Elements of p-block , General properties of group 5A elements ( group 15 )

Group 5A ( group 15 ) consists of five elements which are nitrogen , phosphorus , arsenic , antimony & bismuth , Elements of this group are not abundant in nature , except nitrogen which represents about 80 % of atmospheric air ( 4/5 ) of air volume , We can not detect both nitrogen & phosphorus by flame test , because both of them are nonmetals .

Group 5A ( group 15 )

Group 5A Elements

Group 5A Elements

The forms of these elements which are found in nature :

  • Phosphorus is the most abundant element of this group ( 5A ) in Earth’s crust , The form found in nature : Calcium phosphate Ca3(PO4)2 , Apatite CaF2.Ca3(PO4)2 ” the salt of calcium fluoride and calcium phosphate ” .
  • Arsenic : The form found in nature is Arsenic sulphide As2S3 .
  • Antimony : The form found in nature is Antimony sulphide Sb2S3 .
  • Bismuth : The form found in nature is Bismuth sulphide Bi2S3 .

General properties of group 5A elements ( group 15 )

The properties of group 5A elements graduate regularly depending on the increase in atomic number and atomic size as illustrated in the following :

  1. Graduation of the metallic and nonmetallic properties .
  2. Different number of molecules atoms of each element .
  3. Several oxidation numbers .
  4. Oxides of group 5A elements .
  5. Hydrides of group 5A elements .
The graduation of the metallic and nonmetallic property 

The metallic property increases by increasing the atomic number ( downward the group ) , The properties of this group elements tend to be those of the nonmetals , even bismuth – is a metal – but its ability to conduct electricity is weak .

Different number of molecules atoms of each element

The number of molecule atoms of each element of this group differs as the following :

  • Nitrogen : The molecule contains two atoms , Symbol of molecule is N2 .
  • Phosphorus : its vapour has molecule which contain four atoms , Symbol of molecule is P4 .
  • Antimony : its vapour has molecule which contain four atoms , Symbol of molecule is As4 .
  • Arsenic : its vapour has molecule which contain four atoms , Symbol of molecule is Sb4 .
  • Bismuth : It forms a metallic crystal lattice & its vapor consists of diatomic molecules , Symbol of molecule is Bi2 .

Although bismuth is a metal , it has different properties than that of the other metals , because of its low electric conductivity relative to the other metals and it has a diatomic structure in its vapor state , whereas the other metals have mono-atomic structure .

Several oxidation numbers

Elements of this group are characterized by having several oxidation numbers in their different compounds from ( − 3 ) to ( + 5 ) , because through covalent sharing they may gain till 3 electrons or lose till 5 electrons , The oxidation numbers of nitrogen in some of its compounds :

Oxidation numbers of nitrogen in some of its compounds

Oxidation numbers of nitrogen in some of its compounds

The oxidation numbers of nitrogen in the oxygenated compounds are positive , while that in the hydrogenated compounds are negative , Because the electronegativity of nitrogen is less than of oxygen and higher than that of hydrogen .

Several allotropic forms

Allotropy is the presence of the element in more than one form which have different physical properties and similar chemical ones , The allotropic phenomenon appears in the solid nonmetals only , Due to the presence of the solid nonmetal element in different crystalline forms , each form differs in the number of atoms and in their arrangement .

  • Phosphorus : Allotropic forms are white ( waxy ) , red , violet .
  • Arsenic : Allotropic forms are black , grey , yellow ( waxy yellow ) .
  • Antimony : Allotropic forms are yellow , black .

Allotropy exists in phosphorus , but not in nitrogen and bismuth , Because phosphorus is a solid nonmetal , while nitrogen is a gaseous nonmetal and bismuth is a metallic element , in which gases and metals do not have allotropic forms .

Oxides of group 5A elements

All elements of this group form oxides have the formula : X2O3 , X2O5 , Some of these oxides are acidic , others are amphoteric and others are basic , The basic property of these oxides increases ( the acidic property decreases ) with increasing the atomic number .

  • Element is 7N : Its oxide is N2O3 , N2O5 , Type of oxide is Acidic oxide .
  • Element is 15P : Its oxide is P2O3 , Type of oxide is Acidic oxide .
  • Element is 33As : Its oxide is As2O3 , Type of oxide is Acidic oxide .
  • Element is 51Sb : Its oxide is Sb2O3 , Type of oxide is Amphoteric oxide .
  • Element is 83Bi : Its oxide is Bi2O3 , Bi2O5 , Type of oxide is Basic oxide .
Hydrides of group 5A elements 

Most of the elements of this group react with hydrogen forming hydrides , the oxidation number of the element is −3 , as in Ammonia NH3 , Phosphine PH3  , Arsine AsH3 .

The central atom in these compounds still has a lone pair of electrons in its valence shell ( outer energy level ) , so , it can give this pair of electrons to other atoms or ions making coordinate bonds .

Based on that the basicity of the hydride depends on the ability of its central atom to lose one pair of electrons or gain a proton from another substance , ammonia is more basic than phosphine .

NH3 + H2O NH+4 + OH

PH3 + H2O PH+4 + OH

The properties of hydrides of the group 5A elements :
  1. Their thermal stability decreases , so , they decomposes even by gentle heating .
  2. The polarity of hydrogen compounds in this group decreases with increasing atomic number of the element attached to hydrogen , thus their solubility in water decreases .

The solubility degree of phosphine in water is less than that of ammonia , Because the polarity of phosphine is less than the polarity of ammonia .

The most famous elements in 5A group ( Nitrogen properties , Preparation & compounds )

Nitric acid properties , Passivity phenomenon & Economic importance of the 5A group elements

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