CBSE Class 11 Chemistry Hydrogen Notes Set 02

Subject: Chemistry

Class: XI

Chapter: Hydrogen

Top concepts

1. Hydrogen is the lightest element known since it has an atomic mass of 1.0079

2. Hydrogen resembles Group 1 elements because it has electronic configuration (1s¹) similar to alkali metals and can loose one electron to form unipositive ions

3. Hydrogen also resembles elements of group 17 (Halogens) because hydrogen just like halogens needs just one electron to acquire the configuration of the nearest noble gas i.e. Helium

4. Hydrogen has three isotopes - Protium, deuterium and tritium

5. In elemental form Hydrogen exists as a diatomic molecule H2 and is called dihydrogen

6. Water gas is name given to the mixture of carbon monoxide and hydrogen. Water gas is also called synthesis gas or syngas

7. The production of dihydrogen can be increased by reacting carbon monoxide of syngas mixtures with steam in the presence of iron chromate as catalyst. This reaction is called as water gas shift reaction

8. The process of producing 'syngas' from coal is called 'coal gasification'

9. Physical properties of dihydrogen
· Hydrogen is a colorless, odorless and a tasteless gas
· Hydrogen is highly combustible
· Hydrogen is lighter than air
· Hydrogen is insoluble in water

10.The binary compounds of hydrogen with other elements are calledhydrides

11.Ionic hydrides or Saline hydrides are binary compounds of hydrogenwith s- block elements which are highly electropositive

12. Covalent or molecular hydrides are binary compounds of hydrogenwith elements of comparatively high electronegativity such as p-block elements

13. Covalent hydrides are classified as electron rich, electron deficient orelectron precise hydrides

• Electron rich hydrides have excess electrons than required to formnormal covalent bonds. Excess electrons are present as lone pairs .Examples of this are hydrides of group 15, 16 and 17 such as ammonia, water etc.

• Electron deficient hydrides do not have sufficient number of electronsto form normal covalent bonds. Examples of this are hydrides of group 13

• Electron precise hydrides have required number of electrons to writethe conventional Lewis structure. Elements of group 14 like carbon, silicon etc. form these types of hydrides.

14.Metallic hydrides or Interstitial hydrides are the compounds ofhydrogen with transition metals of group 3,4,5 of d-block, Cr metal of group 6, f-block element

15.Since the composition of metallic hydrides does not correspond tosimple whole number ratio they are also called non-stoichiometric hydrides

16. Due to high polarity, water dissolves most of the polar substances

17.Due to hydrogen bonding water has high boiling point and high heatof vaporization

18.Density of water is more than that of ice

19.Water has maximum density (1g/cm³) at 4 ^oC

20. Water is amphoteric in nature because it has the ability to act as anacid as well as base  

21.Autoprotolysis or self ionization of water: One water molecule acts as an acid by donating a proton to another water molecule which acts as a base. This is also called autoprotolyis of water

22.Water free from soluble salts of calcium and magnesium is called soft water

23.Water containing soluble salts of calcium and magnesium in form of hydrogen carbonate, chlorides and sulphates is called hard water 24.Temporary hardness in water is due to soluble salts of hydrogen carbonates of magnesium and calcium

25.Permanent hardness in water is due to soluble salts of chlorides and sulphates of calcium and magnesium

26. Methods to remove temporary hardness

• Boiling: During boiling soluble magnesium hydrogen carbonate is changed to magnesium hydroxide and calcium hydrogen carbonate on heating gets converted into calcium carbonate. Magnesium
hydroxide and calcium carbonate being insoluble is filtered off

27.Methods to remove permanent hardness
• Treatment with washing soda (sodium carbonate) : Washing soda reacts with hard water forming insoluble metal carbonate which can be filtered and removed

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