15.1 rest of the members and shows diagonal

15.1 Alkaline Earth metals and their properties. Group 2 elements you will: ????????? ?????????????? ????????? ?????????? ??????? ????????? 2 (II) ??????; ????????? ?????????????? ????????? ?????????? ??????? ????????? 2 (II) ??????;The group 2 elements comprise beryllium, magnesium, calcium, strontium, barium and radium. These (except beryllium) are known as alkaline earth metals. The first element beryllium differs from the rest of the members and shows diagonal relationship to aluminium. Electron configuration These elements have two electrons in the s-orbital of the valence shell. Their general electronic configuration may be represented as noble gas ns2 . Like alkali metals, the compounds of these elements are also predominantly ionic.Be 1s2 2s2Mg 1s2 2s2 2p6 3s2Ca1s2 2s2 2p6 3s2 3p6 4s2Sr1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2Ba1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2 or Xe 6s2RaRn7s2 Atomic and Ionic RadiiThe atomic and ionic radii of the alkaline earth metals are smaller than those of the corresponding alkali metals in the same periods. This is due to the increased nuclear charge in these elements. Within the group, the atomic and ionic radii increase with increase in atomic number. Atomic and Physical Properties of the Alkaline Earth MetalsPropertiesBeMgCaSrBaRaAtomic number41220385688Atomic mass9.0124.3140.0887.62137.33226.03Electron configurationHe2s2Ne3s2Ar4s2Kr5s2Xe6s2Rn7s2Metallic radius, pm112160197215222(220)Ionic radius M2+, pm3172100118135148Melting point, ? 1287650842777727700Boiling point, ? 247110901484138218971140Density, g/cm31.841.741.552.633.59(5.5)The alkaline earth metals have low ionization enthalpies due to fairly large size of the atoms.Since the atomic size increases down the group, their ionization enthalpy decreases. The hydration enthalpies of alkaline earth metal ions decrease with increase in ionic size down the group:Be2+> Mg2+> Ca2+> Sr2+> Ba2+     Physical Properties The alkaline earth metals, in general, are silvery white, lustrous and relatively soft but harder than the alkali metals. Beryllium and magnesium appear to be somewhat greyish. The melting and boiling points of these metals are higher than the corresponding alkali metals due to smaller sizes. The trend is, however, not systematic. Because of the low ionisation enthalpies, they are strongly electropositive in nature. The electropositive character increases down the group from Be to Ba. Calcium, strontium and barium impart characteristic brick red, crimson and apple green coloursrespectively to the flame. In flame the electrons are excited to higher energy levels and when they drop back to the ground state, energy is emitted in the form of visible light. The electrons in beryllium and magnesium are too strongly bound to get excited by flame. Hence, these elements do not impart any colour to the flame. The flame test for Ca, Sr and Ba is helpful in their detection in qualitative analysis and estimation by flame photometry. The alkaline earth metals like those of alkali metals have high electrical and thermal conductivities which are typical characteristics of metals.   Magnesium metal 379613968 Chemical PropertiesThe alkaline earth metals are less reactive than the alkali metals. The reactivity of these elements increases on going down the group.All the members of the group are covered by their oxides when they are exposed to air. The alkaline earth metals burn in air with bright flame. As a result of burning in air, their oxides and nitrides are formed. The compounds of all the alkaline earth metals are similar in composition, they all form oxides (MO), hydroxides (M(OH)2), carbonates (MCO3), sulfates (MSO4), and other compounds (M is any alkaline earth metal). The alkaline earth metals are strong oxidizing agents. Activity of the metals increases from Be to Ba. The elements Ca, Sr and Ba undergo reaction with water easily, whereas the reaction of Be and Mg with water is difficult. In order to increase the activity of Mg metal, the Mg metal is transformed into an amalgam. Thus, since the oxide of Mg is not formed on the surface of the metal, its activity increases in the chemical reactions.1. All alkaline earth metals, except Be, react with H2 gas in hot medium to produce hydrides, like alkali metals:Mg + H2 ? MgH2Only CaH2, of all hydrides formed, reacts with water by releasing heat:CaH2 + 2H2O ? Ca(OH)2 + 2H2 2. Ca, Sr and Ba react with water, like alkali metals, at room temperature to produce metal hydroxidesand hydrogen gas:Ca + 2H2O ? Ca(OH)2 + H2Magnesium metal reacts slowly with boiling water. The reaction of beryllium with water is very difficult.3.   The metals reduce O2, N2  to form the oxides and nitrides: 2Sr(s) + O2(g)  ? 2SrO(S)        3Sr + N2 ? Sr3N2Ba also forms  the  peroxide, BaO2. These oxides are slightly soluble in water and solutions of these oxides, except BeO, show basic properties.4. All alkaline earth metals give direct reactions with halogens to produce metal halides. Ba + Cl2 ? BaCl25. The alkaline earth metals readily react with acids liberating hydrogen gas.Be + 2HCl ? BeCl2+ H2The reaction of Mg with nitric acid HNO3 produces N2O, NO2 gases:4Mg + 10HNO3(dilut)? 4Mg(NO3)2 + N2O + 5H2O6. All oxides and hydroxides of alkaline earth metals, except beryllium, show basic properties whereas Be metal, its oxide and its hydroxide show amphoteric properties. In other word, Be, BeO and Be(OH)2 show amphoteric properties. Be(s) + 2HCl(aq)  ?  BeCl2+ H2(g)Be(s) + 2NaOH(aq) + 2H2O(l) ? Na2Be(OH)4(aq) + H2(g) Burning of calcium  714294448 UsesMetallic beryllium is used to prepare some special alloys. About 2% beryllium in copper produces a hard alloy especially suited for use in springs. The metal is used in making glass for X-ray tubes, so x-rays readily penetrate elements with low atomic number. Beryllium has the mechanical properties of a very light element. Beryllium alloys   190592564Since magnesium is a light metal, it is used in the production of planes, missiles and some light household items. In alloys, it is used to increase the hardness, durability and resistance to corrosion. The light produced by the burning of magnesium tape with oxygen is used as a flash in photography. Mg is also used as an additive in rocket fuels and signal rockets. Mg(OH)2, milk of magnesia is used as a stomach antacid.Magnesium alloy wheel 325493813The compounds of calcium, hydroxides, carbonates and oxides, are widely used as construction materials and as bleaching agents. Calcium oxide is the main compound in the production of some chemicals, steel, glass, paper and sugar. Calcium carbide (CaC2) is used to produce acetylene gas for welding. Acetylene gas produced from calcium carbide. 683578501Strontium has many important applications in industry. The salts of strontium are used in signal rockets and fireworks to produce red light.600497582   Signal rocketsBarium is used as a gas absorbent in vacuum tubes. Since the alloys of barium with nickel donate electrons by heating they are used in vacuum tubes and in ignitors. Barium nitrate (Ba(NO3)2) and barium chlorate (Ba(ClO3)2) are used to obtain green light in fireworks. BaSO4 (barium meal) is used to take the photos of stomach and intestines because, like all elements with large atomic number, it does not allow X-rays to pass. In fact, the Ba2+ ion is rather toxic, but since the solubility of BaSO4 in water is very low, its poisonous effect disappears. 283532912  X-ray image of abdomenRadium is used in self luminous paints and in radiotherapy and as a neutron source. 426938098   Radiotherapy treatment ddddd

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