In MarvinSketch, the charge of an atom is initially set to be neutral.
As bonds or charge (s)are added or removed, MarvinSketch adjusts the number of implicit hydrogens to let the charge remain neutral.
You can set the charge of any atom using
'+' or '-' keys.
The position of the charges can be modify:
Select the charge.
Drag it around the atom.
Optionally, it is possible to display the charge symbols in circles. To set this option, go to the Structure tab of the Preferences dialog located in the Edit menu.