11/21/2023 0 Comments Formail charge of carbonIn the second structure, the two oxygen atoms have the bonding patterns –O= and –O. However, the structures are not equivalent. In the first structure, the two oxygen atoms have the bonding patterns –O– and =O. For example, consider the following two structures for nitrous acid, HNO 2.īoth of these structures obey the rules for drawing Lewis structures they have the correct number of electrons, and all atoms (other than H) obey the octet rule. In addition, we have not moved any atoms around both structures have the arrangement H–O–N–O. Sometimes, it’s possible to draw two legitimate Lewis structures for the same arrangement of atoms without the structures being equivalent. What if resonance structures are not equivalent? In general, all legitimate resonance structures for a given molecule will have the same number of double bonds.įinally, the structure below is also incorrect, but for yet another reason: chlorine is in group 7A, and the group 7A elements cannot form double bonds. It obeys the octet rule, but HCO 2 – must have a total of 18 electrons, and the structure below has 20. The structure below is also incorrect, but for a different reason. In the example below (the chloroformate ion, ClCO 2 –), the first two structures are legitimate, but the third and fourth structures violate the octet rule (the central atom has only six electrons in structure #3, and it has ten electrons in structure #4). However, the two structures below are legitimate resonance structures, and we would need to average them to find the true structure of bicarbonate ion.ģ) Resonance structures cannot disobey the octet rule. The true structure of HCO 3 – is not the average of these two structures. Never move atoms.įor example, the following two structures are not legitimate resonance structures, because we have moved the hydrogen atom. Ozone never looks like this either: O-O=OĢ) In resonance, you can only move electrons. Ozone does not go back and forth between the two structures we can draw. It never has one short bond and one long bond. There are three common misunderstandings about resonance theory. Be careful not to fall into these traps!ġ) Resonance does not mean that the molecule goes back and forth between the structures. Resonance structures are particularly common in oxoanions of the p-block elements, such as sulfate and phosphate, and in aromatic hydrocarbons, such as benzene and naphthalene. If we place a single bonding electron pair between each pair of carbon atoms and between each carbon and a hydrogen atom, we obtain the following: Draw the resonance structures for benzene.Ī Each hydrogen atom contributes 1 valence electron, and each carbon atom contributes 4 valence electrons, for a total of (6 × 1) + (6 × 4) = 30 valence electrons.Subtract this number from the total number of valence electrons in benzene and then locate the remaining electrons such that each atom in the structure reaches an octet.Then calculate the number of valence electrons used in this drawing. Draw a structure for benzene illustrating the bonded atoms.Given: molecular formula and molecular geometry Use resonance structures to describe the bonding in benzene. \)) consists of a regular hexagon of carbon atoms, each of which is also bonded to a hydrogen atom.
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