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Doc Brown's Chemistry  Advanced Level Inorganic Chemistry Periodic Table Revision Notes

Part 6.4 Revising important general trends down a Group

A discussion of group trends in terms of ionisation energies, melting points, boiling points, atomic radii, ionic radii, metallic/non-metallic character of the element, electronegativity, densities, relative electrical conductivities, oxidation states, formulae of oxides, chlorides, character of chloride and acid-base character of oxide. There is a further discussion of the diagonal relationship between pairs of elements in adjacent groups.

For non-A level students (c) doc b KS4 Science GCSE/IGCSE Periodic Table notes links

INORGANIC Part 6 Period 4 survey & group trends page sub-index: 6.1 Survey of Period 4 elements * 6.2 Period 4 trends in physical properties * 6.3 Period 4 trends in bonding, formulae and oxidation state * 6.4 Important element trends down a Group

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots


6.4 A summary of important physical and chemical trends down a Group


GROUP DATA TABLES - data aligned down the group

z = at. no., cond'y = conductivity, config. = configuration, oxidation states are numerically equal to valencies

M = metal, SM = semi-metal (metalloid), NM = non-metallic element


Group 1 Alkali Metals

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical cond'y ox. state oxide formulae chloride formulae
oC K oC K
3Li lithium M [He]2s1 181 454 1347 1620 0.98 152 513 0.5 0.108 +1 Li2O LiCl
11Na sodium M [Ne]3s1 98 371 883 1156 0.93 186 496 1.0 0.218 +1 Na2O, Na2O2 NaCl
19K potassium M [Ar]4s1 64 337 774 1047 0.82 231 419 0.8 0.143 +1 K2O, K2O2, KO2 KCl
37Rb rubidium M [Kr]5s1 39 312 688 961 0.82 244 403 1.5 0.080 +1 Rb2O, Rb2O2, RbO2 RbCl
55Cs caesium M [Xe]6s1 29 302 679 952 0.79 265 376 1.9 0.053 +1 Cs2O, Cs2O2, CsO2 CsCl
87Fr francium M [Rn]7s1 27 300 677 950 0.70 270 400 2.0 0.014 +1 assumed Fr2O, Fr2O2, FrO2 assumed FrCl
  • One of the most consistent sets of data for any group of the periodic table, helped by the fact they are all metals.

  • The melting/boiling points, electronegativity, 1st ionisation energy and electrical conductivity decrease down the group.

  • The atomic radius and density increase down the group.

  • The formulae are perfectly consistent with what you might expect from the principles of the Periodic Table e.g. the chlorides, the metal having the only possible oxidation state of +1 (valency 1).

  • Down the group the peroxide (M2O2) and the 'superoxide' (MO2) become more stable with respect to the expected oxide formula (M2O).

  • 7 Detailed advanced level chemistry notes s-block Group 1 Alkali Metals

  • Explanation of general group trends down the groups of the periodic table (end of this page)

Advanced Inorganic Chemistry Page Index and Links


 

Group 2 Alkaline Earth Metals

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity ox. state oxide formulae chloride formulae
oC K oC K
4Be beryllium M [He]2s2 1278 1551 2970 3243 1.57 111 900 1.8 0.250 +2 BeO BeCl2
12Mg magnesium M [Ne]3s2 649 922 1090 1363 1.31 160 738 1.7 0.224 +2 MgO, MgO2 MgCl2
20Ca calcium M [Ar]4s2 839 1112 1484 1757 1.00 197 590 1.6 0.218 +2 CaO, CaO2 CaCl2
38Sr strontium M [Kr]5s2 769 1042 1384 1657 0.95 215 550 2.5 0.043 +2 SrO, SrO2 SrCl2
56Ba barium M [Xe]6s2 729 1002 1637 1910 0.89 215 503 3.6 0.016 +2 BaO, BaO2 BaCl2
88Ra radium M [Rn]7s2 700 973 1140 1413 0.89 223 509 5.0 0.010 +2 assumed RaO, RaO2 assumed RaCl2

Advanced Inorganic Chemistry Page Index and Links


 

