Write the full electron configuration of Si, Si+4 and Si-4. How many valence electrons are in each of the 3 Si atoms?

In an atom there are levels of energy in the shell and sub shell  

This energy level is expressed in the form of electron configurations.  

Charging electrons in the sub shell uses the following sequence:  

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.  

The electron configuration of the element silicon (Si): 1s² 2s² 2p⁶ 3s² 3p²

valence electrons Si = 4

The electron configuration of the element silicon (Si) +4⇒releases 4 electron: 1s² 2s² 2p⁶

valence electrons Si⁴⁺ = 8

The electron configuration of the element silicon (Si) -4⇒gain 4 electron: 1s² 2s² 2p⁶ 3s² 3p⁶

valence electrons Si⁴⁻ = 8