Class 11 chemistry ch 10

Class 11 chemistry chapter 10

S Block Elements Properties

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 known as the alkali metals.

➣   Group 2 include : beryllium, magnesium,calcium, strontium, barium and radium. Except Beryllium they are known as alkalinev

Physical properties- 

a) Large atomic radii: The atomic radii of alkali metals are the largest in their respective periods. These increase as we travel down the group.

b) Large ionic radii: The ionic radii increase as we move down the group due to the addition of a new energy shell with each succeeding element.

c) Low ionization enthalpy: The ionization enthalpies  decrease as we move down the group.The ionization enthalpies of the alkali metals are the lowest due to loosely held s- electron.

d) Hydration enthalpy: It decreases with the increase in ionic radii.The hydration enthalpy of Li ion is the maximum and the hydration enthalpy of Cs ion is the minimum.

e) Oxidation  state:  The  alkali  metals  exhibit  oxidation  state  of  +1  in  their compounds and are strongly electropositive in character. The electropositive character increases from Li to Cs.

f) Metallic character: The metallic character increases down the group.

g) Melting point and boiling point:: The m p and b p  of alkali metals are very low and decrease with increase in atomic number.

h) Nature of bonds formed: These metals form ionic bonds. The ionic character increases as we down the group.

i) Flame colouration: All the alkali metals impart a charactersistic colour to the flame.                              

j) Photoelectric effect: Alkali metals (except Li) exhibits photoelectric effect.

Chemical properties of alkali metals:

 A) Character reduction: with a lower enthalpy of the alkali metals

 Among the group, the reductive character or its response to the invasive state of the group increases.  So Li <Na <K <Rb <Cs.

 B) Interaction with dihydrogen: the alkali metals react with dry hydrogen at about 673 K to form crystalline hydrates of an ionic nature and with a high melting point.

 C) Oxides and hydroxides: alkali metals if otherwise burned in the air

 Compounds, for example, alkali metals as react to a limited amount of oxygen of ordinary oxides (M2O) M = Li, Na, K, Rb, Cs

 D) Interaction with halogens: family members combine with halogens to form the corresponding halides, which are crystalline and ionic solids.

 The reaction of alkali metals with increased halogen from Li to Cs.

 E) Interaction with water: the alkali metals interact with water and other compounds containing acidic hydrogen atoms, such as hydrogen halides, acetylene, etc. to release hydrogen gas.

 F) Solubility in Liquid Ammonia: All alkali metals are dissolved in liquid ammonia, providing deep blue solutions in nature.

 G) Interaction with sulfur and phosphorus: Alkali metals react with sulfur and phosphorus during heating to form sulfides and phosphorus, respectively.

 Land relationship between Li and Al

 Li Mg is mainly the same due to the similarities in the sizes of its atoms and ions.

 The most important agreements are:

 I) Both are very difficult.

 ii) LiOH and Mg (OH) 2 have weak bases.

 3) Carbonate is decomposed during heating to produce CO2.

 4) Both react with nitrogen to give ionic nitride.

 5) Both nitrates are decomposed during heating to give oxides.

 6) Li and Mg do not form solid baking soda.

 vii Due to the covalent nature of LiCl and MgCl2 is soluble in ethanol.

 (Viii) The hydroxides, bicarbonate and fluoride of both Li and Mg are slightly soluble in water.

 The biological significance of Na and K

 I) Sodium ions are involved in the transmission of nerve signals.

 2) Sodium ions also regulate the flow of water through cell membranes and in the transfer of sugars and amino acids to cells.

 2) Potassium ions are the most common cations in cell fluids, as many enzymes are active and involved in glucose oxidation to produce ATP.

 4) Potassium ions with sodium ions are responsible for the transmission of nerve signals.

 5) The functional characteristics of neurons depend on the sodium potassium ion gradient created in the cell.

 Elements of Group 2: Alkaline earth minerals

 A) Atomic radius: The atomic radius of alkaline earth minerals is quite large, although smaller than the corresponding alkali metals and increases in the group.  This is because the atomic radius as a result of the group decreases in the first place increases due to the addition of an additional shell of electrons in each subsequent element.