Group 3/13

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity ox. states oxide formulae chloride formulae
oC K oC K
5B boron NM [He]2s22p1 2300 2573 3659 3932 2.04 90 (cov) 801 2.3 <0.001 +3 B2O3 BCl3
13Al aluminium M [Ne]3s23p1 661 934 2467 2740 1.61 143 577 2.7 0.382 +3 Al2O3 AlCl3
31Ga gallium M [Ar]3d104s24p1 30 303 2400 2673 1.81 153 579 5.9 0.058 +1, +3 Ga2O3 GaCl3
49In indium M [Kr]4d105s25p1 156 429 2080 2353 1.78 163 558 7.3 0.111 +1, +3 In2O3 InCl3
81Tl thallium M [Xe]4f145d106s26p1 304 577 1457 1730 1.80 170 589 11.9 0.055 +1, +3 Tl2O3 TlCl3

Advanced Inorganic Chemistry Page Index and Links


 

Group 4/14

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic covalent or metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity ox. states oxide formulae chloride formulae
oC K oC K
6C carbon NM [He]2s22p2 3547 3820 4827 5100 2.55 77 (cov) 1086 2.3 0.001 +2, +4 CO, CO2 CCl4
14Si silicon NM [Ne]3s23p2 1410 1683 2355 2628 1.90 117 (cov) 786 2.3 <0.001 +4 SiO2 SiCl4
32Ge germanium SM [Ar]3d104s24p2 937 1210 2830 3103 2.01 139 (met) 762 5.3 <0.001 +2, +4 GeO, GeO2 GeCl2, GeCl4
50Sn tin M [Kr]4d105s25p2 232 505 2270 2543 1.96 158 (met) 709 5.8 0.088 +2, +4 SnO, SnO2 SnCl2, SnCl4
82Pb lead M [Xe]4f145d106s26p2 328 601 1740 2013 2.33 175 (met) 716 11.4 0.046 +2, +4 PbO, Pb3O4, PbO2 PbCl2, PbCl4

Advanced Inorganic Chemistry Page Index and Links


 

Group 5/15

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic covalent or metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity Ox. states oxide formulae chloride formulae
oC K oC K
7N nitrogen NM [He]2s22p3 -210 63 -196 77 3.04 75 (cov) 1402 <0.1 <0.001 -3 to +5 N2O, NO, N2O3, NO2, N2O5 NCl3
15P phosphorus NM [Ne]3s23p3 44 317 280 553 2.19 110 (cov) 1060 1.8 <0.001 +3, +5 P4O6, P4O10 PCl3, PCl5
33As arsenic SM [Ar]3d104s24p3 sub sub sub sub 2.18 122 (cov) 947 5.8 0.029 +3, +5 As4O6, As4O10 AsCl3
51Sb antimony SM [Kr]4d105s25p3 631 904 1635 1908 2.05 143 (cov), 161 (met) 834 6.7 0.026 +3, +5 Sb2O3 SbCl3
83Bi bismuth M [Xe]4f145d106s26p3 272 545 1560 1833 2.02 182 (met) 703 9.7 0.009 +3, +5 Bi2O3 BiCl3

Advanced Inorganic Chemistry Page Index and Links


 

Group 6/16

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic covalent or metallic radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity Ox. state oxide formulae chloride formulae
oC K oC K
8O oxygen NM [He]2s22p4 -218 55 -183 90 3.44 73 (cov) 1314 <0.1 <0.001 -1, -2 O2 OCl2
16S sulphur NM [Ne]3s23p4 117 390 445 718 2.58 102 (cov) 1000 2.1 <0.001 -2, +2, +4, +6 SO2, SO3 S2Cl2, SCl2, SCl4
34Se selenium SM [Ar]3d104s24p4 217 490 685 958 2.55 117 (cov), 190 (met) 941 4.8 0.080 +2, +4, +6 SeO2, SeO3 Se2Cl2, SeCl4
52Te tellurium SM [Kr]4d105s25p4 450 723 990 1263 2.10 135 (cov), 210 (met) 869 6.2 <0.001 +4, +6 TeO, TeO2, TeO3 TeCl2, TeCl4
84Po polonium M [Xe]4f145d106s26p4 254 527 962 1235 2.00 167 812 9.3 0.020 +2, +4, +6 PoO, PoO2 PoCl2, PoCl4

