Atom keyboard shortcut: switch focus between Project tree and Workspace pane?

Option 1: When you are in the Workspace pane (content area), you could do ⌘+SHIFT+\ to switch to the project tree.

And from the Project Tree, if you are on a file, you could just do a right arrow ➝ to switch to the workspace (this actually opens the file if not already opened).

Option 2: You could also use Ctrl+0 to toggle between both views.

EDIT:

Difference between fully loaded state and the italicized title

• The italicized title is the Preview Tab mode. Its like half opening the file to read its contents. It changes to fully loaded when you edit the file. I am not sure of any other user perceived difference asides this.

Difference between Ctrl+0 and ➝ in the context of the workspace

• The former switches to file you had in view in the workspace before switching to the tree, while the latter opens the highlighted file while in the tree (its like actually left/single clicking the file from the tree).

Difference between Ctrl+0 and ⌘+SHIFT+\ in the context of the Project Tree

• The former switches to file you had highlighted in the tree before switching to the workspace while the latter highlights (or selects) the file you are currently viewing in the workspace in the Project tree (sort of like searches for the focussed tab in the Project Tree).

These are my observations, hope it makes sense.