 (B) Ion beam: The atoms of these elements form divalent ions that show the same direction as their volume increases among the group.

 (C) Ionization enthalpy: The alkaline earth metals have a somewhat lower enthalpy, although they are larger than the corresponding elements in group 1, and this value is reduced to the bottom of the group.

d) hydration ethylene;  Alkaline earth metal ion dehydrating ester decreases as the metal ion size increases in group

 Be2> +> Mg2 +> Ca2 +> Sr2 +> Ba2 +:

 e) state of oxidation;  All members of the family with their complex exhibit a state of +2 oxidation and form bilateral cations (M2 +).

 f) Electricity.  The electrical values ​​of alkaline earth metals are very close to the levels of alkali metals, although slightly higher.

 (g) Metal profile.  Alkaline earth metals have stronger metal bonds than alkali metals in the same period.

 h) melting and boiling point;  The melting and boiling points of these metals are higher than the alkali metals present in the same period.

 (i) Color on fire.  except for beryllium and magnesium, the remaining elements with 9n elements carry color markings to the same fire.  For example,

 Be Mg Ca Sr Ba Ra:

 Brick Red Crimson Grassy Green Crimson

 P) Complicated formation.  Generally, members do not create complexes.  However, smaller ions (Be & Mg Ions) form complexes with electron donor species.

 k) Formation of organometallic compounds.  Beryllium and magnesium form a number of organic metal compounds containing M-C bonds with certain organic compounds.  For example, magnesium reacts with alkyl halide in the presence of dry ethereal to give Grignard reagent.

 l) Declining nature.  Alkaline earth metals are weaker reducing materials than the corresponding alkali metals, which have lower ionization rates and relatively larger atomic sizes.

 j) The reaction with oxygen.  with the exception of Ba և Ra, which produces peroxide (MO2), the remaining metals form normal oxides (MO) in excess oxygen heating.

 n) Reaction with halogens.  Family members combine directly with halogen at appropriate temperatures to form the appropriate halides.

 o) Reaction with water.  The members of this group react less to water than the corresponding alkali metals, because they are less electromotive in nature.

 j) The reaction with hydrogen.  In addition to heating, the members also combine direct heating to form metal hydrides.

 Use of some important compounds.

 Pour cool drink.

 It is used in soap, paper, textiles, oil industry

 Sodium carbonate

 It is used.

 a) in the glass and soap industry

 b) in paper and textile production c) in paints and paints

 d) in metal processing

 e) in the manufacture of sodium compounds, such as borax, caustic soda, sodium phosphate, etc.

 Quick lime.

 It is used.

 a) in the preparation of cement, glass and calcium carbide.

 b) When cleaning sugar

 c) In case of hardening of hard water

 d) As a flow of metal extraction

 Limestone.

 It is used

 a) as building material

 b) in the manufacture of quick lime

 c) For the preparation of Na2CO3 in the Solvay process as it is a source of CO2

 (d) Iron mining

 e) in toothpaste and in certain cosmetics

 Element Cement.

 It is an important building material.  It is used in the construction of concrete and reinforced concrete, stucco, bridges, dams and buildings.

  Plaster in Paris.

 It is used

 a) for making pottery and ceramic molds, etc.

 b) to place the broken bones of the body in surgical dressings

 c) statues, models, decorative materials for making chalkboards.

 The biological significance of Ca և Mg

 i) Magnesium ions are concentrated in animal cells, and calcium ions are concentrated in body fluids outside the cell.

 ii) All enzymes that use ATP in phosphate transfer require magnesium ion as a cofactor.

 iii) In green plants magnesium is found in chlorophyll.

 iv) Calcium and magnesium ions are also needed to transmit signals across nerve fibers.

 v) Calcium ions are important in blood clotting and are necessary to cause muscle contraction.

 vi) Calcium ions also regulate the heart rate.