Charges
A formal charge is stored on the atom and drawn as a small marker next to its label. Apply it with the Charge tool or a keyboard shortcut, draw it plain or circled, and move the marker by dropdown or by dragging. Charges also change implicit hydrogen counts and are checked by structure validation.
Drawing the acetate ion
- Draw acetic acid: a carbon with a CH₃ carbon, a double-bonded O, and a single-bonded O.
- Click the Charge tool (the +/- icon) and pick the minus preset in the flyout.
- Click the single-bonded oxygen. A minus sign appears beside its label.
With Structure > Display > Show Implicit Hydrogens on, that oxygen now reads O instead of OH, because the negative charge removes the hydrogen from the count. To show the ion’s other resonance form, see Views and resonance.
Adding a charge
Select the Charge tool in the toolbar (the +/- icon). Clicking the button opens a flyout with eight presets: +, -, 2+, 2-, 3+, 3-, and circled plus and minus. Right-clicking the button opens the same flyout without switching to the Charge tool. Pick one, then click an atom to apply it.
Clicking the same atom again with the same charge and style removes the charge, so the tool works as a toggle. Clicking a different preset onto an already-charged atom replaces the value.
Clicking empty canvas creates a standalone charge annotation you can place freely, for example as the net charge outside a bracketed ion.
Keyboard shortcuts
With one or more atoms selected, press + (or =) to increment the charge and - to decrement it. Values are clamped to the range -6 to +6, and the shortcut applies to every selected atom at once. Decrementing through zero removes the marker and clears any per-atom display overrides.
Display styles
Two styles are available: Superscript (plain +, 2-, etc. raised beside the label) and Circle (the symbol inside a circle). The document-wide default lives in the Structure Settings dialog under the Charges tab, along with default size, position, and X/Y offsets. Applying a charge with a style that differs from the document default records a per-atom override; applying one that matches clears the override so the atom follows the global setting again.
Charge Properties panel
Click an existing charge marker with the Charge tool to open the Charge Properties panel (Molkit switches to the Select tool automatically). Its Charge box takes a common value or free text. Typing 2+, 3-, ++, or -- sets both the value and a custom display text, so a doubly charged ion can show ++ instead of 2+. Style switches this charge between Superscript and Circle, Color has a hex field and a reset button, and Size is a multiplier slider from 0.3 to 3 (default 0.85; double-click the slider to reset).
While the panel is open for an atom, pressing Delete removes that charge.
Positioning the marker
By default the marker is placed automatically near the atom label. To override it, select the atom and open the Object Properties panel; the Charge section has a Position dropdown with Auto, Top Right, Top Left, Top Center, Bottom Right, Bottom Left, and Bottom Center.
For exact placement, drag the marker itself. While dragging, alignment guides snap the charge to the edges and center of the atom label. Dragging sets the position to Custom with a stored offset; the marker then moves with the atom.
Effect on chemistry
Charge enters the implicit hydrogen calculation, so a nitrogen with a + charge picks up a fourth hydrogen and a deprotonated oxygen drops one. Structure validation also compares your drawn charge against the computed formal charge and warns when they disagree, which catches missing lone pairs or wrong bond counts. See Validation.
If you draw an ion in brackets with its atoms neutral and a standalone charge outside, validation accepts it as long as that charge equals the sum of the formal charges worked out from the electrons. The net dipole overlay also uses those formal charges to tell whether a molecule is an ion, so a bracketed ion gets no dipole arrow even though no atom carries a charge.