions.

1.0p-block Elements Chart

2.0Periodic Trends in Group 15

Electronic Configuration

In Group 15, the valence shell configuration is ns²np³. This uniform arrangement leads to similar chemical behaviour among the elements. The fully-filled s-orbital and half-filled p-orbitals increase their stability compared to neighbouring elements.

Atomic and Ionic Radii

As you descend Group 15 elements, additional orbitals are added to the atoms, increasing both atomic and ionic radii. However, the increase in ionic radius from arsenic to bismuth is relatively small. This is due to the presence of filled d and f orbitals in the heavier members, which counteracts the expected increase in size.

Ionization Enthalpy

Ionization energy measures the energy needed to remove an electron from an atom's outermost orbit, indicating the nucleus's grip on the electron. As we descend a group, atomic radius increases, weakening the nucleus's hold and lowering ionization energy.

Electronegativity

Electronegativity decreases down the group as atomic size increases. This trend occurs because the distance between the nucleus and the valence shell increases as we move down the group.          

Physical Properties

• All elements in this group exhibit polyatomic characteristics. Dinitrogen is a diatomic gas, whereas the others exist as solids. 
• Metallic character increases down the group, transitioning from nonmetals like nitrogen and phosphorus to metalloids like arsenic and antimony, and finally to the metal bismuth. This trend is driven by a decrease in ionization enthalpy and an increase in atomic size.
• Boiling points generally increase from top to bottom in the group. However, melting points increase to arsenic and then decrease to bismuth. Except for nitrogen, all elements display allotropy.
  

Chemical Properties

• In this group, standard oxidation states are -3, +3, and +5. Moving down, the tendency for -3 decreases due to increased size and metallic character, with bismuth hardly forming -3 compounds. The stability of +5 decreases, as seen in BiF₅ as the sole well-characterized +5 compound. Conversely, the stability of +3 increases due to the inert pair effect.
• Nitrogen shows +1,+2, +4, and +5 with oxygen. Phosphorus displays +1 and +4 in some oxoacids.
• In acids, nitrogen's states from +1 to +4 are disproportionate, as do phosphorus's into +5 and -3 in both acid and base.

   For example, 3HNO₂ → HNO₃ + H₂O + 2NO

• Arsenic, antimony, and bismuth favor +3 due to stability. Nitrogen's maximum covalency is 4, while heavier elements utilize vacant d orbitals to expand covalency, like in PF₆.

3.0Periodic Trends in Group 16

Electronic Configuration

The elements of Group 16, namely oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po), with general electronic configurations ns²np⁴, are collectively referred to as the oxygen family or chalcogens. Oxygen and sulfur are nonmetals; selenium and tellurium are metalloids; and polonium is a metal. Polonium is radioactive and has a short half-life of 13.8 days. All these elements exhibit allotropy. Polonium is radioactive

Atomic and Ionic Radii

The group's atomic and ionic radii increase from top to bottom due to adding more electron shells.

Ionization Enthalpy

Ionization enthalpy decreases down the group as the atoms increase in size. The first ionization energy (IE1) of Group 16 elements is lower than that of Group 15 due to the extra stability conferred by half-filled p-orbitals in the latter.

Electron Gain Enthalpy

Oxygen, being more compact, exhibits lower electron gain enthalpy than sulfur. Down the group, electron gain enthalpy decreases after sulfur.

Electronegativity

Electronegativity decreases down the group, indicating an increase in metallic character from oxygen to polonium.

Melting and Boiling Point

The melting and boiling points increase with increasing atomic number down the group. The significant difference between the melting and boiling points of oxygen and sulfur can be attributed to their atomicity; oxygen is a diatomic molecule (O₂), whereas sulfur is a polyatomic molecule (S₈).

Oxidation States

Group 16 elements commonly exhibit -2, +2, +4, and +6 oxidation states. As we descend down the group, the stability of the -2 oxidation state diminishes due to the increasing atomic size and decreasing electronegativity of the elements.

Oxygen typically shows only the -2 oxidation state, except when combined with the highly electronegative fluorine, with which it can exhibit positive oxidation states. Sulfur typically exhibits the +6 oxidation state only when combined with oxygen or fluorine.

Physical Properties

• Oxygen and sulfur are nonmetals; selenium and tellurium are metalloids; polonium is a metal. Polonium is radioactive and has a short half-life of 13.8 days. All these elements exhibit allotropy.
• Melting and Boiling Points: The melting and boiling points generally rise as we progress down the group with increasing atomic numbers.

Chemical Properties

Group 16 elements exhibit various oxidation states.

• Oxygen usually shows -2 except in OF₂ (+2).
• Sulfur, selenium, and tellurium commonly display +2, +4, and +6, with +4 and +6 being more common. 
• Stability: The stability of the +6 oxidation state decreases down the group, while the stability of the +4 oxidation state increases due to the inert pair effect. Bonding in +4 and +6 states is mainly covalent. Polonium hardly shows -2.

4.0Periodic Trends in Group 17

Electronic Configuration

All these elements possess seven electrons in their outermost shell, denoted as ns²np⁵, which is one electron less than the electron configuration of the next noble gas.

Atomic and Ionic Radii

Halogens possess the smallest atomic radii in their respective periods due to the maximum effective nuclear charge.

Ionization Enthalpy

Halogens exhibit very high ionization enthalpy owing to their small size compared to other groups.

Electron Gain Enthalpy

Halogens exhibit the highest negative electron gain enthalpy since they are only one electron away from attaining a stable noble gas configuration. However, electron gain enthalpy decreases in magnitude down the group due to the increasing atomic size.

Electronegativity

Halogens are highly electronegative, with electronegativity decreasing down the group. They possess a highly effective nuclear charge.

Bond Dissociation Enthalpy

The order of bond dissociation enthalpy is Cl₂ > Br₂ > F₂ > I₂.

This order arises because as size increases, bond length increases.

Cl₂ has a higher bond dissociation enthalpy than F₂ due to significant electronic repulsions in F_2.

Colour

Halogens exhibit colouration due to the absorption of radiation in the visible region, which stimulates outer electrons to higher energy levels.

Oxidizing Power

Halogens act as oxidizing solid agents due to their strong tendency to accept electrons.

The order of oxidizing power is: F₂ > Cl₂ > Br₂ > I₂.

Chemical Properties

• Reactivity: Highly reactive, forming compounds with metals.
• Oxidizing Ability: Strong oxidizing agents form metal halides.
• Displacement Reactions: Halide ions can be displaced in the solution.
• Formation of Halides: React with metals to form halides; reactivity decreases down the group.
• Bleaching Properties: Commonly used as bleaching agents.
• Reaction with Organic Compounds: React with hydrocarbons to form halogenated organic compounds.

5.0Periodic Trends in Group 18

Electronic Configuration

Group 18 of the periodic table consists of the noble gases. The general electronic configuration of elements in Group 18 is ns²np⁶, where "n" represents the principal quantum number of the valence shell.

Ionization Enthalpy

Halogens possess exceptionally high ionization enthalpy attributed to their fully occupied orbitals. However, ionization enthalpy diminishes down the group owing to the expanding atomic size.

Atomic Radii

Atomic radii increase down the group as the number of shells increases.

Electron Gain Enthalpy

They exhibit large electron gain enthalpy due to their stable electronic configuration.

Melting and Boiling Point

The low melting and boiling points of halogens is due to weak forces between their molecules.