BeCl2 and TeCl2 are both covalent molecules, yet BeCl2 is linear while TeCl2 is bent. Explain
The correct answer and explanation is :
The difference in molecular geometry between BeCl₂ (beryllium chloride) and TeCl₂ (tellurium dichloride) can be attributed to the nature of bonding and the electronic configuration of the central atoms in each molecule, specifically focusing on the concept of electron pair repulsion and hybridization.
BeCl₂ (Beryllium Chloride):
Beryllium has an atomic number of 4, so in BeCl₂, the beryllium atom has only two valence electrons. When it forms bonds with two chlorine atoms, it forms two sigma bonds using these electrons. Due to the lack of lone pairs on the beryllium atom and the two bonding pairs of electrons, BeCl₂ adopts a linear geometry. This geometry minimizes electron pair repulsion, as the two bonding pairs of electrons are positioned at 180° from each other, the maximum distance apart in a two-atom system. The absence of lone pairs on the central atom further stabilizes the linear structure.
TeCl₂ (Tellurium Dichloride):
Tellurium, on the other hand, is in Group 16 and has six valence electrons. In TeCl₂, tellurium forms two bonds with chlorine atoms, but it also retains one lone pair of electrons. The lone pair occupies an orbital that is not involved in bonding, and the bonding electron pairs will experience repulsion from the lone pair. According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, lone pairs tend to repel bonding pairs more strongly than bonding pairs repel each other, which leads to a bent geometry. The bonding pairs of electrons, therefore, are pushed closer together, resulting in an angle that is less than 120° (typically around 104.5°), giving TeCl₂ its bent shape.
Summary:
In conclusion, the linear shape of BeCl₂ is due to the absence of lone pairs on the central beryllium atom, allowing the bonding pairs to be arranged at 180°. In contrast, TeCl₂ adopts a bent shape due to the presence of a lone pair on the tellurium atom, which causes the bonding pairs to be pushed together. This demonstrates how lone pairs and bonding pairs affect molecular geometry according to VSEPR theory.