http://en.wikipedia.org/wiki/Silicon
In its crystalline form, pure silicon has a gray color and a metallic luster. Like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a diamond cubic crystal structure, with a lattice spacing of approximately 0.5430710 nm (5.430710 Å).[7]

The outer electron orbital of silicon, like that of carbon, has four valence electrons. The 1s,2s,2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six.

Pure silicon has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.[8]

Tapi di tabel elementer sebetulnya kalau dilihat per atom, lebih kuat silica atau carbon? Berarti selain itupun masih ada hal lain yang membuat sesuatu keras ya? Mungkin saja selain menarik sebuah atom silica pun melemparkan sebuah atom sehingga sesuatu yang harusnya kuat menjadi tidak kuat jika pasangannya tidak tepat.

Apa sih sebenarnya yang membedakan antara besi dan baja? 

Besi dalam tabel periodik disebut Fe, baja merupakan logam paduan dimana unsur dasarnya Fe (besi) dan C (karbon) sebagai unsur paduan, kandungan unsur karbon dalam baja berkisar 0.2% s/d 2.1%