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.