Molecules, formal charge

Sum of charges on all atoms of a molecule (formal charge of a molecule)... 

The sum of the individual formal charges in a molecule equals ihe overall charge of the molecule formal charges give a sense of where charge is localized within a molecule. 

When several nonequivalent Lewis structures can be drawn for a molecule, formal charge is often used to choose the most appropriate structure(s)... 

Recall that the purpose of Lewis structures is to provide a simple model from which predictions about molecular structure could be made. Sometimes, as we have seen for CO2, there is more than one possible Lewis structure for a molecule. The concept of formal charge has been found useful for determining the best (most useful) Lewis structure for a molecule. Formal charges are assigned to atoms in molecules according to a set of rules. Specifically,... 

Compare and contrast the electrostatic potential map of a typical detergent with that of a typical soap (stearate). Which part of each molecule will be most water soluble (hydrophilic) Draw a Lewis structure that describes each molecule s water-soluble group (make sure you indicate all necessary formal charges and lone pairs). Which part(s) of each molecule will be most grease soluble (lipophilic) What kinds of atoms and bonds are found in these groups ... 

As an illustration, in the iodine monochloride (I — Cl) molecule, the electron pair being shared remains closer to the more electronegative Cl atom. This creates fractional negative and positive charges, referred to as formal charges, on the Cl and I atoms, respectively, as illustrated below ... 

Thomson JOW Click Organic Interactive to learn how to calculate formal charges in organic molecules. 

To express the calculations in a general way, the formal charge on an atom is equal to the number of valence electrons in a neutral, isolated atom minus the number of electrons owned by that atom in a molecule. The number of electrons in the bonded atom, in turn, is equal to half the number of bonding electrons plus the nonbonding, lone-pair electrons. 

Problem 2.8 Calculate formal charges for the nonhvdrogen atoms in the following molecules ... 

Problem 2.9 Organic phosphate groups occur commonly in biological molecules. Calculate formal charges on the four O atoms in the methyl phosphate dianion. 

Plus (+) and minus (-) signs are often used to indicate the presence of formal charges on atoms in molecules. Assigning formal charges to specific atoms is a bookkeeping technique that makes it possible to keep track of the valence electrons around an atom and offers some clues about chemical reactivity. 

Formal charge (Section 2.3) The difference in the number of electrons owned by an atom in a molecule and by the same atom in its elemental state. 

For such odd electron species (sometimes called free radicals) it is impossible to write Lewis structures in which each atom obeys the octet rule. In the NO molecule, the unpaired electron is put on the nitrogen atom, giving both atoms a formal charge of zero ... 

Force The product of mass times acceleration. See also Attractive forces Repulsive forces dipole, 237-238 dispersion, 236,104,107 intermolecular, 227-228,235-236 Formal charge The charge that an atom would have if the bonding electrons in a molecule were equally shared, 171-172,192-193q... 

Lewis structure An electronic structure of a molecule or ion in which electrons are shown by dashes or dots (electron pairs), 166-167,192q formal charge, 171-172 nonmetal oxides, 564-565 oxoacids, 567 resonance forms, 170-171 writing, 168-169 Libby, Willard, 174... 

To assign a formal charge, we establish the ownership of the valence electrons of an atom in a molecule and compare that ownership with the free atom. An atom owns one electron of each bonding pair attached to it and owns its lone pairs completely. The most plausible Lewis structure will be the one in which the formal charges of the atoms are closest to zero. 

Each equivalent atom (the same element, the same number of bonds and lone pairs) has the same formal charge. A check on the calculated formal charges is that their sum is equal to the overall charge of the molecule or ion. For an electrically neutral molecule, the sum of the formal charges is zero. Compare the formal charges of each possible structure. The structure with the lowest formal charges represents the least disturbance of the electronic structures of the atoms and is the most plausible (lowest energy) structure. 

Self-Test 2.8B Suggest a likely structure for the oxygen difluoride molecule. Write its Lewis structure and formal charges. 

Determine the formal charge on each atom in the following molecules. Identify the structure of lower energy in each pair. 

Draw the most important Lewis structure for each of the following ring molecules (which have been drawn without showing the locations of the double bonds). Show all lone pairs and nonzero formal charges. If there are equivalent resonance... 

Quinone, C6H4On is an organic molecule with the structure shown below it can be reduced to the anion C(iI l4Or. (a) Draw the Lewis structure of the reduced product, (b) On the basis of formal charges derived from the Lewis structure, predict which atoms in the molecule are most negatively charged, (c) If two protons are added to the reduced product, where are they most likely to bond ... 

Structural isomers are molecules that have the same formula but in which the atoms are connected in a different order. Two isomers of disulfur difluoride, S2F2, are known. In each the two S atoms are bonded to each other. In one isomer each of the S atoms is bonded to an F atom. In the other isomer, both F atoms are attached to one of the S atoms, (a) In each isomer the S—S bond length is approximately 190 pm. Are the S—S bonds in these isomers single bonds or do they have some double bond character (b) Draw two resonance structures for each isomer, (c) Determine for each isomer which structure is favored by formal charge considerations. Are your conclusions consistent with the S—S bond lengths in the compounds ... 

All atoms in this molecule have a formal charge of zero. 3.103 (a) (b )spid... 

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