Silicon forms four bonds with four oxygens because it is larger than carbon and oxygen so the silicon 3p orbital and the oxygen 2p overlap will not be as favorable as the carbon 2p orbital and oxygen 2p overlap.

Carbon forms four bonds with four oxygens because carbon is smaller than silicon so the carbon 2p orbital and the oxygen 2p overlap will be more favorable.

Silicon forms two double bonds with two oxygens because silicon is larger than carbon and oxygen so the silicon 3p orbital and the oxygen 2p overlap will be favored forming two double bonds with oxygen.

Carbon forms two double bonds with two oxygens because carbon is smaller than silicon so the carbon 2p orbital and the oxygen 2p overlap will not be as favorable as the silicon 3p orbital and the oxygen 2p overlap.