Question Video: Bonding of the Outermost Electrons in Pure Silicon Physics

Video Transcript

An atom of silicon is part of an object made of silicon atoms, as shown in the diagram. Only the electrons in the outermost shells of the atoms are individually represented. How many of the electrons in the outermost shell of an atom in the object form covalent bonds with adjacent atoms?

Here, we see a lattice of silicon atoms, where the red dots in the center represent silicon nuclei and the blue dots around these red centers represent electrons. The electrons represented in our diagram show only those in the outermost shells of these atoms. Using this representation, a single silicon atom would look like this. There’s the red atomic nucleus, and then there are four valence electrons. When many such atoms are combined to form a lattice, the atoms of silicon form covalent bonds with one another. This involves the sharing of a pair of electrons between a pair of atoms. Through these bonds, it’s possible to effectively fill up the valence shell of a silicon atom.

Since each of the silicon atoms starts out with four valence electrons, having an outermost shell with eight electrons means that four have been added. And these four have been added through shared covalent bonds. We see a demonstration of this with this atom, which is located in the bulk of our silicon lattice. This atom forms a covalent bond with this atom above it, this silicon atom to its right, this silicon atom below it, and this silicon atom to its left. Each one of these four atoms surrounding the central one shares an electron with that central atom. This is how the central silicon atom effectively gains four valence electrons for a complete valence electron shell of eight. In answer to our question then, we can say that four electrons in the outermost shell of an atom in the object form covalent bonds with adjacent atoms.