Belisarius already showed how to build a graph with unconnected vertices, and you asked about their positioning.
If you prefer a different arrangement of the unconnected vertices (or the connected components in general), take a look at the
"PackingLayout" suboption of
GraphLayout. The documentation has examples.
Mathematica is smart about graph layouts: it first breaks the graph into connected components, then lays out each component separately, then tries to align each horizontally, finally it packs the components together in a nice way. How exactly it does it is controlled by
Sometimes one might want the result of a dumb layout algorithm that doesn't break the graph into components before performing the layout algorithm. If you want this, take a look at IGraph/M, which will give results similar to this:
Unfortunately most other layout algorithms it provides might get upset when they see disconnected vertices, and place them in unpleasant locations ... but the Furchterman–Reingold (same as
"SpringElectricaEmbedding" in Mathematica) tends to give nice results.