The p-Block Elements
Elements of group-15 consist of Nitrogen, Phosphorus, Arsenic, Antimony, and Bismuth. Nitrogen makes about 78% by volume of the atmosphere. The general outer electronic configuration of Group 15 elements is ns2np3. Properties like atomic radius, ionisation enthalpy, electronegativity, metallic character vary when we move down the group. The common oxidation states of Group15 elements are –3, +3 and +5. Group-15 elements react with hydrogen (forms hydrides), oxygen (forms oxides), halogens and metals.
Nitrogen differs from the rest of the members of this group due to its small size, high electronegativity, high ionisation enthalpy and non-availability of d-orbitals.
Elements of group-16 consist of Oxygen, Sulphur, Selenium, Tellurium and Pollonium. Oxygen is the most abundant of all the elements on earth. Dry air contains 20.946% (about 21%) oxygen by volume. It forms about 46.6% by mass of Earth’s crust. The general outer electronic configuration of Group 16 elements is ns2np4. Properties like atomic radius, ionisation enthalpy, electronegativity, metallic character show variation when we move down the group. The common oxidation states of Group16 elements are –2, +2, +4 and +6. Group-16 elements react with hydrogen, oxygen and halogens.
Oxygen differs from the rest of the members of this group due to its small size, high electronegativity, high ionisation enthalpy, non-availability of d-orbitals and tendency to form pp–pp bond with itself.
Elements of group-17 include Flourine, Chlorine, Bromine, Iodine and Astatine. The general outer electronic configuration of Group 17 elements is ns2np5. The group 17 elements have the smallest atomic radii in their respective periods. Properties like atomic radius, ionisation enthalpy, electronegativity show variation when we move down the group. The common oxidation states of group17 elements are –1and +1.
Group-17 elements react with hydrogen, oxygen and metals
Fluorine differs from the rest of the members of this group due to its small size, high electronegativity, low bond dissociation enthalpy and non-availability of d-orbitals. Halogens form a number of oxoacids.
Chlorine is a greenish yellow gas with pungent smell and suffocating odour. When chlorine is dissolved in water it forms chlorine water. Chlorine water show oxidising properties.
Hydrogen chloride is a colourless gas with pungent smell. It is highly soluble in water. Hydrogen chloride is a strong acid. It is used in the formation of aqua regia. When two different halogens react with each other, interhalogen compound is formed. Interhalogen compounds are volatile solid or liquids, covalently bonded and are diamagnetic in nature. Interhalogen compounds are more reactive than halogens (except fluorine).
Elements present in group-18 are Helium, Neon, Argon, Krypton, Xenon and Radon. The general outer electronic configuration of Group 18 elements is ns2np6. All the noble gases except radon occur in the atmosphere (about 1% by volume) of which argon is the major constituent.
Properties like atomic radius, ionisation enthalpy, electronegativity, vary as we move down the group. Noble gases are colourless, tasteless and odourless monoatomic gases. Noble gases are least reactive.
Neil Bartlett prepared a red coloured compound Xe+PtF6– by mixing PtF6 and Xe.
Xenon can form fluorides, XeF2 , XeF4, and XeF6 by the direct reaction of elements under appropriate experimental conditions. Xenon forms two oxides, XeO3 and XeO4.
Xenon forms a number of oxyfluorides such as XeOF2, XeOF4, XeO2F2, XeOF6, etc.
Helium is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations. Neon is used in glow signs. There are various uses of noble gases in different fields.
COMPOUNDS OF GROUP-15
Nitrogen is commercially prepared by liquefaction and fractional distillation of air. Dinitrogen can be prepared in laboratory by the reaction of an aqueous solution of ammonium chloride and sodium nitrite. Dinitrogen is a colourless, tasteless, odourless, non-toxic gas with very low solubility in water. Dinitrogen is neutral towards litmus. It is unreactive due to high bond enthalpy of NºN. Dinitrogen is used in the manufacture of ammonia, nitric acid, calcium cyanamide etc and other industrial purposes. Ammonia is a compound of nitrogen which can be manufactured by Haber’s process.
Ammonia is a colourless, pungent smelling gas. It is lighter than air and is highly soluble in water. It is used in the manufacture of various nitrogenous fertilisers such as urea, ammonium nitrate etc. Nitrogen forms several oxides such as Nitrous oxide (N2O), Nitric oxide (NO), Dinitrogen trioxide (N2O3), Nitrogen dioxide (NO2), Dinitrogen tetroxide (N2O4), Dinitrogen pentoxide (N2O5).
On industrial scale Nitric acid is prepared by Oswald’s process. Nitric acid is colourless fuming liquid with pungent odour in pure state. There are several uses of nitric acid.
Phosphorous is found in three allotropic forms, namely, white phosphorous, red phosphorous and black phosphorous. Phosphine is an important compound of phosphorous. Phosphine is a colourless gas, with rotten fish like smell. It is highly poisonous and is slightly soluble in water. Phosphorus forms two types of halides PX3 and PX5 Where, X = F, Cl, Br or I.
Phosphorous forms a number of oxoacids. In all oxoacids, phosphorus is tetrahedrally surrounded by other atoms. All these acids contain one P=O and at least one P–OH bond.
COMPOUNDS OF GROUP-16
Dioxygen is a colourless, tasteless, odourless gas. Dioxygen is slightly soluble in water. It has three stable isotopes, O-16, O-17, O-18. Dioxygen is neutral on litmus. O2 directly reacts with nearly all metals and non-metals except Gold, Platinum and some noble gases. O2 gas is used for artificial respiration in hospitals, by mountaineers and pilots at high altitudes etc.
Oxide is a binary compound of oxygen with another element. Oxides are classified as simple oxides and mixed oxides. Simple oxides are further classified as acidic, basic, neutral and amphoteric oxides. Triatomic molecule of oxygen is known as ozone. Ozone is formed when a slow dry stream of oxygen is passed through a silent electric discharge. Ozone is a pale blue gas with strong smell. Ozone is neutral to litmus. Ozone is used for several purposes.
Sulphur forms numerous allotropes of which the yellow rhombic (a-sulphur) and monoclinic (b-sulphur) forms are the most important. Both rhombic and monoclinic sulphur have S8 molecules.
Sulphur dioxide is a colourless gas with pungent smell. It is highly soluble in water. Sulphur dioxide is formed together with a little (6-8%) sulphur trioxide when sulphur is burnt in air or oxygen.
Sulphuric acid is one of the most important industrial chemicals because of its industrial applications. It is known as the King of chemicals. It can be prepared by contact process. Sulphuric acid is a colourless, dense, oily liquid. It dissolves in water with the evolution of large amount of heat.