In MarvinSketch, the charge of an atom is initially set to be neutral.
As bonds or charges are added or removed, MarvinSketch adjusts the number of implicit hydrogens to let the charge remain neutral.
You can set the charge of an atom by using one of the following methods:
+ or - keys
The position of the charges can be modified by selecting the charge and dragging it around the atom.
It is also possible to display the charge symbols in circles. To set this option, go to the Structure Tab of the Preferences dialog which can be accessed through the Edit menu.