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Hydration Energy Alkali Metal Alkaline Earth Metals

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Hydration Energy Alkali Metal Alkaline Earth Metals 2- H2O2 changes Cr2O7 ion to CrO5 in an acidic medium, the oxidation state of Cr in CrO5 is (a) +6 (b) +5 (c) -10 (d) +3 Ques) Write balanced chemical equation for the following reaction: – (i) Permanganate ion (MnO4 ) reacts with sulphur dioxide gas in acidic medium to produce Mn2+ and hydrogensulphate ion. Chandni Prince kumar Khushi jha Chanduchandana Chandana s block elements General properties Configuration & Physical state Alkali Alkaline earth Metal metals ● 1 e- in outermost shell ● 2e- in outermost shell ● General formulas ns1 ● General formula ns2 ● All are silvery white ● All are greyish white ● Light soft, malleable ● These are harder than and ductile metals with alkali metals metallic lustre Atomic size Alkali Alkaline earth Metal metals ● Biggest in their ● Smaller than IA group respective period elements ● Size increases from Li ● Size increases to Fr du to addition of gradually from Be to an extra shell. Ra Li < Na < K < Rb < Cs < Be < Mg < Ca < Sr < Ba Fr Ionization potential Alkali Alkaline earth Metal metals ● First I.P. is very less ● First I.P. is higher than because of bigger IA group because of atomic size and only e- smaller atomic size in outermost shell. and completely filled s- orbital (stability) ● Second I.P. is very ● Second I.P. is lesser high because of than IA group. achieving inert gas configuration ● Order of I.P. ● Order of I.P. Li > Na > K > Rb > Cs Be > Mg > Ca > Sr > Ba (1st and 2nd I.P. (1st and 2nd I.P. difference > 16eV) difference < 11eV) Electropositive or metallic character Alkali Alkaline earth Metal metals ● electropositivity ● Their atomic size is ∝1/ionisation smaller than IA group so these are less ● Due to their larger ● Electropositivity size, electron can increases from Be and easily be removed to Ba form M+ ion. ● Electropositivity increases from Li to Cs. Oxidation state Alkali Alkaline earth Metal metals ● These metals shows ● These metals show only +1 only +2 Hydration energy Alkali Alkaline earth Metal metals ● Alkali metals salts are ● Due to smaller ionic generally soluble in size and higher charge water due to hydration density their hydration of cations by water energy is high. molecules. ● Smaller the cation, ● Its decreasing order is greater is the degree of Be+2 > Mg+2 > Ca+2 > Sr+2 its hydration. > Ba+2 Solubility in liquid ammonia Alkali Alkaline earth Metal metals Melting and boiling point Alkali Alkaline earth Metal metals MP & BP ∝ Strength of metallic bond ● Weak interatomic ● Metallic bonds is bonds are due to their stronger than IA group large atomic radii and due to smaller atomic presence of only 1 size and 2e- in valence valence e- hence MP & shell hence MP & BP BP are low are higher ● Order of MP & BP is ● Order of MP & BP is Li > Na > K > Rb > Cs Be > Ca > Sr > Ba > Mg Flame test Alkali Alkaline earth Metal metals ● Alkali metals and their ● Be and Mg atoms, due salts gives to small size, bind their characteristic colour to electrons more bunsen flame. strongly, so are not excited to higher level, hence no flame test. ● The flame energy ● Other elements gives causes an excitation of characteristic colour to the outermost electron flame: which on dropping Ca - Brick red back to ground state Sr - Crimson Red emits absorbed energy as visible light ● Li - Crimson red Anomalous behaviour of first element Diagonal relationship Similarities between Li and Mg Diagonal relationship between beryllium and aluminium Chemical properties Reactivity Alkali Alkaline earth Metal metals Reaction with oxygen Alkali Alkaline earth Metal metals ● Li forms only Li2O ● Alkaline earth metals (Lithium oxide). reacts with O2 to form ‘MO’ type oxides ● Na reacts with O2 to form ● Basic properties peroxide (Na2O2). increases from Be to Ba ● K, Rb and Cs forms MO2 ● CaO2, SrO2, BaO2 Also type oxides (super formed oxides) in excess O2. ● (Li2O) (Na2O2)(KO2, RbO2, CsO2) ● Stability of peroxide and superoxide increase on moving down the group. Halides Alkali Metal Alkaline earth metals ● Reacts