Plus One Chemistry Notes Chapter 9 Hydrogen is part of Plus One Chemistry Notes. Here we have given Kerala Plus One Chemistry Notes Chapter 9 Hydrogen.
|Text Book||NCERT Based|
|Category||Plus One Kerala|
Kerala Plus One Chemistry Notes Chapter 9 Hydrogen
Hydrogen has the simplest atomic structure ail the elements around us in nature. It consists of only one proton and one electron.
Position of Hydrogen in the Periodic table
Hydrogen is the first element in the periodic table. Although hydrogen resembles with both alkali metals and halogens it differs from both in certain aspects. Hence hydrogen is usually shown on the left side of the periodic table on the top of the alkali metals, but separated from them to indicate its distinctive character. Hydrogen occupies a special position in the periodic table and not associate it with any particular group.
Loss of electron from hydrogen atom re-suits a nucleus (H+) of nearly 1.5 x 103 pm size. This is extremely small as compared to normal atomic and ionic sizes of 50 to 200 pm. H+ does not exist freely and always associated with other atoms or molecules.
Resemblance with Alkali Metals (Group 1)
- Electronic configuration (ns1). Hydrogen atom has one electron in the outermost shell like the alkali metals.
- Electropositive character. Both hydrogen and alkali metals have a tendency to lose one electron to form unipositive ion.
- Oxidation state. Both hydrogen and alkali metals exhibit an oxidation state of +1 in their compounds.
- Liberated at cathode. Both hydrogen and alkali metals are liberated at the cathode.
- Affinity for non-metals. Both hydrogen and alkali metals combine with halogens to form halides, with oxygen to give oxides and with
sulphur to give sulphides.
Resemblance with Halogens
- Non metallic nature and atomicity. Hydrogen is a gas like fluorine and chlorine. H2 molecule is diatomic like F2, Cl2, Br2 and l2.
- Electronic configuration. Like halogens, hydrogen requires one electron to achieve a noble gas configuration.
- Oxidation state of hydrides and halides. Both hydrogen and halogens exhibit oxidation state of -1 in its compounds.
- Liberation at the anode.
- Substitution of hydrogen by halogens Or combination with non metals
Hydrides : CH4, SiH4, Halides: CCI4, SiCI4
- Ionisation enthalpy. The ionisation enthalpy of hydrogen is closer to halogens and much different from alkali metals. ΔiH of F is 1680 and that of H is 1312 kJ/mol.
Differences from Alkali Metals
- Alkali metals are typical metals while hydro-gen is a non metal.
- Hydrogen is diatomic (H2) while alkali metals are monoatomic in nature (Li, Na).
- Ionisation energy of hydrogen is very high as compared to alkali metals.
- Compounds of hydrogen are mainly covalent (HCI, H2O) while those of alkali metals are ionic (NaCI) in nature.
Differences from Halogens
- Hydrogen form hydrides (H–) while halogens forms halides (x).
- The oxides of hydrogen is neutral (H2O) while oxides of halogens are acidic (Cl2O7 ).
- Hydrogen is univalent while halogens exhibit variable valency.
- Hydrogen has poor affinity for metals while halogens have strong affinity for metals.
Occurence of Hydrogen
Dihydrogen is the most abundant element in the universe (70%). In the free state it is present in the atmosphere of the sun and many stars. It is much less abundant (0.15% by mass) in the earth atmosphere. In the combined state it constitutes 15.4% of the earth crust and the oceans. Hydrogen is present in water, carbohydrates, proteins, hydrides, hydrocarbons etc. and accurs in plant and animal tissues.
Isotopes of Hydrogen
There are three isotopes of hydrogen with j mass numbers 1, 2 and 3. They are called protium, deuterium and tritium respectively. Their natural abundances are in the ratio 1 : 1.56 x 10–2: 1 x 10-17 respectively.
- Protium (ordinary hydrogen) (). It is the most abundant isotope of hydrogen. Its nucleus contains one proton and no neutron.
- Deuterium (heavy hydrogen, ().or D
Heavy hydrogen is prepared from heavy water ; (D2O) which is obtained by electrolysis of ordinary water.
- Tritium (). It has 2 neutrons in nucleus.
Name the isotope of hydrogen which contains equal number of protons and neutrons.
No. of protons (p) = no. of electrons = atomic no. = 1
No. of neutrons (n) = mass no.atomic no. =2-1=1 p= 1, n= 1
Write the name of that isotope of hydro-gen which has no neutron.
Protium or ordinary hydrogen Dihydrogen is hot particularly reactive because of its high bona dissociation enthalpy. However, hydrogen forms compounds with almost all elements at high temperature or in presence of catalysts.
