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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 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

(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

(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

(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