Periodicity means the regular occurrence of elements with similar properties giving repeating patterns when selected properties are plotted against proton/atomic number.

(1) The periodicity of 1st ionisation from elements Z = 1 to 38

The peaks correspond with the Noble Gases at the end of a period and the troughs with the Group 1 Alkali Metals at the start of a period.

There is a general increase in 1st ionisation energy from left to right across a period.

As you go across the period from one element to the next, the positive nuclear charge is increasing by one unit as the atomic/proton number increases by one unit and the charge is acting on electrons in the same principal quantum level. The effective nuclear charge is approximately the number of outer electrons and this is increasing from left to right as no new quantum shell is added i.e. no extra shielding. Therefore the outer electron is increasingly more strongly held by the nucleus and so, increasingly, more energy is needed remove it. From elements Z=21 Sc to Z=30 Zn, the increase is relatively gradual as the 3d sub–shell is filled with electrons of similar energy.

For more details see Survey of Period 2 elements Z = 3 to 10

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

(2) The periodicity of atomic radius from elements Z = 1 to 38

The peaks correspond with the Group 1 Alkali Metals at the start of a period and the troughs with the Group 7 Halogens/Group 0 Noble Gases (data uncertain for Group 0) at the end of a period.

There is a general decrease in atomic radius from left to right across a period.

The atomic radius generally decreases from left to right across a period, as the actual and effective nuclear charge increases within the same principal quantum level with increase in proton number, pulls the electron cloud closer to the nucleus without any increase in shielding. The argument is almost identical to that for increasing ionisation energy. in Period 4 from elements Z=21 Sc to Z=30 Zn, the decrease is relatively gradual as the 3d sub–shell is filled with electrons of similar energy and there is actually a small sub–peak for zinc Z=30.

For more details see Survey of Period 2 elements Z = 3 to 10

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

(3) The periodicity of electronegativity from elements Z = 1 to 38

The peaks correspond to the Group 7 Halogens/Group 0 Noble Gases at the end of a period and the troughs' correspond to the most electropositive Group 1 Alkali Metals at the start of a period.

There is a general increase in electronegativity from left to right across a period.

The electronegativity generally increases from left to right across a period, as the actual and effective nuclear charge increases within the same principal quantum level, pulling the electron cloud closer to the nucleus (see 1st IE arguments) i.e. increase in proton charge without increase in shielding. Even in Period 4 the 3d block from Z=21 Sc to Z=30 Zn, they show a steady increase with a small sub–trough for manganese.

For more details see Survey of Period 2 elements Z = 3 to 10,

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

(4) The periodicity of melting points and boiling points from elements Z = 1 to 38

The melting points and boiling points tend to peak in the middle of  Periods 2 and 3 (Groups 3/13 and 4/14) and the lowest values at the end of the period – the Noble Gases. The highest values correspond to giant covalent or metallic lattice structures.

Generally you are moving from a low melting, but still quite high boiling, metallic lattice of the Alkali Metals of moderately strong bonding with one outer delocalised valence electron  ==> a much higher melting and boiling metallic or giant covalent lattice with 2–4 outer electrons for Groups 2 to 4/14 involved in bonding. After this you have simple molecular species only held together by weak intermolecular forces. In Period 4 most of the 3d block have high melting/boiling points due to the extra delocalisation of the 3d electrons to contribute to the metallic bonding, though there is a sub–trough for manganese.

For more details see Survey of Period 2 elements Z = 3 to 10,

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

(5) The periodicity of relative electrical conductivity from elements Z = 1 to 38

The peaks correspond to the metals in the middle of the period with the greatest number of outer electrons that can be delocalised.

The electrical conductivity increases dramatically from left to right for Groups 1–2 (and Al in Group 3 in Period 3) as the metallic lattice contains 1–2–3 mobile delocalised electrons involved in electrical conduction. From Group 4/14 to 0/18 the element structure changes to giant covalent lattice, semi–metal or simple molecular structures with less tendency towards delocalisation or no free delocalised electrons at all, within the structure to convey an electric current. In Period 4 most of the 3d block (₂₁Sc to ₃₀Zn) have fairly high electrical conductivities due to the extra delocalisation of the 3d electrons to contribute to the electrical conduction, and there is a particularly high peak for copper.

For more details see Survey of Period 2 elements Z = 3 to 10,

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

(6) The periodicity of density from elements Z = 1 to 38

The peaks correspond to the metals or non–metals in the middle of the period with the strongest bonding in the solid – giant covalent or metallic lattice structures.

The density increases from lithium to beryllium as the atomic radii decrease and the bonding gets stronger with 1 ==> 2 bonding electrons (delocalised outer valency electrons in the metal lattice). Boron and silicon have a lower density, typical of non–metallic covalent solids. Nitrogen, oxygen, fluorine and neon are small covalent molecules and have very low densities being gaseous at room temperature because only weak intermolecular forces act between them. In Period 4 most of the 3d block (₂₁Sc to ₃₀Zn) fairly high densities due to the extra delocalisation of the 3d electrons contributing to stronger bonding, reduction in atomic radii and hence increasing the density, and the highest peak–highest density corresponds to cobalt, nickel and copper.

For more details see Survey of Period 2 elements Z = 3 to 10,

Survey of Period 3 elements Z = 11 to 18

and Survey of Period 4 elements Z = 19 to 36.

WHAT NEXT?

Z = 1 to 20 periodicity plots * Z = 1 to 96 periodicity plots * DATA