GROUP VA ELEMENTS

4.1 INTRODUCTION

The elements of group VA of the periodic table comprise nitrogen, phosphorus, arsenic, Antimony and bismuth.

0.1.1 General Characteristics

 Nitrogen and phosphorus of group VA show the typical properties of non-metals. For Example, they are poor conductors of heat and electricity and give acidic oxides. Their Compounds are predominantly covalent. Arsenic and antimony are metalloids. However bismuth At the bottom of the group shows definite metallic properties. 

The metallic character increases Going down the group. Nitrogen has the greatest tendency to attract the electrons, antimony and Bismuth have the least. The trend down the group also shifts from covalent bonding to ionic Bonding.

 Phosphorus, arsenic and antimony have allotropes. Allotropes of phosphorus, i.e., red And white phosphorus are more important.

Phosphorus and other members of the group can make use of d orbitals in their bonding. This is because the energy of these orbitals is not much greater than those of the other valence Shell orbitals. For example, phosphorus can make use of its 3s, 3p and the empty 3d orbitals During bonding with other elements. 

In phosphorus one of the 3s electrons can be promoted to a vacant 3d orbital giving 5 Unpaired electrons in the valence shell. Phosphorus can thus make three or five covalent bonds. Indeed three and five are the common valencies of the group VA elements.

4.2 NITROGEN AND ITS COMPOUNDS

4.2.1 Occurrence

Nitrogen is present in free state in air as a major constituent (78% by volume). It is an Inactive gas in comparison with oxygen which is the next major constituent of air. Inorganic Compounds of nitrogen are not commonly found as minerals. In combined state nitrogen is found in all living matter including, animals and plants in The form of proteins, urea and amino acids.

4.2.2 Oxides of Nitrogen

Nitrogen forms several oxides with oxygen. Common oxides of nitrogen are N₂O, NO And NO₂. It also forms N₂O, and N₂O,.

4.3 PHOSPHORUS AND ITS COMPOUNDS

4.3.1 Occurrence

Phosphorus is the second member of group VA. Its name comes from Greek word Meaning “Light bearing”. Unlike, nitrogen it does not occur in free state in nature. Most of the Phosphorus is found in deposits of phosphate rock, i.e., impure Ca,(PO4), and apatite Ca,F(PO), As a constituent of plant and animal tissues, it is essential for their normal growth. It Occurs especially in seeds, the yolk of eggs, the nerves, brain and bone marrows, usually in the Form of lecithins. In the form of calcium phosphate, it is an essential constituent of bones. Bone Ash (80% calcium phosphate) is an important source of phosphorus.

4.3.2 Allotropes of Phosphorus

Phosphorus can exist in at least six different solid allotropic forms, of which we will Mention only three.White phosphorus is a very reactive, poisonous, volatile, Waxy, yellowish white substance, which is soluble in benzene And carbon disulphide. It exists in the form of tetraatomic Molecules (P.) which have a tetrahedral structure,it Boils at 280°C to P, vapours which dissociate above 700°C to Form P, molecules. Red phosphorus is much less reactive and less poisonous than white Phosphorus. It is prepared by heating white phosphorus in the presence of a little iodine or Sulphur as a catalyst upto 250°C in vacuum. The tetraatomic molecules of red phosphorus Combine to form macromolecules,

GROUP VIA ELEMENTS

4.4 Group VIA Elements

The group VIA of the periodic table consists of oxygen, sulphur, selenium, tellurium and Polonium. These elements are called chalcogens from the Greek for “copper giver”, because they Are often found in copper ores. The electronic configuration and physical properties of group VIA Elements.

4.4.1 General Characteristics

All the elements of group VIA are non-metals except Po which is a radioactive metal. Atomic radii, density, melting and boiling points generally increase with increase in atomic Number down the group. Ionization energies of the group members are very high which shows Their reluctance to lose electrons. Oxygen is the most electronegative element after fluorine. All

These elements show the property of allotropy. Oxygen has two allotropic forms (0, and 0.). Sulphur has 3(a, B. Y), Se has two (red and grey), Te has two (metallic and non-metallic). They also show the property of catenation. This property decreases down the group. All The elements are polymeric in nature (they form poly-atomic molecules). They attain the Electronic configuration of the nearest noble gas by gaining 2 electrons forming O¹, S², Se, etc.

• Except oxygen the other members of the group show a covalency of +2, +4, and +6, for example, SCI, SCI, SCI. +2 oxidation state is shown due to 2 unpaired electrons in the p-orbitals. +4 Oxidation state is shown when I electron from p-orbilal is promoted to the next vacant d-orbital, While + 6 oxidation state is shown when another electron from s-orbital is also promoted to the Next vacant d-orbital.

4.4.2 Occurrence

Oxygen is the most widely distributed and common of all the elements, comprising About 50% of the earth’s crust. About one-fourth of the atmospheric air by weight consists of free Oxygen and water contains nearly 89% of combined oxygen.

The calcium carbonate which occurs as chalk, limestone, marble etc, contains 48% Oxygen. Silica which is found in flint, quartz, etc, contains more than 53% oxygen by weight. Sulphur is also widely distributed in nature both as free and in combined forms. Many Important metallic ores are sulphides, e.g, galena (PbS), Zinc blende (ZnS), cinnabar (HgS), Stibnite (Sb,S,), copper pyrite (Cu,S.Fe,S,), iron pyrite (FeS₂), etc. Some important sulphates are Also found in nature, e.g. gypsum (CaSO), heavy spar (BaSO,), etc.

Sulphur also occurs in organic compounds present in animals and vegetables. Onions, Garlic, mustard, hair, many oils, eggs and proteins consist of compounds containing sulphur in Them. It also occurs as a constituent of coal and petroleum. 

This is because the energy of these orbitals is not much greater than those of the other valence Shell orbitals. For example, phosphorus can make use of its 3s, 3p and the empty 3d orbitals During bonding with other elements.