Advanced Inorganic Chemistry Page Index and Links


 

Group 7/17 The Halogens

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic covalent radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity ox. formulae oxide formula chloride formulae
oC K oC K
9F fluorine NM [He]2s22p5 -219 54 -188 85 3.98 64 1681 <0.1 <0.001 -1 F2O FCl
17Cl chlorine NM [Ne]3s23p5 -101 172 -34 239 3.16 99 1251 <0.1 <0.001 -1, +1, +3, +4, +5, +7 Cl2O, ClO2, Cl2O6, Cl2O7 Cl2
35Br bromine NM [Ar]3d104s24p5 -7 266 59 332 2.96 114 1140 3.1 <0.001 -1, +1, +3, +4, +5, +7 Br2O, BrO2, BrO3 BrCl
53I iodine NM [Kr]4d105s25p5 114 387 184 457 2.66 133 1010 4.9 <0.001 -1, +1, +3, +5, +7 I2O4, I2O5, I2O7 ICl
85At astatine NM [Xe]4f145d106s26p5 302 575 337 610 2.20 140 930 7.5 <0.001 -1, +1, +3, +5, +7 ??? na na

Advanced Inorganic Chemistry Page Index and Links


 

Group 0/18 The Noble Gases

ZElement   Electron configuration Melting Point Boiling Point Pauling electro-negativity Atomic covalent radius pm 1st  ionisation energy kJ/mol Density g/cm3 Relative electrical conductivity Ox. state oxide formulae chloride formulae
oC K oC K
2He helium NM 1s2 -272 1 -269 4 5.50 49 2372 <0.1 <0.001 - na na
10Ne neon NM [He]2s22p6 -249 24 -246 27 4.84 51 2081 <0.1 <0.001 - na na
18Ar argon NM [Ne]3s23p6 -189 84 -186 87 3.20 94 1520 <0.1 <0.001 - na na
36Kr krypton NM [Ar]3d104s24p6 -157 116 -152 121 3.20 109 1520 <0.1 <0.001 +2 na na
54Xe xenon NM [Kr]4d105s25p6 -112 161 -105 168 2.40 130 1170 <0.1 <0.001 +2, +4, +6, +8 XeO3, XeO4 na
86Rn radon NM [Xe]4f145d106s26p6 -71 202 -62 211 2.10 136 1037 <0.1 <0.001 - na na

Advanced Inorganic Chemistry Page Index and Links


 

Summary and general arguments for group trends

  • 1st Ionisation enthalpy of an element: ΔH for the process X(g) ==> X+(g) + e- 

    • The 1st ionisation energy decreases down a group as the outer electrons are increasingly less strongly held.

    • As you go down the group from one element down to the next, the outer electron is further and further from the nucleus because of the extra full shell of electrons due to the change in period. The outer electrons are also shielded by this extra full shell of negative charge from the effect of the positive nucleus. The effective nuclear charge can be considered to be equal to the number of outer electrons and this is effectively the same for all the elements in a group.

    • However, it is spread over an increasingly larger 'outer surface', down the group, so steadily reducing the electric field effect of the positive nucleus attracting the outer negative electrons. Therefore the outer electron is less and less strongly held by the nucleus and this combination of factors means the outer electron is increasingly more easily lost, (e.g. the M+ ion more easily formed), and so less energy is needed remove it.

    • The 'diluting effect' of the increasing outer surface area on the strength of the electron attracting electric field effect, outweighs the increase in atomic/proton number down the group.

  • Atomic radius of an element

    • Can be defined as volume within which 95% of the electron charge exists on a time averaged basis.

    • Atomic radius increases down the group as an extra inner shell of electrons is added per period.

    • The argument is almost identical to that for ionisation energy above.

    • As you go from one period to another an extra full inner shell of electrons is added and the outer electrons are increasingly further away, increasingly shielded by more filled inner shells and hence less strongly attracted to the nucleus

    • Therefore the volume occupied by the electrons expands as you go down the group.

