Sulfides silicon-phosphorus bonds

The main difference from C, N, and O is that Si, P, and S can form more bonds than the first row elements. This is because they have more orbitals the five 3d orbitals added to the 3s and three 3p orbitals. Silicon forms tetrahedral silanes, rather like alkanes, but also forms stable five-valent anions. Phosphorus forms phosphines, rather like amines, but also tetrahedral phosphine oxides. Sulfur can have any coordination number horn zero to seven, forming sulfides, like ethers, and tetrahedral sulfones with six bonds to sulfur. And it is with sulfur that we start. 

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