Topic: B.Tech, M.Tech Topic: B.Tech, M.Tech Amlan Nag Univ.Of Alberta(Canada) Amlan Nag Univ.Of Alberta(Canada) The p Block Elements – Introduction The right side of the periodic table having group number 13, 14, 15, 16, 17 and 18 are known as p – block elements. These elements have 3, 4, 5, 6, 7 and 8 electrons in their outer most shell, respectively. The last electron of these groups’ elements occupies the position in p – sub shell that is why are added as p – block elements. Their general configuration is ns2np1-6. Some important properties of p-block ! (1) Electron affinity Illustration 1. Electron affinity increase from left to right along the period amongst Which of the following arrangements represent the correct order of the p – block elements and it decreases from top to bottom. But electron affinity of the given atomic species? group 15 is having exceptionally low values of electron affinity and is (A) F < Cl < O < S (B) S < O < Cl < F due to extra stability because of the presence of exactly half filled (C) O < S < F < Cl (D) Cl < F < S < O orbital in their valence shell. Similarly, elements of group 18 (noble Solution: © gases) have zero affinities due to presence of complete octet which provides then stability. The elements of groups 15 are nitrogen (N), phosphorous (P), (2) Metallic Character arsenic (As), antimony (Sb) and bismuth (Bi). The first two elements The metallic character is governed by N and P are non – metal. The next two, arsenic and antimony are (i) Size of atoms and metalloids whereas the last element, bismuth is a metal. The general (ii) Ionization energy. electronic configuration of this group is ns2np3. The elements having bigger size and low ionization energy has a General Introduction to the nitrogen family members greater metallic character. After combining both above mentioned Nitrogen (N) factors we observe that the elements with above two properties are Nitrogen gets its name from a mineral known as “niter” (potassium located in left corner of p – block and strong non – metallic elements nitrate), from which it can be prepared. It was discovered by a are located at right corner and a diagonal strip of elements Scottish physician Daniel Rutherford in 1770. separates thus two, having in between properties are called as Nitrogen is a fairly common element in the earth’s crust. It is most metalloids. important constituent of atmosphere, making up to 78.08 %. The (3) Oxidation state greatest use of nitrogen is in ammonia which is used for fertilizer The p – block elements show variety of oxidation states both positive production and to produce nitric acid. Nitrogen gas is used where and negative. Some of the p – block elements show different inert atmosphere is needed, such as in an ordinary light bulb. oxidation state due to inert – pair effect, where their lower oxidation Nitrogen is also used in protecting historic documents. Nitrogen is state is more predominant. also used in storage of food stuff and in explosives. Some important characteristics of p – block in tabular form Nitrogen is absolutely essential to all living organisms. It is important part of all protein molecules which, among other functions, are the building materials in all kinds of cells. Nitrogen oxides (from combustion) are one of the cause of toxic rain. Ambikapatty, Silchar-4 9476699055 Page !1 Ambikapatty, Silchar-4 9476699055 Page !2 Topic: B.Tech, M.Tech Topic: B.Tech, M.Tech Amlan Nag Univ.Of Alberta(Canada) Amlan Nag Univ.Of Alberta(Canada) Phosphorous (P) growth. Most infamous use of arsenic is a poison. Arsenic also used Phosphorous got its name because it glows in the dark. in semi conductor devices along with phosphorus. “Phosphorous” is from the greek word phos (light) and phoros Antimony (Sb) (bearer). It was first isolated in 1699 by German physician Henning The name antimony is derived from the Latin words “anti + monos” Brand. He discovered it from urine. which means “not alone”. The symbol for antimony comes from its It is a non – metals. As a gas it is colourless, but it occurs in 3 original Latin name stibium. It was studied by Nicholos Lemery in allotropic form in solid state. There are white (or yellow) 17th century. phosphorous, red phosphorous and black phosphorous. The most The standard state of antimony is solid at 298 K. It is very brittle common and reactive of which is white (or yellow) phosphorous and flakes easily. Antimony has a bluish – white metallic sheen. It is which looks like a waxy. Transparent solid with a garlic like odour. a poor conductor of heat and electricity. It is known to be severely Red phosphorous is much less reactive. It is red powder and does toxic. It causes damage to the liver and is used in some cases to not dissolve in most liquids. induce vomiting and sweating. Black phosphorous is produced by heating white phosphorous in the It