  • Ionic radii

    • The ionic radius increases down the group as an extra inner shell of electrons is added per period.

    • For the trend we assume all the ions have the same charge for the same group e.g. Gp1/2 form M+/M2+ ions or Gp7 form X- ions and the argument is identical to that for the atomic radius increase.

    • The reasons are identical to the argument set out for atomic radius.

  • Metallic or non-metallic character of an element:

    • Elements tend to get more metallic down a group.

    • The trend doesn't show up strongly in Gps 1, 2 (both all metals) and 7 Halogens (all non-metals), but in Gp 4 you start with non-metallic carbon at the top and very metallic lead at the bottom.

    • The principal reason is the lowering of ionisation energies as you descend the group.

  • Electronegativity of an element (usually the Pauling scale)

    • The power (electric field effect) of an atom to attract electron charge towards it, in the context of the electrons of a covalent bond linking it to another atom.

    • Electronegativity decreases down a group.

      • The reason are essentially the same as the lowering of the 1st ionisation energy due to increase in atomic radius and the outer electrons being less strongly held, even in the context of a bonding situation.

      • So, in this case, the arguments support the notion that the nucleus has a lesser and lesser effect in attracting the outer electrons including a pair of bonding electrons.

      • This weakens the bond and less thermal energy is required effect a change of state melting or boiling.

  • Melting points and boiling points of elements:

    • Trends can be a bit complicated due to significant structural changes from one element to another in the same group.

    • However for Groups 1 and 2 the general trend is for melting points and boiling points to decrease down the group.

      • As the atomic radii increase down the group, the positive nucleus to delocalised distance increases.

      • This decreases the electrical attractive force between the immobile ions in the metal lattice and the free mobile delocalised electrons.

    • For Groups 7/17 Halogens and Group 0/18 Noble Gases the melting points and boiling points steadily increase down the group.

    • As the molecule gets bigger with more electrons, the Van der Waals forces (transient dipole - induced dipole) increase in strength so more energy is required to overcome them i.e. a higher thermal energy - increased temperature.

  • Advanced Inorganic Chemistry Page Index and LinksRelative electrical conductivity:

    • Generally increases as the metallic character increases, which can, as in the case of Group 5,

  • Density

    • Generally increases as the metallic character increases, which can, as in the case of Group 5,

    • However, even if they are all metals (Groups 1& 2) or all non-metals (Groups 7/17 & 0/18) generally speaking density does increase down a group.

  • Oxidation states

    • In terms of the general principles of the Periodic Table i.e. group similarity, you would expect all the elements to exhibit the same oxidation states in their compounds, and generally this is true except for oxygen in Group 6/16 and fluorine in Group 7/17.

    • However, down a group you can get a significant change in the relative stabilities of different oxidation states.

      • This is can be seen as increasing stability of a lower oxidation state with respect to a higher oxidation state e.g.

        • In Group 3/13 the +1 state becomes more stable with respect to the +3 state

        • In Group 4/14 the +2 state becomes more stable with respect to the +4 state

        • In Group 4/14 the +2 state becomes more stable with respect to the +4 state

  • The character of the chlorides

    • For Groups 1 and 2 the halides become more ionic as the difference in electronegativity increases and the steadily decreasing polarising power of the cation as its radius increases down the group.

    • Trends become complicated if two different oxidation states are involved.

  • The character of the oxides

    • For Groups 1 and 2 the halides become more ionic as the difference in electronegativity increases and the steadily decreasing polarising power of the cation as its radius increases down the group.

    • Trends become complicated if two different oxidation states are involved.

  • The acid-base character of oxides

    • More importantly, oxides get more basic or less acidic down a group.

      • e.g. Group 5/15

      • At the top of the group the oxides of nitrogen and phosphorus are strongly acidic,

      • arsenic(III) oxide is weakly acidic,

      • antimony(III) oxide is amphoteric,

      • and bismuth(III) oxide at the bottom of the group is basic.

