A Level Period 4 Elements Survey trends in physical properties GCE AS A2 inorganic revision notes KS5

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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

All my advanced A level inorganic chemistry revision study notes

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 616^oC/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.

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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).

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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).

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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.

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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.

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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.

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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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