Hydrogen Is the First Element in the Periodic Table and Is

Home , Azane

• Hydrogen is the first element in the periodic table and As such � gas is not found in our atmosphere because is the lightest known element. It was prepared by Herny of its lighter nature. Sun's atmosphere contains 90% of Cavendish in 1766 by the action of acids on metals. hydrogen. Earlier it was named as inflammable air then Lavoisier Isotopes named it hydrogen (in Greek hydro means water, gen means producing) because it produces water on burning with oxygen. Occurrence of hydrogen : Hydrogen is the most abundant element in the universe. It occurs in nature in @)@)iHProtium i H Deuterium �HTritium both free state as well as combined state. (Hydrogen) (Heavy hydrogen) (Radioactive hydrogen) 1 Molecular fonns : H2 (dihydrogen) 2 Free state � In air, volcanic gases, natural gases H2 or D2 (dideuterium) Combined state � In water, mineraloils , hydrocarbons, 3H2 or T2 (ditritium) fats, proteins, alkalies, acids, etc. alongwith HD, HT, DT, etc.

Protium 1 0 99.986 Stable 1/2 1.007825

Deuterium f H (D) 2 0.014 Stable 1 2.014102

Tritium iH (T) 3 1 2 7 X lQ-16 Radioactive 1/2 3.106049

• Allotropes : Ortho hydrogen and para hydrogen Preparation

1. With metals 1. From acids

,\If+ HzO -Motl From 2. With ionic hydrides water (Pam hydrogen) ouuuhydrogen) MH + H20 -..\10H At room(Ortho tem perature, ordinary hydrogen contains 75% 3. With methane y g g CH + H20 ortho-h dro en and 25% para hydro en. As the 4 -co, temperature decreases, the percentage of ortho 4. Electrolysis of water hydrogen in the mixture decreases. Pure para hydrogen f¼O�H'"+OW can be prepared by cooling nearly to absolute zero but on cathode pure ortho hydrogen cannot be prepared. Stability l> : Ortho hydrogen > Para hydrogen Properties l> Differences in physical properties of both is • Physical properties : The importantp hysical properties because of differences in internal energy of both. of dihydrogen are: Internal energy of ortho H2 > para H2• It is a colourless, tasteless and odourless gas. Ja- > It is slightly soluble in water. BeH and MgH have covalent polymeric strncture. > The hydrogen atom exists f· ion. It is lightest substance known. For example, one 2 2 as litre of hydrogen at NTP weighs only 0.0980 g. Ionic hydrides are prepared by thef direct combination > It is highly combustible and therefore should be of the metals ,vith hydrogen at high temperatures of handled carefully. 750 C. > It is non-poisonous and lighter than air (vapour ° 2Li + H2 2Lt·H- density = 1 while vapour density of air 14.5). Mol!en �° > Hydrogen is inflammable and does not= help in 800 C burning. • Characteristics of ionic hydrides • Chemical properties > Ionic hydrides are white or light grey crystalline 0 solids. They behave like salts. 2H2 0 + Heat -,, They have high melting and boiling points. 2 HX X2 > They conduct electricity in fused state. > N, Thethermal stability of the alkali metal and alkaline Heat + NH Fe/Mo earth metal hydrides follow the order: reaction Na +H2 �NaH 3 Lili > NaH > KH > RbH > CsH with Ca + H 4 CaH and CaH > SrH > BaH > Aqueous solution of ionic hydrides is basic in 2 2 2 2 2 nature. oxidesof with LiH + H 0 � LiOH + H less elecb"o unsaturated carbon hydrocarbons 2 2 electrode positive metals co, ,l HC001Yf+C + H 3MC1+ MA!H4 PbS +MOH HgO + H2 ---+Hg + H 0 CH2 =CH 2 2 200'C Ni urPt) Jle 0 + 4H ---+ 3Fe + 4H 0 CH -CH 2 SiH4 + MCI Ni or Pt ) WO3 4+ 3H 2---+W + 3H O2 CH CH + 2H 2 3 3 • Uses of Ionic hydrides and their 200°c ionic hydrides complexes are used as reducing agents. They evolve 3 2 2 CH -CH hydrogen when heated. Hence, they are used as solid Uses 3 3 fuels as they ignite spontaneously. e Used as a reducing agent in industry and laboratories. Molecular or Covalent Hydrides • Used to prepare hydrogenated vegetable solid fats. • Molecular hydrides are formed mainly by elements of • Used for welding purposes in both the oxy-hydrogen comparatively higher electronegativity as of p-block torch and the atomic-hydrogen torch, wh en elements . These hydrides, have molecular lattices held temperature of the order of 2500 °C and 4000 °C are together by weak van der Waals forces. In some cases, required respectively. hydrogen bonds are also formed. The general formula • Used as a rocket fuel in the form of liquid hydrogen. for covalent hydrides is .XH where X stands for the symbol ofa metal and 'n' is number ofvalence electrons. • Used in the manufacture of synthetic petrol. 8_n e Used in the preparation of many compounds such as • Characteristics of covalent hydrides > Molecular hydrides are soft. methane, ammonia, water gas, and fertilizers such as ,, urea, ammonium sulphate, etc. They have low _electrical conductivity. > The electronegati vity difference between • Used in metallurgy. hydrogen and the atom bonded to it, determines • Used in preparation of metal hydrides. the properties of covalent hydrides. On moving from left to right in a period, hydrides become HYDRIDES • The binary compounds formed by hydrogen with other increasingly acidic in character. For exarnple NHi elements, are called hydrides. Hydrogen combines with is a weak base, H 0 is neutral and HF is acidic. > The hydrides of Group [II ( BH and AlH ) are most of the metals and non-metals (except noble gases). 2 e.g., electron deficient compounds and exist in Hydrides are classified into three main groups, 3 3 depending upon their physical and chemical properties polymeric forms [e.g., B H and (AlH ) l- Hydrides of oup-14 CH , Sil-Li,GeH , etc.) have exact and the types of bonding: (e.g. 2 6 3 n number of electrons and hence called electron L Ionic or salt like or saline hydrides gr 4 4 2. Covalent or molecular hydrides precise hydrides. Hydrides of group-15, 16, 17 (i.e. 3. Metallic or interstitial hydrides NI--I , PH , H 0, H S, HF, HCl, etc.) have one or more lone pairs of electron around central atom 3 3 2 2 Ionic Hydrides or Saline Hydrides and hence called electron rich hydrides. • These are formed by highly electropositive metals Molecularhydrides have elements of group IA (alkali metals) and group IIA • Uses of molecular hydrides : wider applications. Some of them are mentioned here. (alkaline eaiih metals with the exception of Be and Mg). Hydrogen

