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2613 s and p – Block Elements13.2 GROUP 1 ELEMENTS13.2.1 Atomic and Physical Properties of the Group 1 Elements (AlkaliMetals)This section explores the trends in someatomic and physical properties of the Group 1elements - lithium, sodium, potassium, rubidiumand caesium. You will find separate sectionsbelow covering the trends in atomic radius, firstionization energy, electronegativity, melting andboiling points, and density.Trends in Atomic RadiusAs we move from lithium to caesium, an extrashell of electrons is added to each element. The addition of an extra shell increases the atomicvolume. We find therefore, that there is an increase of atomic and ionic radii (of M + ions) as wemove from lithium to caesium.Table 13.3 Some Physical Properties of Alkali MetalsProperty Li Na K Rb CsAtomic weight 6.94 22.99 39.1 25.47 132.91Atomic volume 12.97 23.63 45.36 55.8 69.95Atomic (i.e. metallic radius forcoordination number 121.55 1.9 2.35 2.46 2.6covalent radius 1.23 1.54 2.03 2.16 2.36Ionic radius of M+ ions 0.6 0.95 1.33 1.48 1.69Melting point 180.5 97.8 63.7 38.9 28.7Boiling point 1330 892 760 688 670Ionisation energies (kJ/mol)(I1)520.3 495.8 418.9 403.0 375.7I2Fig. 13.22 Atomic Radii of the Group 1Elements7298.1 4562.4 3051.4 2633.0 2230.0Standard oxidation potential 3.04 2.71 2.99 2.99 2.99Sublimation energy (eV/ion) 1.7472 1.2432 1.032 0.984 0.9024Hydration energy (eV/ion) 5.904 3.792 3.6955 3.36 0.624Electronegativity 1 0.9 0.8 0.8 0.7Colour of the flameGoldenCrimson redViolet Violet VioletyellowHeat of atomisation at 25C(eV/atm)1.7472 1.2432 1.032 0.984 0.9024Ionic conduction of M+ ion 33.5 43.5 64.6 67.5 63Trends in First Ionization EnergyFirst ionization energy is the energy needed to remove the most loosely held electron fromeach of one mole of gaseous atoms to make one mole of singly charged gaseous ions - in otherwords, for 1 mole of this process:
13 s and p – Block ElementsNotice that first ionization energy falls as yougo down the group. We know that alkali metal haveonly one electron in their outermost shell (ns 1electron). This ns 1 electron is so weakly held withthe nucleus that it can be removed very easily. Alkalimetals therefore have low ionisation energies.As the distance of ns 1 electron from thenucleus increases on moving from Li to Cs itsremoval becomes more and more easy as we proceed from Li to Cs i.e. the amount of energy(ionization energy) used in the removal of ns 1 electron is maximum in case of energies of alkalimetals go on decreasing from Li to Cs as shown in table 13.3.The second ionisation energies are fairly high, since the loss of the second electron fromM+ cation which has a noble gas configuration is quite difficult.Trends in ElectronegativityElectronegativity is a measure of the tendency of anatom to attract a bonding pair of electrons. It isusually measured on the Pauling scale, on which themost electronegative element (fluorine) is given anelectronegativity of 4.0.We have seen that the outer electron (i.e. ns 1electron) of the atom of alkali metals is loosely heldwith the nucleus and hence it can be easily excitedto the higher energy levels even by a small amountof heat energy. During the excitation process the electron absorbs some energy and when thisexcited electron comes back to its original position, it gives out absorbed energy in the form oflight in visible region of the electromagnetic. Since the amount of energy absorbed during theexcitation process is different in different atoms, different colours are imparted by the atoms tothe flame. The property of alkali metals togive colouration in the burner flame hasbeen used to detect their presence in saltsby a test, known as flame test.Trends in Melting and Boiling PointsYou will see that both the meltingpoints and boiling points fall as you go downthe Group.Fig. 13.23 First Ionization Energy ofthe Group 1 elementsFig 13.24 Electronegativties of the Group 1elementsThe melting and boiling points are very lowbecause of the presence of weak inner Fig 13.25: Melting and Boiling Points of the Group 1atomic bonds in the solid state of the alkalielementsmetals. These bonds are due to their atomicradii and mainly due to the their electronic configuration having a single valence electrons as27
Page 1: Textbook ofChemistryGrade 12
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15 Organic Compounds1053. Melting a
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15 Organic CompoundsNitrileMethyle
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15 Organic Compounds113C) Detection
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16 Hydrocarbons11716.1 TYPES OF HYD
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16 Hydrocarbons119orororQuick Quiz1
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16 Hydrocarbons1213-Ethyl-2,3,5-tri
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16 Hydrocarbons123(b) Alkanes are n
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16 Hydrocarbons125II. CycloalkanesA
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16 Hydrocarbons127shown again below
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16 Hydrocarbons129Activity1. Name t
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16 Hydrocarbons1312. Dehydrohalogen
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16 Hydrocarbons133HydrationAddition
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16 Hydrocarbons135PolymerizationPol
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16 Hydrocarbons137benzeneconjugated
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16 Hydrocarbons13916.6.2 Carbon-Bas
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16 Hydrocarbons141(+)Tartaric Acid:
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16 Hydrocarbons143No geometrical is
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16 Hydrocarbons1451) MetamerismThis
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16 Hydrocarbons147(b)(c)(d)(e)16.7.
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16 Hydrocarbons149terminal alkyne p
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16 Hydrocarbons151BrominationChlori
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16 Hydrocarbons153CumeneDisubstitut
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16 Hydrocarbons159(c) Addition of H
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16 Hydrocarbons161Explanation and E
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16 Hydrocarbons163SulfonationThe in
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16 Hydrocarbons167On the other hand
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16 Hydrocarbons169SOCIETY, TECHNOLO
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16 Hydrocarbons171Exercise1. The mo
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17 Alkyl Halides and Amines175(ii)
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17 Alkyl Halides and Aminesiv. Tert
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