A silicon atom has 14 electrons. In its outmost shell, it has 4 valence electrons.

Covalent bonding in silicon:

Its resistivity drops as temperature rises.

Density of free electrons in silicon can be calculated as:

At T=300K,

 In the same cubic, there are 5×10²² silicon atoms. The ratio of electrons to silicon atoms is tiny tiny…Hence we need to do something to make it conducting.

Most of the information is gathered after watching the youtube video from Prof. Behzad Razavi’s Electronics 1. He is really talented at explaining things. If you have time, just skip mine and watch his video.