[dipesh747]

Hi,

Li - 0.108
Na - 0.218
K - 0.143
Rb - 0.080
Cs - 0.053
Fr - 0.014

Above are the relative electrical conductivities of group 1 alkali metals.

Why does it increase from Li to Na but then go back down.

Well I think it generally goes down because the energy separation between S and P bands  increase as principal quantum number (n) increases.

But I'm not sure what factor overrides this to cause Na to have a significantly higher conductivity than Li.

Any ideas will be helpful!

[Enthalpy]

Conductivity has no direct link with orbital separation. It is linked with the electron's "effective" mass in the solid, which heavy software can compute but is a very indirect result of the crystal form and the underlying orbitals, and in pure metals, with the temperature and allegedly the dispersion relation of phonons, again an indirect consequence of the crystal form and the underlying orbitals.

I'd be extremely surprised if someone could gave a simple relationship with the atomic number.

[dipesh747]

The reason I said it is because Conductivity is proportional to number of charge carriers. In a semi-conductor the number of charge carriers will be related to the number of e- that have enough energy to move into the conduction band (so more charge carriers or a smaller band gap will result in higher conduction).

So is there any particular reason why in group one the conductivity increases then decreases, why does it not decrease down the group ?

Also, what effects the electrons effective mass in a crystal? (all I know about effective mass is that in graphene the electrons effective mass is 0 and they behave as dirac ferimons!)

[Enthalpy]

In a semiconductor, the number of charges is determined by the density of impurities. Exceptions at high temperature or if the gap is very small, and then temperature may suffice to put electrons in the conduction band and holes in the valence band.

No understandable reason for conductivity trends.

Effective mass can't be inferred from simple values like atomic number. It depends on the detailed shape of the bands.

Example: diamond, silicon, germanium have the same valence and crystal shape but different conduction bands, with minimums in the 111 directions for Ge and 110 for Si, resulting from underlying orbitals. Since the effective mass depends on the band's curvature around the minimum, 111 being lower in Ge prevents any comparison with Si, where 110 is lower than 111.

Example: GaAs has the same crystal shape and size as Ge precisely, and the same atomic number as a mean value, but ion charges on Ga and As prevent the minimums in the 111 directions, so the minimum in the conduction band is at 0 for GaAs. Hence no comparison possible with Ge.

Effective mass: it's a relation between the electron's energy E and its moment p=h*k/2pi where k is the number of radians per metre ("wave number") of the electron's wave function. m is defined by E=p²/2m as anywhere. It is a dispersion relation.