Boron hydrides are used as high energy fuels and those of hydrides other members of the oxygen propellants. Phosphine is used for making Holme's group such as H2S, H2Se, H2 Te, etc., due to the signals. H2S is an important laboratory reagent. presence of intermolecular hydrogen bonding in 2 Metallic or Interstitial Hydrides H 0 molecules. • Metallic hydrides are formed by most of the d-block > Water has a high dielectric constant. So that, water elements (i.e., transition elements), on reacting with can dissolve wide variety of compounds in it. hydrogen. These are interstitial compounds and may That'swhy water is regarded as universal solvent. be regarded as solid solutions. > Water is a poor conductor of heat and electricity • Hydrides off-block elements are non-stoichiometric in However, addition of a small quantity of an acid or nature. alkali makes it conducting. • Mainly transition and inner transition elements form Water plays an important role in biosphere. metallic hydrides. • Chemical> l properties of water • Characteristics of metallic hydrides 2 with metal H CO co (M} MOH +Hz I > They conduct electricity. 2 3 non-me!allic oxides > The density of such compound is less than that Na20 of the metal itself and theirproperties are not much hydrides (metallic NaOH H Ca(OH) ( oxides) different from their respective metal i.e., they give 2 + 2 CaH2 out hydrogen easily and are strong reducing non-metals § Cl2, cold HCl + I-IClO agents. with :� alkali o Cl > Theyare black powdery, hard, have a metallic lustre CH3COONa -'), 02 COOI-I or aci � 1-. un- Hg'-h -t HCI + and magnetic properties. CH3 hydrolysis • Uses of metallichydr ides : Metallic hydrides arewidely +NaOH used in catalytic reduction and hydrogenation for water gas preparing large number of useful compounds. • Uses of water : Water is vitalto life. Humans, plants and WATER animals are made up of mostly water. AU living things • Occurrence : About 75% of the Earth's surface would die if thereis no water. Water is mainly used for consists of water. Water is present as either drinking, cleaning and irrigation crops and landscape. (a) Solid : In the form of ice, snow, etc. (b) Liquid : in the form of water in lakes, rivers and HEAVY WATER oceans, etc. • Deuteriumoxide (D20) is known as heavy water. It was (c) Water vapour : In the form of clouds or moisture discovered by Urey in 1932. It is present intrace ammmt in the air. in ordinary water (1 part in 6000 parts). • • Heavy water is prepared either by prolonged Structure : Water is3 a covalent molecule in which oxygen undergoes sp hybridisation and contains two electrolysis or by :fractional distillation of ordinary lone pairs. ,v ater. • Heavy water may contain some heavier isotopes of Due to the presence of two lone pairs of electrons on° the oxygen atom, theH- 0 -H bond angle is 104.5 . oxygen also. Molecule is angular or bent in shape. • Physical properties lone pair 1.84 D (net dipole) > Heavywater is colourless, tasteless and odourless liquid. It has all higher values for physical constant than c{i) _J_(i l> the corresponding values of ordinary water. 0 Physical properties of water and heavy water at 298 K +ciH/ '°x+ci H�H H In solid state (ice) water molecules are arranged in 1 Molecular mass (g mol- ) 18.015 20.028 l> highly ordered three dimensional open cage like structure through hydrogen bonding. Melting Point (K) 273.0 276.8 1bis arrangement leads to a packing with large Boiling-point (K) 373.0 374.4 ' 3 )> Maximum Density (g cm- ) 1.000 1.106 open spaces and results in lower density of ice 3 than that of liquid water. Density (g cm- ) (at 298 K) 0.997 1.105 • Physical properties Heat of Vaporization )> 1 Pure water is transparent, tasteless, colourless and (at 373 K)(kJ/mol- ) 40.66 4161 odourless. It readily picks up the colour and flavour Heat of Fusion (k.J moI-1) 6.01 5.68 of any substance dissolved in it_ Ionization Constant j 2 2 14 The freezing point, boiling point, heat of fusion [W][OH-J (mol L-' ) }.008 X 10- 1.95 X l(t·l ! )> and heat of vaporization of water are higher than Electrolysis D2 + 02 H H �7.Spl:!J�}o 0T o Na (at cathode) (at anode) JR.s Pm V (! o1 .9J 9 14s:?:;;-o NaOD +D2 s;:;,-o In gas phase In solid phase (110 K) NaOD Preparation DNO3 (Deutero nitric acid) - Na2S04 Na O2 + H2SO4 CaC2 2 Ca(OD)2 +DC"'CD (Deutero acetylene) cold . -BaS04.l. Ba0z-8H20 + H2SO4 ---�.... Mg(OD)2 + ND3 (Deutero ammonia) cold

