(a) Elements of IA and IIA group of the periodic table are called s-block elements. Group-1 (Alkali Metals), Physical Properties, Chemical Reactivity,. Group ➣ Groups (1 & 2) belong to the s-block of the Periodic Table. ➣ Group 1 consists of: lithium, sodium, potassium, rubidium, caesium and francium and collectively. The s-Block Elements. Presented by. cavosboig.site Jit. Associate Professor. Chemistry Department. PGGCG, Sector 11,. Chandigarh.
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- Class 11 Chemistry Revision Notes for Chapter 10 - The s-Block Elements
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S Block Elements Properties in PDF Free Downloal For CBSE Notes
The elements in which the last electron enters in the outermost s-orbital are called s-block elements. They include elements of group I and II. They are collectively called alkali metals because they dissolve in water to form strong alkalies.
They are collectively called alkaline earth metals except Be because their oxides and hydroxides are found in earth crust and alkaline in nature.
The general electronic configuration of s-block elements is [noble gas] ns1 for alkali metals and [noble gas] ns2 for alkaline earth metals. Valence electronic configuration: ns1 2. Atomic and ionic radii: Increases from top to bottom. Ionization enthalpy: decrease from Li to Cs. Hydration enthalpy: decreases with increase in ionic size. Flame colouration: Alkali metals and their salts give characteristic colour to non-luminous flame. This is because the heat from the flame excites the outer most orbital electron to a higher energy level.
When this electron comes back to the ground level, they emit the radiation in the visible region. For example, Li gives crimson red, sodium gives yellow, potassium gives violet, Rubidium gives red violet and Ceasium gives blue colour to the flame. So alkali metals can be detected by flame test. Chemical Properties 1. Reaction with air: They react with air to form oxides, peroxides and super oxides.
Li forms only monoxide, sodium forms monoxide and peroxide and other alkali metals form monoxide, peroxide and super oxide. Reaction with water: The alkali metals react with water to liberate hydrogen. Reducing nature: They are strong reducing agents.
Li being the most powerful reducing agent and sodium the least. Due to the smallest atomic radius, Li has the highest hydration enthalpy.
So it has high reducing power. Solution in liquid ammonia: The alkali metals dissolve in liquid ammonia to give deep blue solutions which are good conductors.
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The solution is paramagnetic and on standing slowly liberates hydrogen resulting in the formation of amide MNH2.
Some of these are: 1. Li is much harder and has high melting point and boiling point. Li is the least reactive but the strongest reducing agent among all the alkali metals. It forms only monoxide with oxygen. LiCl is deliquescent and crystallizes as a hydrate LiCl. But the other alkali metal chlorides do not form hydrates.
Lithium bicarbonate LiHCO3 is stable only in solution. Lithium nitrate on heating gives Li2O, while other alkali metal nitrates decompose to form nitrite. Diagonal relationship between Li and Mg Li shows the following similarities in properties with Be of the second group. Both Li and Be are harder but lighter than other elements of the respective group. Both react slowly with water. Their oxides and hydroxides are much less soluble and their hydroxides decompose on heating. They do not form superoxides.
Their carbonates decompose easily on heating to form oxides and CO2.
Their chlorides are soluble in ethanol and are deliquescent. Their bicarbonates are stable only in solution. Some important compounds of Sodium 1. Sodium Carbonate [Na2CO3. Above K the monohydrate becomes completely anhydrous and changes to a white powder called soda ash. It is used in water softening, laundering and cleaning. It is used in paper, paints and textile industries.
Class 11 Chemistry Revision Notes for Chapter 10 - The s-Block Elements
It is used as a laboratory reagent. The Brine solution NaCl solution is electrolysed by using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with mercury to form sodium amalgam. Chlorine gas is evolved at the anode.
Class 11 Chemistry Revision Notes for Chapter 10 - The s-Block Elements - Free PDF Download
Uses: It is used: 1. These ions participate in the transmission of nerve signals, in regulating the flow of water across the cell membranes and in the transport of sugars and aminoacids. They activate many enzymes, participate in the oxidation of glucose to ATP and helps in the transmission of nerve signals along with sodium ions. General electronic configuration: [Noble gas] ns2 2.
Ionization enthalpy: have low ionisation enthalpy and decreases down the group. First ionization enthalpies of alkaline earth metals are higher than those of alkali metals.
Hydration enthalpy: Hydration enthalpy of alkaline earth metal ions decreases with increase in ionic size. Flame colouration Alkaline earth metals give characteristic colour to the flame. In flame the electrons are excited to higher energy levels and when they return to the ground state, energy is emitted in the form of visible light.
So calcium gives brick red, Strontium gives crimson red and Barium gives apple green colour to the flame. The electrons in Be and Mg are very strongly bound to the nucleus. So they do not get excited by the flame. Hence these elements do not give flame colouration.
Reaction with air and water Be and Mg are inert to O2 and H2O because of the formation of oxide film on their surface. Other elements form monoxide with air.
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In the vapour phase, it forms chloro-bridged dimmer. Reducing nature: Like alkali metals, group II elements are strong reducing agents.
But the reducing power is less than that of alkali metals. Solution in liquid ammonia: They dissolve in liquid ammonia to form deep blue black solution due to the formation of ammoniated electrons.
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Some of the properties are: 1. Be has high ionization enthalpy and small size.
It forms compounds which are highly covalent and get easily hydrolised. It does not show co-ordination number more than 4 as its valence shell contains only 4 orbitals. The remaining members of the group can have a co-ordination number of 6 by making use of vacant d- orbitals.
The oxide and hydroxide of Be are amphoteric in nature. BeCl2 exists as dimer even in vapour phase and is soluble in organic solvents.
Diagonal relationship between Beryllium and Aluminium 1. Like Al, Beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal. The chlorides of both the elements have bridged structure in vapour phase.
Both the chlorides are soluble in organic solvents and are strong Lewis acids. They are used as Friedel Crafts catalysts. Uses of Alkali metals 1.
Beryllium is used in the manufacture of alloys. Copper-beryllium alloys are used in the preparation of high strength springs. Metallic beryllium is used for making windows of X-ray tubes. Magnesium-aluminium alloys are used in air-craft construction. Magnesium powder and ribbon is used in flash powders and bulbs, bombs and signals.
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A suspension of magnesium hydroxide in water called milk of magnesia is used as antacid in medicine. Magnesium carbonate is used in toothpaste. Calcium is used in the extraction of metals from oxides which are difficult to reduce with carbon. Calcium and barium metals are used to remove air from vacuum tubes. Radium salts are used in radiotherapy, for example, in the treatment of cancer Some Important Compounds of Calcium 1.
Properties: On exposure to air, it absorbs moisture and CO2. This process is called slaking of lime. The product obtained is called slaked lime. Because of the basic nature of CaO, it combines with acidic oxides at high temperature to form salts.
10 The s-block elements.pdf
So it is used as a flux in metallurgy. It is an important primary material for the manufacture of cement and is the cheapest form of alkali. It is used in the manufacture of Na2CO3 from caustic soda.
It is used in the purification of sugar and in the manufacture of dye stuffs.