is added to iron and iron alloys to increase its hardness, stiffness presence of a mercury catalyst and a seed crystal of black and reduce corrosion. Antimony sulphides are used in the phosphorous. It is least reactive, does not ignite easily. vulcanization of rubber as well as in pigments. Commercially, phosphorous compounds are used in the manufacture Bismuth (Bi) of phosphorus acid (H3PO4) which is found in soft drinks, used in It’s name came from the German word Wissmuth which means fertilizers. Also phosphorous is used in fireworks, phosphorescent “white mass”. Its symbol is Bi from Bismuth. It was distinguished compounds. Phosphorous is used in forming china clay. Also used in from tin and lead by Claude Geoffroy in 1753. glass making. Bismuth is the heaviest non – radioactive naturally occurring Arsenic (As) element. It is a hard, brittle metal with an unusually low melting It was first recognized as an element by alchemists. Although it is point (271°C). Bismuth is a white – silvery crystalline, brittle metal not certain where and when arsenic was actually discovered, credit with a pinkish tinge. It is rare metal usually arrociated with copper, for the discovery usually goes to alchemist Albert the great in 1250 lead, tin, silver and gold ores. AD. It unusual property to expand upon solidification makes it useful in Arsenic is occasionally found as a free element, but it is usually type – metal alloys and for coating. Bismuth is used in wide variety found in a number of minerals. Elemental arsenic occurs in two solid of pigments ranging form cosmetics to the coloration of glass. modifications: Yellow and grey or metallic. It is a steel gray, very Illustration 1. brittle, crystalline metalloid. Arsenic does not melt when heated but Why the first ionization energy of group 15 elements much higher changes directly in to a vapour (sublimation). Arsenic is stable in dry than those of corresponding group 14 elements? air, but the surface oxidizes slowly in moist air to give a bronze Solution: This is due to increase in nuclear charge and extra stable tarnish and finally a black covering to the element. When heated in configuration of the elements of this group. The extra stability of air, arsenic combines with oxygen to form arseneous oxide (As2O3). configuration is attributed to the exactly half filled p – orbitals in A blue flame is produced and the compounds give off distinctive their valence shells. garlic – like odour. Illustration 2. It is necessary ultra trace element for humans, red algae, chickens, Why the tendency of catenation is less in nitrogen as compared to rats, goats and pigs. A deficiency of arsenic results in inhibited carbon? Ambikapatty, Silchar-4 9476699055 Page !3 Ambikapatty, Silchar-4 9476699055 Page !4 Topic: B.Tech, M.Tech Topic: B.Tech, M.Tech Amlan Nag Univ.Of Alberta(Canada) Amlan Nag Univ.Of Alberta(Canada) Solution: The lesser tendency of nitrogen to catenate as compared Nitrogen has one special feature that it can form pπ – pπ multiple with carbon can be understood in terms of their bond energies, as bonds with itself, carbon and oxygen due to its small size. In listed below. phosphorus rather pπ – pπ, dπ – pπ is found as in POX3 1. Hydrides All elements of this group form gaseous hydrides of the type MH3. ! The stability however decreases down the group for these hydrides. As there is a big drop in the bond energy from carbon to nitrogen, NH3 PH3 AsH3 SbH3 BiH3 evidently the tendency of catenation decreases enormously. Ammonia Phosphine Arsine Stibine Bismuthine Illustration 3. All the hydrides are strong reducing agents and reacts with metal Which allotrope of phosphorous is used on top head of match stick? ions to give phosphides, arsenides or antimonides. Phosphine and Solution:Red Phosphorous. other hydrides of heavier members of this groups are highly GENERAL TRENDS IN PHYSICAL PROPERTIES poisonous. ! ! Structure of Hydrides Illustration 1. Name three allotropes of phosphorous? Which of the three is most reactive? Solution: White or yellow, red and black. White phosphorus is most reactive. CHEMICAL PROPERTIES OF GROUP 15 As we move down the group there is a decrease in covalent character. N > P > As > Sb > Bi Nitrogen is chemically less reactive, due to high stability of its molecule, N2 in which two nitrogen atoms are combined through triple covalent bonds (N " N) from which one is sigma (#) and two ! are pie ($) bonds, thus posses high bond strength (941.4 KJ mol-1). Ambikapatty, Silchar-4 9476699055 Page !5 Ambikapatty, Silchar-4 9476699055 Page !6 Topic: B.Tech, M.Tech Topic: B.Tech, M.Tech Amlan Nag Univ.Of Alberta(Canada) Amlan Nag Univ.Of Alberta(Canada) ! Nitrogen forms three different hydrides with hydrogen (i) NH3 (ii) Hydrazine, NH2NH2 (iii) Hydrazoic acid, N3H Ammonia (NH3) is one of the very important hydride found in traces ! in atmosphere.