" Furthermore, because silicon packs on more protons than carbon, it's bulkier, like carbon with fifty extra pounds. Sometimes that's not a big deal. Silicon might substitute adequately for carbon in the Martian equivalent of fats or proteins. But carbon also contorts itself into ringed molecules we call sugars. Rings are states of high-tension- which means they store lots of energy-and silicon just isn't supple enough to bend into the right position to form rings. In a related problem, silicon atoms cannot squeeze their electrons into tight spaces for double bonds, which appear in virtually every complicated biochemical. "

― Sam Kean , The Disappearing Spoon: And Other True Tales of Madness, Love, and the History of the World from the Periodic Table of the Elements