The element silicon lies below carbon in Group 14 of the periodic table and is also tetravalent (has four valence electrons). Predict the geometry of a silane molecule, SiH_4 . Silane is a gas that is used in the preparation of extremely pure silicon for semiconductors.
The Lewis formula for a silane molecule is
\begin{matrix}\underset{|}{H} \\ H – Si – H \\ \overset{|}{H} \end{matrix}There are four valence-shell electron pairs (four covalent bonds) about the central silicon atom, so we predict (correctly) that a silane molecule is tetrahedral and that the H–Si–H bond angles are 109.5°.