  • -

Advanced Inorganic Chemistry Page Index and Links


Diagrammatic summary of three important Periodic Table Trends

and the so-called 'diagonal relationship of some elements'

  • In the periodic table

    • from left to right across a period

      • 1st ionisation energy increases

      • atomic radius decreases

      • electronegativity increases

      • decrease in metallic character

      • oxide becomes less basic (i.e. more acidic)

      • ease of formation of positive ion decreases

  • Advanced Inorganic Chemistry Page Index and LinksDown a group of the Periodic Table:

    • 1st ionisation energy decreases

    • atomic radius increases

    • electronegativity decreases

    • increase in metallic character

    • oxide becomes more basic

    • ease of formation of positive ion increases

  • As you can see, the trends across a period are the opposite of the trends down a group.

  • These two trends tend to cancel each other out so that elements which are diagonal with respect to each other (top left to bottom right) sometimes show some similarities when considering some of the elements of periods 1 and 2.

  • This phenomenon is explained in terms of the horizontal and vertical relationships described above.

    • From left to right the decrease in size of the atom or positive ion is accompanied by an increase in electronegativity.

    • On descending a group the increase in size of the atom or positive ion is accompanied by a decrease in electronegativity

  • Examples of the so-called diagonal relationship

    • Lithium and magnesium

      • Atomic radii: Li 152 pm, Mg 160 pm

      • Ionic radii: Li+ 78 pm, Mg2+ 78pm

      • Boiling point: Li 1347oC, Mg 1090oC, other group 1 metals much lower

      • Electronegativity: Li 1.0, Mg 1.3

      • Lithium is much harder than the other alkali metals, more like magnesium

      • Lithium does not form a peroxide, unlike other alkali metals, neither does magnesium

      • Lithium carbonate readily thermally decomposes to give the oxide, as does magnesium oxide, but the other alkali metal carbonates do not readily decompose on heating.

      • Lithium hydroxide is sparingly soluble, as is magnesium hydroxide, but sodium hydroxide etc. are very soluble in water.

      • Lithium carbonate is sparingly soluble, as is magnesium carbonate, but sodium carbonate etc. are quite soluble.

      • Lithium nitrate(V) thermally decompose to give the oxide, as does magnesium nitrate(V), but the other group 1 nitrates leave a residue of the nitrate(III) salt (nitrite salt) on strong heating.

      • Lithium forms a nitride (Li3N) as does magnesium (Mg3N2), but the other group 1 alkali metals do not.

    • Beryllium and aluminium

      • Atomic radii: Be 111 pm, Al 143 pm

      • Ionic radii: Be2+ 31pm, Al3+ 50 pm

      • Boiling point: Be 2477oC, Al 2467oC

      • Oxides: BeO and Al2O3 are both amphoteric, rest of Group 2 oxides are only basic.

      • Reaction with dilute acids: Be and Al are fairly resistant unless amalgamated or very finely divided, other Group 2 metals readily react.

      • Reaction with conc. nitric(V) acid: Be and Al are rendered passive, rest of Group 2 metals readily form salts.

    • Boron and silicon

      • Atomic radii: B 88 pm, Si 117 pm

      • Both elements exist as a non-metallic giant covalent 3D lattice.

      • Both form a weakly acidic oxide.

      • ---

  • However, it should be noted that these diagonal similarities are 'weaker' than their similarities to the other elements in their respective groups.


Advanced Inorganic Chemistry Page Index and Links

WHAT NEXT?

See also 4.1 Period 2 Survey of the individual elements, 4.2 Period 2 element trends and explanations of physical properties * 4.3 Period 2 element trends in bonding, structure, oxidation state, formulae & reactions, 5.1 Period 3 survey of elements, 5.2 Period 3 element trends & explanations of physical properties, 5.3 Period 3 element trends in bonding, structure, oxidation state, formulae & reactions, 6.1 Survey of Period 4 elements, 6.2 Period 4 trends in physical properties, 6.3 Period 4 trends in bonding, formulae and oxidation state

INORGANIC Part 6 Period 4 survey & group trends page sub-index: 6.1 Survey of Period 4 elements * 6.2 Period 4 trends in physical properties * 6.3 Period 4 trends in bonding, formulae and oxidation state * 6.4 Important element trends down a Group

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s-block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p-block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots

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