- Ba3(P0412LJ, ND4Cl +HDO Ba02 + H3P04 BaS -BaCO,J Deuterolysis Ba(OD) + D2S ° 2 Ba.02 + H20 + CO2 Uses of heavy water • By autoxidation of 2-ethyfanthraquinol : Industrially • As moderator and coolant in nuclear reactor. used process for the manufacture of H2O 2 is • As a tracer compound to study various reaction autoxidation of 2-ethylanthraquinol. This method, mechanism. involves alternate oxidation and reduction steps of • For the preparation of various deuterium compound. 2-ethylanthraq11inol. • As a germicide and bactericide. HARD WATER • Water which does not produce lather with soap e.g. sea water, river water etc. Hardness of water is due to presence of bicarbonates, chlorides and sulphates of calcium and magnesium. 2-elhylanth:raqu.inol 2-ethylanthraquinone Sodium stearate (soap) changes to corresponding Ca The hydrogen peroxide formed in this reaction is or Mg salt which precipitates out as 2 2+ 2+ extracted with water, and concentrated to obtain H O2 17 35 2C H COONa + Ca /Mg � + of the required strength. (C17H35COO}iCa/Mg + 2Na Metal stearate Physical properties • Temporary hardness is due to the presence of • Its boiling point is higher than H2O due to thepresence bicarbonates of Ca and Mg. It can be removed by of stronger intermolecular hydrogen bonding than in > Boiling: water. M(HCO 3 )2 � MC 03J. + H2O + CO2 t soluble insoluble i'.Jtto:ttiff#/:y bi carbon ates carbonates (as precipitate) Colour ° Light blue C9Jou°rless b.pt. 152 C (deco° mposes) 100 c Here, M = Mg or Ca m.pt. -0.4 C O"C > Clark's process: Density 1.4 g cm- 1.0 g 3)2 2 � 3 2 3 Ca(HCO + Ca(OH) 2CaCQ 'j, + 2H O ii Magnetism Diamagnetic Parama�neticcrn-3 1 • Perm anent hardness is due to the presence of soluble chlorides and sulphates of Ca and Mg. It can be removed Chemical properties by treating it with Na2CO3 • � CaSO4 + Na2CO3 CaCO3 J.. + Na2 SO4 NaOH MgCl2 + Na2CO3 .,:::= MgCO3t + 2NaCl NaH02 +1:lzO sodium Also, removal of both types of hardness is affected hydroperoxide by ion exchangers like zeolite, pennutit and synthetic NaOH resins, etc. i-----,. Na202 +H20 OH HYDROGEN PEROXIDE Addition rHz CHz- CH CH 0H • HzO2 is known as hydrogen peroxide or oxygenated 2 2 water. glycol • Structure of hydrogen peroxide : Hydrogen peroxide bleachin agent Hp + (O] is a non-planar molecule. It has an open book like + coloured matter structure. In gaseous phase the dihedral° (interplanar) angle between two planes is 111.5 but in crystalline .J, ° colourless state it reduces to 90.2 due to hydrogen bonding. Hydrogen