Uses of Hydrogen
- Hydrogen is used in the manufacture of ammonia by Haber process, water gas, fertilisers etc.
- It is used in the hydrogenation of vegetable oils an has a reducing agent.
- It is used in the production of methanol and synthetic petrol.
- It is used in oxyhydrogen torch used for welding.
Binary compounds of hydrogen with other elements are called hydrides. It can be expressed as EHx(MgH2) or EmHn (B2H6).
Ionic or Saline Hydrides
There are stoichiometric compounds of H2 formed with most of the s-block elements which are highly electropositive in character. The ionic hydrides are crystalline, non-volatile and non-conducting in solid state. In molten state, ionic hydrides conduct electricity. Salts like hydrides are strong bases such as
LiH, BeH2, MgH2.
Covalent or Molecular Hydrides
Covalent hydrides are formed by most of the p-block elements. It have very low conductivity and are acidic in nature. Covalent hydrides are soft and have very low melting and boiling points,
eg., CH4, NH3
Molecular hydrides are further classified according to the relative numbers of electrons and bonds in their lewis structure.
- Electron-deficient hydrides.
These hydrides are deficient in electrons to write their conventional lewis structure,
eg: group 13 elements (B2H6).
- Electron-precise hydrides.
These hydrides have the required no: of electrons to write their conventional lewis structure,
eg., group 14 elements (CH4).
- Electron-rich hydrides.
These hydrides have excess which are present as lone pairs, eg, group 15-17 elements
(NH3 has 1 lone pair, H2O has 2 lone pairs).
Metallic or Interstitial Hydrides (Non-stoichiometric)
These hydrides are formed by many d-block and f-block elements. Metallic hydrides are hard, possess frletalic lusture, conduct electricity and show magnetic properties,
eg., LaH287, Y6H255. These hydrides are non-stoichiometric being deficient in hydrogen.
Water is the most abundant compound in the biosphere of the total estimated global water supply of nearly 1.4 x 109 Km3, the oceans and inland saline water bodies hold 97.3% and fresh water amounts to only 2.7%.
Structure of water
In the gas phase water is a bent molecule with a bond angle of 104.5° and O-H bond length at 95.7 pm.
Structure of ice
Ice has a highly ordered 3 dimensional hydrogen bonded structure. In the normal hexagonal ice, each oxygen atom is tetrahedrally surrounded by other oxygen atoms. Density of ice is less than that of water.
Chemical Properties of Water
Amphoteric Nature: It has the ability to act as an acid as well as a base i.e., it behaves as an amphoteric substance. In the bronsted sense it act an an acid with NH2 and a base with H2S.
Redox Reaction involving Water.
Water can be easily reduced to dihydrogen by highly electropositive metals.,
Due to high dielectric constant, water has a very strong hydrating tendency.
Water has the ability to form compounds with some metal salts. These compounds are called hydrates, Interstitial water: BaCI2, 2H2O
Co-ordinated water: [Cr(H2O)6]3+3Cl–
Hydrogen bonded water: [Cu(H2O)4]SO42-, H2O in CuSO4, 5H2O
Hard and Soft water
Water which form lather with soap solution readily is called soft water,
eg., rain water, distilled water. Water which does not produce a ready and permanent lather with soap solution is called hard water,
eg., sea water, river water.
Temporary and Permanent Hardness
Temporary hardness is due to the presence of dissolved bicarbonates of Ca and Mg in water.
Permanent hardness is due to the presence of dissolved chlorides and sulphates at calcium and magnesim.
Chemical Properties of Water (H2O)
- Oxidising properties of H2O.
- Oxidises lead sulphide to lead sulphate,
PbS + 4H2O2 → 4H2O + PbSO4
- Reducing properties of H2O.
- Reduces chlorine to hydrochloric acid.
Cl2 + H2O2 → 2HCI + O2
- H2O2 is stored in a wax lined glass or plastic vessel in dark in order to prevent oxidation.
Uses of H2O2
- Mild bleaching agent, oxidising agent, disifectant and antiseptic.
- In the manufacture of some chemicals like sodium perborate, epoxides etc.
Heavy Water D2O
Heavy water is deuterium oxide D2O. It is extensively used as a moderator in nuclear reactors and in exchange reactions for the study of reaction mechanisms.
We hope the Plus One Chemistry Notes Chapter 9 Hydrogen help you. If you have any query regarding Kerala Plus One Chemistry Notes Chapter 9 Hydrogen, drop a comment below and we will get back to you at the earliest.