Why does gallium have less MP &BP than aluminium?

Question

gallium has slightly less atomic size as compared to aluminium as it has 10 electrons in 3d orbital which have less penetration power,even then why does it has less MP & BP than aluminium

Answer 1

In fact Gallium has slightly bigger atomic size than aluminium.Its atomic radius is 130picometer against 125 of aluminium.

The melting point temperature of 30°C allows the metal to be melted in one's hand. This metal has a strong tendency to supercool below its melting point/freezing point, thus necessitating seeding in order to solidify. Gallium is one of the metals (with caesium, rubidium, francium and mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometers. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low vapor pressure at high temperatures. Unlike mercury, liquid gallium metal wets glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions). For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers.

Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell. Each atom has only one nearest neighbor (at a distance of 244 pm) and six other neighbors within additional 39 pm. Many stable and metastable phases are found as function of temperature and pressure.



The bonding between the nearest neighbors is found to be of covalent character, hence Ga2 dimers are seen as the fundamental building blocks of the crystal. The compound with arsenic, gallium arsenide is a semiconductor commonly used in light-emitting diodes.

Aluminium atoms are arranged in an FCC structure. Aluminium has a high stacking-fault energy of approximately 200 mJ/m².[3]

Answer 2

Actually, gallium atoms are somewhat LARGER than aluminum atoms 136 pm vs 118 pm. Maybe that will help to clarify the problem. Larger atomic size leads to less dense packing of atoms and lower attractions.

Answer 3

the orthorhombic crystal structure of gallium makes the gallium atom to have only one nearest neighbor and so it behaves similar to a p-block diatomic molecule which have characteristic low melting and boiling points. That is the gallium solid phase behaves as if it were composed of discrete molecules of Ga2 molecules.