54.4 g of H O will give Reducing propeities Oxidising properties 2 2 Ag PbS 22400x 54.4 p PbSO 4 mL of 02 at STP FeSO 68 + HzO H2S04 Fez(S04h Hence, 1000 rnL of H202 solution will give + l-l2S04K� K2S04 + I2 22400 x 54.4 mL of 02 at STP Na�AsO 68 Na3As04 1 mL of H2O2 solution will give sodium arsenate 22400x54.4 .92 mL ot 02 at STP K2Cr20 68xlO00 = 17 (orange) Cr05 (blue) Hence, volwne strenth of 1.6 M H20:z solution = 17.92 Concentration determination IJlttrofflMI Concentration ofH202 is expressed in terms of"volume What mass of hydrogen peroxide will be present in 2 litres of O/'. of a 5 molar solution? Calculate the mass of oxygen which 2 2 2 2 "10 volume" H 0 means that 1 mL of H 0 at NTP will be liberated by the decomposition of 200 mL of this gives 10 mL 02 gas. solution. 2 2 2 2 2H 0 --;'J> 2H 0 + 0 2 2 1 2(2 + 32) = 68 g 22400 mL at NTP Soln,: Molar mass of H O = 34 g mo1- ? x mL Mass of H2O2 present in 2 L of 5 molar H2O2 solution 22400 mL ofO2 at NTP are obtained from68 g ofH202 . 2 2 x mL of 02 at NTP obtained from = 2 5 34 = 340 g H 0 X X Mass ofH202 present in 200 mL of 5 molar H202 solution 68 -- xx gofH?Oo = - � 340 22400 =�-x200 = 34 g 2000 68x 680x 2 2 2 2 Cone. in g/L = -- x 1000 = -- g/L 2H 0 0 + H 0 224 ---0 22400 So, 68 g of H 0 on decomposition will give 32 g 02 cone. in g/L 680x 1 = x 2 2 Normality OV) = 34 g of H2O2 on deocompostion will give equiv. wt. = 224 x17 5.6

