The chemical formula for Si and H depends on the specific compound you're talking about. Here are some possibilities:

* Silane: The simplest compound of silicon and hydrogen is SiH₄, also known as silane.

* Disilane: Another compound is Si₂H₆, called disilane.

* Trisilane: A compound with three silicon atoms is Si₃H₈, called trisilane.

* Polysilanes: You can have a series of compounds with longer chains of silicon atoms, known as polysilanes. The general formula for a polysilane is SiₙH₂ₙ₊₂.

So, you need to specify the specific compound of silicon and hydrogen you're interested in to get the correct chemical formula.