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Introduction

Charges, radicals, and lone pairs associated with a chemical structure may be drawn as graphical objects separate from the main structure, or as textual characters within an atom label. The preferred forms vary somewhat according to the circumstances

Charges associated with specific atoms

For the most part, charges should be included within an atom label when possible. The positioning of charges within atom labels is discussed in the section on atom labels and other chemically-significant text. Most commonly, a charge will be associated with a single atom within a structure, and including the charge within the label will rarely pose a problem. The use of floating charges should be avoided except when the charge itself is a noteworthy aspect of the structure

RECOMMENDED	RECOMMENDED	RECOMMENDED	AVOID	AVOID

Charges associated with an atom label that contains a single element symbol plus one or more hydrogen symbols may be included as text within the label or as a separate graphical object. If the charge is represented textually, it should be included in the label after the hydrogen atom(s). If the charge is represented as a separate object, it should be placed adjacent to the symbol of the element that bears the charge in the structure. Separate charge objects may be shown either in circled or uncircled form; the circled form is more visually apparent, and should best be used only in cases where the charge itself is to emphasized. Separate charge objects should preferentially be positioned toward the top-right of the element symbol; however, if there is another element symbol or object already present to the right, the charge may also be positioned above, to the left, or below the atom symbol, whereever there is the most room.

RECOMMENDED	RECOMMENDED	RECOMMENDED

Charges associated with a an atom in the middle of a contracted atom label must be positioned as separate graphical objects. The charge should preferentially be positioned above the element symbol, but may also be positioned below if there is more room there.

RECOMMENDED

Radicals associated with specific atoms

Like charges, localized radicals may be represented as text within atom labels or as separate graphical objects. Unlike charges, however, radicals are most preferentially represented as separate objects. The positioning of radicals within atom labels is discussed in the section on atom labels and other chemically-significant text. If radicals are positioned as separate graphical objects, they should be positioned close to the element with which they are associated. Unlike charges, radicals should preferentially not be positioned toward the top right of the element symbol, but rather exactly above, below, to the left, or to the right of it.

RECOMMENDED

Delocalized charges and radicals

As discussed on the section on aromatic rings and other types of electron delocalization, charges, and radicals that are delocalized across several atoms should always be depicted as separate graphical objects centered within the delocalized system.

RECOMMENDED	AVOID	AVOID	AVOID

Lone pairs

Isolated lone pairs should be positioned, like radicals, close to the element with which they are associated. They should normally be positioned exactly above, below, to the left, or to the right of the atom label, with the two dots of the lone pair parallel to the closest side (horizontally if above or below the label, vertically if to the left or the right). Positioning of lone pairs at other angles should be strongly avoided unless it is impossible to do otherwise.

RECOMMENDED	RECOMMENDED

Lone pairs are also used extensively by the Lewis Convention. Although that convention is very useful for teaching introductory chemistry, its use outside of educational situations is strongly discouraged.

Partial charges

In contrast to formal charges, the partial charge indicators represent unspecified (and usually non-integral) charge values. They are most commonly used as qualitative indicator of electronegativity or electropositivity.

Partial charge indicators may be shown to emphasize the polar nature of certain covalent bonds, to show the charge distribution in a molecule, or to show the atoms participating in hydrogen bonds. The partial charges are designated by symbols δ^- and δ⁺ placed near the atom in question. In neutral molecules that show partial charges, at least one each of the δ^- and δ⁺ symbols must be shown.

RECOMMENDED	RECOMMENDED	RECOMMENDED

The mixing of formal and partial charges in one structure should be avoided. In particular, it is not acceptable to use partial charge indicators to indicate the distribution of a real net charge via resonance.

RECOMMENDED	RECOMMENDED	NOT ACCEPTABLE

Partial charge indicators may also be associated with delocalized systems, just as formal charge indicators may be used.

RECOMMENDED