- - cone. in g/L 680x 1 x _ 32 x34 O' '1 Molarity (M) = _16 -0 C. mol. wt. = 224 x 34 = 11.2 68 ° IO®@Mlil Uses of hydrogen peroxide 2 2 Calculate the volume strength of 1.5 N H 0 solution. @ H202 is germicide and antiseptic. Volume strength s Its dilute solution is used in the bleaching of cotton, Soln,: Normality = 5_6 wool, silk, hair, ivory, paper, pulp, etc. Volume strength = 1.5 x 5.6 = 8.4 e It is used in the preparation of organic and inorganic lmtti!ti!G1tfI compounds. Na 0 sodium perborate, epoxides, peracids such as2 H2 ,2 SO5 (permonosulphuric acid, Calculate the volume strength of 1.6 M H2O2 solution. Caro's acid), H2S2O8 (perdisulplmric acid, Marshall's Soln.: As the solution is 1.6 M, its 1000 mL will have acid), etc. x = 1.6 34 = 54.4 g of H2O2 ® It is used as nropellent for rockets, torpedoes, etc., 2H202 � 2H20 + 02 and as a fuel. As a propellant is used to oxidise 68 g 1 mo! alcohol, petrol, hydrazine, etc. N2H4 + 2H202 � N2 + 4H20 22400 mL at STP • H2O2 is used as antichlor to remove Cl2 etc., present 2 2 2 Now, 68 g of H O gives 22400 mL of 0 at STP. in a solution. CONCEPT MAP

HYDROGEN

• Most abundant element 1. By actionof wat er in the uni verse . • \V ith cold wate,· rd Hydrides (211H ) Water (H O) ., 3 m ost abundant , 2 Hydrogen peroxide (H2 O2) very reacti vc metalslike A1----'), except noble element on the globe' s Na, K, Ca, etc. discovered by gases, In, Tl ( ) surface. • \Vi th·hoiling water Physical properties J.L. Thenard 1818 t e 9 h on earth. Zn, Mg Al etc. • have intermolecular , , Ionicor saline • \Vith Steam H-bonding Preparation Af has lesser Fe, Sn,Ni, etc. • high di electric • fromNa O clectronegatt vity than H con Stan L - universal 2 2 Isotopes 2. By electrolysis of water (Mark's method) Differ in number (group 1 and 2 elemenLs) solvent • from BaO2·8IIi) of neutrons H2o� ff +mr • electrolysis of 50% Chemical properties At cathode Metallic01· inte1·stitial H2S04 Protium ( ;H) 21Y -t-2e .. ----'),H = • amphoteric 2 • Ai • formhydrates ,. Most abundant 3. From alkalies d- block (group 3, 4, 5 l'l'ope1·ties ( ) • undergoes oxidation 99.984% e.g,. Zn � 2NaOH � and 10, 11, 12) • acidic • I proton, 0 nentron reduction reactions • undergoes auto Na2Zn02 +H2 - fblock elements, 4. From acids group6onlyCr oxidation a11d auto I-lea vv water (D,O) reduction Deuterium( ;H) ( or D) e.g.,Zn+H2so4 --;J> • Groups 7, 8, 9 do not • di;covered by H.C. • bleachingaction • in HDform ZnSO + H form hydride, so 4 2 Urey (l932) (0.0156%) 5. Bosch process-from known as hydride gap " addition reactions " low dielectric • 1 proton, ] neutron water gas • Non-stoichiometric catalvst constant than viater Structure H + CO + H 0 --'---,> • Shows occlusion 2 2 so ionic compounds • non-polar { steam Tritium ( H)(orT) wate� gas' are less soluble in • 2 0 - II m • unstable, radioactive CO2 +2H2 Covalent or molecular r = D�O (taces) M • u,t,d as moderator in • 1 proton. 2neutrons • p-block (MH8 _,,) nuclear reactors and (i ) • some s-bl ock: \dIIn tracer compounds elements (Be & Mg) e.g., phosphine- PH3, oxidane-H�O azane -NH3- In gas phase • Manufacture of NH (Habe1' s rocess) HCI metal 3 p , , hydrides • Hydrogenation of oils • In atomic hydrogen & oxy-hydrogen torches • Liquid hydrogen used as a rocket fu el.