How does arsenic doping create extra conduction electrons in silicon?

In the process of doping, arsenic is used to modify the electrical properties of silicon by introducing impurities into its crystalline lattice.12

Silicon atoms typically have four electrons in their outer orbit, which they share with four neighboring silicon atoms to form covalent bonds. Arsenic, however, is a pentavalent atom, meaning it possesses five electrons in its outer shell.132

When an arsenic atom replaces a silicon atom in the crystal structure, four of its outer electrons participate in covalent bonding with the surrounding silicon atoms. The fifth electron does not have a bonding partner and is effectively "donated" to the conduction band. Because this extra electron is free to move through the crystal, it increases the material's electrical conductivity. This addition of negative charge carriers classifies the resulting material as an n-type semiconductor, with the arsenic atom acting as a donor.132