Definitions [4]
Define catalytic hydrogenation.
catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of catalyst like Ni, Pt or Pd to convert them into solid vanaspati ghee.
Definition: Hydrogen
Hydrogen is the first and lightest element in the periodic table. It is the most abundant element in the universe, constituting about 70% of the total mass of the universe and 91% of total atoms.
Definition: Alkali Metals
The Group 1 elements (Li, Na, K, Rb, Cs, Fr) are collectively called alkali metals. All elements except Hydrogen in this group are called alkali metals.
Definition: Alkaline Earth Metals
The Group 2 elements (Be, Mg, Ca, Sr, Ba, Ra) are called alkaline earth metals. They are less reactive than alkali metals. Radium (Ra) is the first radioactive element in this group, discovered by Madame Curie.
Key Points
Key Points: Hydrogen
- Electronic configuration: 1s¹ — it exists as a diatomic molecule H₂ called dihydrogen.
- Hydrogen does not belong to any group definitively; it resembles both alkali metals (loses 1 electron) and halogens (gains 1 electron).
- Alkali metals have oxidation number +1, and alkaline earth metals have oxidation number +2 in all their compounds.
Isotopes of Hydrogen:
| Isotope | Symbol | Atomic Number (Z) | Atomic Mass (A) | Natural Abundance |
|---|---|---|---|---|
| Protium |
\[_1^1HorH\] |
1 | 1 | 99.98% (naturally occurring) |
| Deuterium | \[_1^2HorD\] | 1 | 2 | 0.02% (naturally occurring) |
| Tritium | \[_1^3HorT\] | 1 | 3 | Trace (radioisotope) |
Uses of Hydrogen:
- Hydrogenation of oils to convert them into solid fats (Vanaspati ghee)
- Liquid dihydrogen is used as a rocket fuel
- Production of ammonia (Haber process)
- In production of methanol (from CO)
Key Points: Alkali Metals
Electronic Configurations:
| Period | Element | Symbol | Atomic No. | Electronic Configuration |
|---|---|---|---|---|
| 2 | Lithium | Li | 3 | [He] 2s¹ |
| 3 | Sodium | Na | 11 | [Ne] 3s¹ |
| 4 | Potassium | K | 19 | [Ar] 4s¹ |
| 5 | Rubidium | Rb | 37 | [Kr] 5s¹ |
| 6 | Caesium | Cs | 55 | [Xe] 6s¹ |
| 7 | Francium | Fr | 87 | [Rn] 7s¹ |
Periodic Trends in Group 1
| Property | Trend Down the Group |
|---|---|
| Atomic radius | Increases |
| Ionic radius | Increases |
| Density | Irregular trend |
| Ionisation enthalpy | Decreases (lower IE → more reactive) |
| Melting point | Decreases |
Biological Importance
- Na⁺ ions participate in the transmission of nerve signals
- High concentration of Na⁺ and low concentration of K⁺ is found in blood plasma
- High concentration of K⁺ and low concentration of Na⁺ is found inside human cells
- K⁺ ions are essential for nerve impulse transmission and maintaining osmotic balance
Uses of Alkali Metals
- Lithium is used in lithium-ion batteries
- Potassium is used in manufacturing potassium superoxide (KO₂) for oxygen generation in submarines, mountaineering, and space equipment
- Potassium chloride is used as a fertilizer
- Be is used as a moderator in nuclear reactors
Key Points: Alkaline Earth Metals
Electronic Configurations:
| Period | Element | Symbol | Atomic No. | Electronic Configuration |
|---|---|---|---|---|
| 2 | Beryllium | Be | 4 | [He] 2s² |
| 3 | Magnesium | Mg | 12 | [Ne] 3s² |
| 4 | Calcium | Ca | 20 | [Ar] 4s² |
| 5 | Strontium | Sr | 38 | [Kr] 5s² |
| 6 | Barium | Ba | 56 | [Xe] 6s² |
| 7 | Radium | Ra | 88 | [Rn] 7s² |
Periodic Trends in Group 2:
| Property | Trend Down the Group |
|---|---|
| Atomic radius | Increases |
| Ionic radius | Increases |
| Density | Irregular trend |
| Ionisation enthalpy (1st and 2nd) | Decreases up to Ba |
| Melting point | Irregular trend |
Importance of Alkaline Earth Metals
- Mg²⁺ ions are a constituent of chlorophyll — the green pigment in plants responsible for photosynthesis
- Ca²⁺ ions play a vital role in blood clotting (coagulation cascade)
- Ca²⁺ is essential for the formation and strength of bones and teeth (as calcium phosphate)
- Mg²⁺ is required for the activity of many enzymes in the body
- Ca²⁺ ions are involved in muscle contraction and nerve signal transmission
- Sr and Ba compounds are generally toxic to biological systems
Key Points: Some Important Compounds of Elements of S-block
| Compound | Preparation (Easy) | Properties (Easy) | Uses |
|---|---|---|---|
| Sodium carbonate (Na₂CO₃·10H₂O) (Washing soda) | Prepared by Solvay process: NH₃ + CO₂ + H₂O → NaHCO₃ → Na₂CO₃ | White crystalline solid; loses water on heating (efflorescent) | Used in making soap, water softening, cleaning |
| Sodium hydroxide (NaOH) | Prepared by electrolysis of NaCl solution (Castner-Kellner process) | White solid; highly soluble; strongly basic; absorbs moisture (deliquescent) | Used in petroleum refining and purification of bauxite |
| Calcium carbonate (CaCO₃) | Formed when CO₂ is passed through Ca(OH)₂ solution | Soft white solid; insoluble in water | Used in building material; making quicklime (CaO) |
| Hydrogen peroxide (H₂O₂) | Prepared from BaO₂ + H₂SO₄ → H₂O₂ | Acts as oxidizing and reducing agent; miscible with water | Used as antiseptic, mouthwash, bleaching agent |
| Lithium aluminium hydride (LiAlH₄) | Prepared by reaction: LiH + AlCl₃ → LiAlH₄ | Colourless solid; reacts violently with water | Used as strong reducing agent; preparation of PH₃ |
