Page 1 : lonic Radius, , ¢ Across a period : The ionic radii of, ions having same charge decreases as, , , , , , , , , , , atomic number increases., , ¢ Downa group: Increases, Lit < Na* < Kt < Rb* < Cs*(Cations), , F <Cl <Br <I(Anions), , © Cationic radius < Atomic radius <, Anionic radius (For isoelectronic, species), e Z/e ratio increases, size decreases, and vice-versa., , Atomic Volume, , © Across a period : First decreases and, then increases., , Li, Be, B, C, N, O, EK Ne, (cc/mol)13. 5 5 5 14 11 15 17, ¢ Downa group: Increases, , Li, Na, K, (cc/mol) 13 24 46, , ¢ Across a period : First increases and, then decreases., Na, Mg, Al, Si, PB, S, (g/em3) 1.0 1.7 2.7 23 18 2.1, e Downa group: Decreases, Be(1.8) , Mg(1.7), Highest density solid : Os (22.6), ¢ Highest density liquid : Hg (13.6), , Electron Gain Enthalpy, , © Acrossa period : More negative, Li, Be, B, C, N,, (kJ/mol) -60 +66 -83 -122 +31, O, F, -141 -328, , , , ¢ Down a group: Less negative, H, Li, Na, K, Rb, Cs, (kJ/mol) -73 -60 -53 -48 -47 -46, , , , PERIODICITY IN PROPERTIES, , The basic object of classification is to arrange the facts regarding, elements and their compounds in such a way so that we may, have greatest control over their characteristics with least, possible effort. The repetition of similar physical and chemical, properties of elements after regular intervals is known as, , periodicity in properties., , , , Periodicity in Physical Properties, , Atomic Radius, , ¢ Acrossa period : Decreases, , , , Atomic radius 1/Z .¢¢, Li>Be>B>C>N>O>F, , ) e Downa group: Increases, , H<Li<Na<K<Rb<Cs, , evan der Waals’ radius > Metallic, (e) radius > Covalent radius, , Electronegativity, , © Acrossa period : Increases, Li< Be<B<C<N<O<F, , (e) ¢ Downa group: Decreases, , H>Li>Na>K=Rb>Cs, Fis most electronegative element., , , , @ (tie Character, , e Across a period : First decreases, , (e) and then increases., , , , ¢ Downa group: Increases, , Metallic Character, , (e) ¢ Acrossa period : Decreases, , ¢ Downa group: Increases, , (e) lonisation Enthalpy, , ¢ Acrossa period : Increases, Li<Be>B<C<N>O<F, , O e Downa group: Decreases, , H>Li>Na>K>Rb>Cs, , , , , , , , , , , , , , , , Periodicity in Chemical Properties, , , , ¢ Acrossa period : Increases, NaH < MgH, < AIH; <SiHy, © Downa group : Same, , Reducing Nature, , © Across a period : Decreases, ¢ Downa group: Increases, , Oxidising Nature, , © Acrossa period : Increases, ¢ Downa group: Decreases, , Strength of Oxyacids, , © Acrossa period : Increases, H3BO3 <H,CO3< HNO;, , e¢ Downa group: Decreases, , HNO3>H3PO4>H3AsO4, , © Acrossa period : Increases, Na,O < MgO < Al,O3 < SiO) < P2O5, <SO3<Cl,07, , e Downa group: Decreases, N03 > P03, , Acidity of Hydrides, , © Acrossa period : Increases, CH, <NH3<H,0<HF, ¢ Downa group: Increases, , , , , , , , , , HE<HCl<HBr< HI, , Melting and Boiling Points, , ¢ Acrossa period: M.pt. and B.pt. first increase and then decrease., , Element: Na Mg Al Si, , M.pt. (K):370.8 924 933 1693 317 392, , B.pt.(K) : 1165 1396 2075 2815 557 717.6, ¢ Downa group : They do show regular gradation but pattern of variation is different in, , different groups., Element: Li Na K, , Rb Cs, M.pt.(K): 454 370.8 335 312 302, , , , B.pt.(K) : 1609 1165 1063 973 943