What are Group-15 elements?

 These elements are called the nitrogen family. It consists of nitrogen, phosphorus, arsenic, antimony, bismuth, and meconium. They are present on the right side of the periodic table. All the elements are arranged based on their atomic weight. The elements with similar properties reside in a column called the group.

Trends in Group 15 Elements

1) Electronic configuration

•  These group elements have a general electronic configuration which is ns2np3.
• As all have the same valence electronic configuration, they belong to the same family.
• Their s-orbital always remains occupied by electrons, but the p-orbital is half-filled. That is why they are very stable elements.

2) Atomic radii and ionic radii

Atomic radii, as well as ionic radii, increase if we go from the upper elements to the lower elements. It is because of adding an extra electronic orbital. But in the case of arsenic and bismuth, this increment is not that much because of the addition of d and f orbitals. 

3) Ionization enthalpy

• Ionization enthalpy for an atom is the amount of energy required to release an electron from its outermost orbitals.
• So, for those elements whose radii are smaller, their nuclei hold their electron tightly. Thus, they require higher energy to remove an electron. 
• In case of group 15 elements, as we move down the group, the radius increases, and thereby attraction of the nucleus also decreases. So, ionization enthalpy decreases. 

4) Electronegativity

Electronegativity is the attraction of a particle towards a pair of electrons. As we move down the group of nitrogen family, we find that Electronegativity decreases because of the increment in their atomic radius. 

5) Physical properties

• Nitrogen and phosphorus are non-metals, but Arsenic and Antimony are metalloids. Only bismuth is a metal. So, as we go down the table, the metallic characteristics increase.
• All the elements are polyatomic here.
• Atomic size increases as you go down.
• Only nitrogen does not have allotropes. Others have their allotropes.
• Nitrogen is colourless; Phosphorus is red or violet; Arsenic is dull grey colour; Antimony is silver, and bismuth is a silver-white metal.
• Phosphates are very reactive. So, they are kept underwater to prevent the flame up.
• The boiling point also increases as we move down the group.
• They have a wide range of physical properties. Nitrogen is gas but liquefies at -200oC and freezes at -210oC.
• Bismuth is solid which melts at 271oC and boils at 156oC. 

6)  Chemical properties

• The valence cell of this group elements has a configuration ns2np3.
• So, the elements can accept 3 electrons or lose 5 electrons.
• The oxidation states are +5, +3, and -3.
• Due to the decreased Electronegativity, ionization enthalpy and because of the higher atomic radius, the tendency to create -3 oxidation state decreases.
• Bismuth usually does not have a -3-oxidation state.
• Getting a +5-oxidation state also decreases with coming down the group due to the inert pair effect.

Nitrogen and phosphorus present in the living cells. They help in plant growth. But arsenic is a toxic element and causes different diseases in the human body. Antimony and bismuth mainly use to make alloys. The phosphate group presents in the DNA, RNA, and nucleic acid. Bones, teeth are also made of phosphate. Phosphoproteins present in egg yolk, milk, and also in the bone marrow. Other elements present as sulphides.