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Periodic table Period 4 elements potassium-krypton: explaining physical property trends  Advanced inorganic chemistry

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

Part 6.2 Period 4 trends AND explanations of physical properties

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All my periodic table advanced A level chemistry revision notes

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GCSE Level periodic table revision notes

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Data, graphs (plots), trends and explanations of the physical properties of the elements of Period 4 of the Period Table.

The first ionisation energy, atomic radius, Pauling electronegativity, melting point, boiling point, electrical conductivity and density trends are all plotted, discussed and explained.

DATA TABLE of physical properties of period 4 elements potassium to sodium to krypton

(1) Variation of 1st Ionisation enthalpy across Period 4

(2) Variation of atomic radius across period 4

(3) Variation of electronegativity across Period 4 (Pauling scale)

(4) Variation of melting points and boiling points across Period 4

(5) Variation of relative electrical conductivity across Period 4

(6) Variation of density across Period 4

6.2 Period 4 Trends in physical properties

DATA TABLE of physical properties of the elements sodium to argon

The data for Period 4 is NOT shown from left to right, due to the number of columns required!

Z symbol Name mpt/oC mpt/K bpt/oC bpt/K Pauling electro–negativity 1st ionisation energy kJ/mol Atomic radius pm Relative electrical conductivity Density g/cm3
19 K potassium 64 337 774 1047 0.82 419 231 0.143 0.8
20 Ca calcium 839 1112 1484 1757 1.00 590 197 0.218 1.6
21 Sc scandium 1541 1814 2836 3109 1.36 631 161 0.015 3.0
22 Ti titanium 1668 1941 3287 3650 1.54 658 145 0.024 4.5
23 V vanadium 1910 2183 3380 3653 1.63 650 132 0.040 6.1
24 Cr chromium 1857 2130 2672 2945 1.66 653 125 0.078 7.2
25 Mn manganese 1246 1519 1962 2235 1.55 717 124 0.054 7.4
26 Fe iron 1538 1811 2861 3134 1.83 759 124 0.100 7.9
27 Co cobalt 1495 1768 2870 3143 1.88 760 125 0.160 8.9
28 Ni nickel 1455 1728 2730 3003 1.91 737 125 0.145 8.9
29 Cu copper 1083 1356 2567 2840 1.90 745 128 0.593 9.0
30 Zn zinc 420 693 907 1180 1.65 906 133 0.167 7.1
31 Ga gallium 30 303 2400 2673 1.81 579 122 0.058 5.9
32 Ge germanium 937 1210 2830 3103 2.01 762 122 <0.001 5.3
33 As arsenic sublimes 616oC/889K 2.18 947 121 0.029 5.8
34 Se selenium 217 490 685 958 2.55 941 117 0.080 4.8
35 Br bromine –7 266 59 332 2.96 1140 114 <0.001 3.1
36 Kr krypton –157 116 –152 121 2.94 1520 109 <0.001 <0.1

The data is plotted below with explanations and comments (Z = proton/atomic number for the x axis)

Above each period graph is the corresponding periodicity graph for the whole of the periodic table

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(1) Variation of 1st Ionisation enthalpy across Period 4

ΔH for the process X(g) ==> X+(g) + e

The energy required to remove the most loosely bound electron (kJmol–1) from the gaseous atoms at 298K/1atm.

You would expect the from potassium to zinc there is a more or less steady rise in the enthalpy of ionisation as the positive nuclear charge increase within the similar quantum energy levels (3d/4s) without increase in shielding from other filled quantum levels. The rise is less so through the 3d block where the 3d/4s quantum levels are close together. However, although the p–block elements generally show a fairly steep rise (as in periods 2 and 3) they are all lowered relative to the previous steady rise presumably due to the shielding effect of the full 3d sub–shell. There is still a small anomaly from arsenic (As) to selenium (Se).

For Period 4, the Group1 Alkali Metal (potassium, lowest Z) has the lowest 1st ionisation energy and the Group 0/18 Noble Gas (krypton, highest Z) has the highest 1st ionisation energy value.

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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(2) Variation of atomic radius across Period 4

There is the general expected decrease in atomic radius from left to right with increasing nuclear charge without quantum level expansion or increase in shielding and so pulling the outer electrons closer. The 3d block of metals (Z = 21 to 30) tend to be similar and in fact tend to go through a small minimum at Mn/Fe.

For Period 3, the Group1 Alkali Metal (potassium, lowest Z) has the largest atomic radius and the Group 7/17 Halogens & Group 0/18 Noble Gas (bromine & krypton, highest Z's) have the smallest atomic radii (there is some uncertainty in the noble gas radii).

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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(3) Variation of electronegativity across Period 4

The expected general increase in electronegativity from left to right is observed but there two minimums at Mn and Zn. Again, the 3d block tend to have similar values.

For Period 4, the Group1 Alkali Metal (potassium, lowest Z) has the lowest electronegativity and the Group 7 Halogen & Group 0/18 Noble Gas (bromine & krypton, highest Z's) have the highest electronegativities (there is some uncertainty in the noble gas electronegativities).

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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(4) Variation of melting points and boiling points across Period 4

At the start of the period 4 you get a steady rise from potassium to vanadium as the number of valency electrons that can contribute to bonding increases. However there is a dip for manganese, a rise to iron and then a steady decline to gallium. The very low values on the right correspond to bromine (Br2 molecules) and krypton (Kr atoms) between which there are only the weakest intermolecular forces.

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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(5) Variation of relative electrical conductivity across Period 4

Copper is quite exceptional in its electrical conductivity. Most other metals are reasonably good conductors and the non–metals bromine and krypton are virtually complete insulators. The rise from potassium to calcium corresponds to 1 ==> 2 delocalised electrons available for conduction. However, their is a drop to scandium after which there is an almost steady rise in conduction presumably correspond to the increase in 3d electrons available for conduction. After that it falls with the 3d electrons no longer available for conduction and the decline in metallic character of the element.

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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(6) Variation of density across Period 4

The density steadily rises to a broad maximum at Co–Ni–Cu. The increase is related to increase in bonding electrons and decreasing radii. After that, the number of electrons contributing to bonding decreases so presumably the atoms are not as tightly bound together and on the right the change from metallic to non–metallic character.

See also 6.3 Period 4 element trends in bonding and  formulae and 6.4 Important element trends down a Group

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WHAT NEXT?

PLEASE NOTE GCSE Level periodic table notes are on separate webpages

Period 2-4 survey sub-index: 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, 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 All 11 Parts have their own sub-indexes near the top of the pages

Group numbering and the modern periodic table

The original group numbers of the periodic table ran from group 1 alkali metals to group 0 noble gases (= group 8). To account for the d block elements and their 'vertical' similarities, in the modern periodic table, groups 3 to group 0/8 are numbered 13 to 18. So, the p block elements are referred to as groups 13 to group 18 at a higher academic level, though the group 3 to 0/8 notation is still used, but usually at a lower academic level. The 3d block elements (Sc to Zn) are now considered the head (top) elements of groups 3 to 12.

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