Intermolecular forces and Boiling point

[aminzairi]

Why does disilane, Si2H6 has a higher boiling point than ethane, C2H6

[kw0573]

Neither molecules have permanent dipoles or ability to hydrogen-bond. The difference is that the element silicon has one more shell than carbon, that means silicon is more polarizable. A charge can more readily establish itself on a large atom like silicon, compared to the smaller carbon, where electrons are closer together and repel each other more. Polarizability is also the primary reason why HBr is a much stronger acid than HCl, and by extension than HF. The instantaneous dipoles formed in disilane molecules contribute to greater (London) dispersion forces, which means higher boiling point.