with halogen ● Reacts with halogen to to form MX form MX2 ● Ionic properties of MX ● Ionic properties of MX2 increases from LiCl to increases from BeCl2to CsCl BaCl2 ● LiCl is covalent in ● Ba burns in contact with nature. Hence it Cl2 hydrolyses with water ● The melting and boiling while rest are ionic so points always follow the do not hydrolyse trend: fluoride > chloride > bromide > iodide. ● The low solubility of LiF in water is due to its high lattice enthalpy ● The low solubility of CsI is due to smaller hydration enthalpy of its two ions. Carbonates Alkali Alkaline earth Metal metals ● Forms M2CO3 type ● Forms MCO3 type carbonates. Stability carbonates increases down the group. ● Except Li2CO3, all the ● All carbonates carbonates are stable decompose of which towards heat BeCO3 is least stable. Nitrides Alkali Alkaline earth Metal metals ● Only Li reacts directly ● Only be and Mg burns with N2 to form nitride in N2 to give which gives NH3 on M3N2(Be3N2, Mg3N2) reacting with water. ● 6Li + N2 ➝ 2Li3N ● Mg3N2 + 6H2O) ➝ 3Mg(OH)2+ 2NH3 ● Li3N + 3H2O ➝ 3LiOH + NH3 Reaction with hydrogen Alkali Alkaline earth Metal metals ● Alkali metals combine ● Except Be, all the with H2 forming ionic alkaline metals forms hydrides MH2 type hydrides, 2M + H2 ➝ 2MH (MgH2, CaH2, SrH2, BaH2) on heating directly with H2 ● LiH is covalent ● BeH2 is prepared by hydride while others reaction of BeCI2 with are ionic. LiAIH4 2BeCI + LiAIH ➝ 2BeH + ● Electrolysis of fused 2 4 2 LiCI + AICI3 MH gives H2 at anode. Ques) In what ways lithium shows similarities to magnesium in its chemical behaviour? Ques) Why is Li2CO3 decomposed at a lower temperature whereas Na2CO3 at higher temperature ? Ques) Draw the structure of (a) BeCl2 (vapour) (b) BeCl2 (solid). Ques) Write balanced equations for reactions between (a) Na2O2 and water (b) KO2 and water (c) Na2O and CO2. Ques) Which one of the following alkali metals gives mostly hydrated salts? (a) Li (b) Na (c) K (d) Cs Ques) Which one of the alkaline earth metal carbonates is thermally the most stable ? (a) MgCO3 (b) CaCO3 (c) SrCO3 (d) BaCO3 Ques) Alkali metals react with water vigorously to form hydroxides and dihydrogen. Which of the following alkali metals reacts with water least vigorously ? (a) Li (b) Na (c) K (iv) Cs Ques) Find out the oxidation state of sodium in Na2O2. Ques) Beryllium and magnesium do not give colour to flame whereas other alkaline earth metals do so. Why ? Ques) Why are lithium salts commonly hydrated and those of the other alkali ions usually anhydrous? Ques) What happens when (a) Sodium metal is dropped in water? (b) Sodium metal is heated in free supply for air? (c) Sodium peroxide dissolves in water? Ques) Comment on each of the following observations : (a) The mobilities of the alkali metal ions in aqueous solution are Li+ < Na+ < K+ < Rb+ < Cs+ (b) Lithium is the only alkali metal to form a nitride directly. Ques) Which of the alkali metal is having least melting point ? (a) Na (b) K (c) Rb (d) Cs Ques) The alkali metals are low melting. Which of the following alkali metal is expected to melt if the room temperature rises to 30°C ? (a) Na (b) K (c) Rb (d) Cs Ques) The reducing power of a metal depends on various factors. SUggest the factor which makes Li, the strongest reducing agent in aqueous solution. (a) Sublimation enthalpy (b) Ionisation enthalpy (c) Hydration enthalpy (d) Electron-gain enthalpy Ques) Metals form basic hydroxides. Which of the following metal hydroxide is the least basic ? (a) Mg(OH)2 (b) Ca(OH)2 (c) Sr(OH)2 (iv) Ba(OH)2 Ques) The order of decreasing ionisation enthalpy in alkali metals is (a) Na > Li > K > Rb (b) Rb < Na < K < Li (c) Li > Na > K > Rb (d) K < Li < Na < Rb Homework ● Revise entire chapter ● Solve exercise questions and NCERT exemplar Question of the day Ques) Which of the following are the correct reasons for anomalous behaviour of lithium? (a) Exceptionally small size of its atom (b) Its high polarising power (c) It has high degree of hydration (d) Exceptionally low ionisation enthalpy For any queries email me at [email protected] Class 11 Cass 12 2PM 2PM 2PM 2PM 2PM 2PM Mon Tue Wed Thu Fri Sat .
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