(1) The periodicity of 1st Ionisation enthalpy from elements Z = 1 to 20

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 can be considered to be equal to the number of outer electrons (this is very approximate and NOT a rule) 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.

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

and Survey of Period 3 elements Z = 11 to 18 including the two anomalies.

(2) The periodicity of atomic radius from elements Z = 1 to 20

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, pulling the electron cloud closer to the nucleus without any increase in shielding. The argument is almost identical to that for increasing ionisation energy.

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

and Survey of Period 3 elements Z = 11 to 18.

(3) The periodicity of electronegativity from elements Z = 1 to 20

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.

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

and Survey of Period 3 elements Z = 11 to 18.

(4) The periodicity of melting points and boiling points from elements Z = 1 to 20

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 involved in bonding for the elements of Groups 2 to 4. After this you have simple molecular species only held together by weak intermolecular forces.

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

and Survey of Period 3 elements Z = 11 to 18.

(5) The periodicity of relative electrical conductivity from elements Z = 1 to 20

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 3/13 in Period 3) as the metallic lattice contains 1–2 mobile delocalised electrons involved in electrical conduction. From Group 3 B and from Group 4/14 Si to Group 0/18 the element structure changes to giant covalent lattice or simple molecular structures with no free delocalised electrons within the structure to convey an electric current.

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

and Survey of Period 3 elements Z = 11 to 18.

(6) The periodicity of density from elements Z = 1 to 20

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 Group 1 to Group 3 as the atomic radii decrease and the bonding gets stronger with 1 ==> 3 bonding electrons (delocalised outer valency electrons in the metal lattice). Boron, carbon and silicon have a lower density, typical of non–metallic covalent solids. Nitrogen, oxygen, fluorine, neon, chlorine and argon are small covalent molecules and have very low densities being gaseous at room temperature because only weak intermolecular forces act between them.

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

and Survey of Period 3 elements Z = 11 to 18

WHAT NEXT?

Z = 1 to 38 periodicity plots * Z = 1 to 96 periodicity plots * DATA

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