Table 4.3 Rules for Assigning an Oxidation Number (0.N.) General Rules 1. For an atom in its elemental form (Na, O,, Cl,, etc.): O.N. = 0 2. For a monatomic ion: 0.N. = ion charge (with the sign before the numeral) 3. The sum of O.N. values for the atoms in a molecule or formula unit of a compound equals zero. The sum of O.N. values for the atoms in a polyatomic ion equals the ion's charge. Rules for Specific Atoms or Periodic Table Groups 1. For Group 1A(1): 2. For Group 2A(2): 3. For hydrogen: O.N. = +1 in all compounds O.N. = +2 in all compounds O.N. = +1 in combination with nonmetals O.N. = -1 in combination with metals and boron O.N. = -1 in all compounds O.N. = -1 in peroxides O.N. = -2 in all other compounds (except with F) O.N. = -1 in combination with metals, nonmetals (except O), 4. For fluorine: 5. For oxygen: 6. For Group 7A(17): and other halogens lower in the group
Electronic Effects
The effect of electrons that are located in the chemical bonds within the atoms of the molecule is termed an electronic effect. The electronic effect is also explained as the effect through which the reactivity of the compound in one portion is controlled by the electron repulsion or attraction producing in another portion of the molecule.
Drawing Resonance Forms
In organic chemistry, resonance may be a mental exercise that illustrates the delocalization of electrons inside molecules within the valence bond theory of octet bonding. It entails creating several Lewis structures that, when combined, reflect the molecule's entire electronic structure. One Lewis diagram cannot explain the bonding (lone pair, double bond, octet) elaborately. A hybrid describes a combination of possible resonance structures that represents the entire delocalization of electrons within the molecule.
Using Molecular Structure To Predict Equilibrium
Equilibrium does not always imply an equal presence of reactants and products. This signifies that the reaction reaches a point when reactant and product quantities remain constant as the rate of forward and backward reaction is the same. Molecular structures of various compounds can help in predicting equilibrium.
Problem Determine the oxidation number (O.N.) of each element in these species: (a) Zinc chloride (b) Sulfur trioxide (c) Nitric acid (d) Dichromate ion
Plan We determine the formulas and consult as shown, including the general rules that the O.N. values for a compound add up to zero and those for a polyatomic ion add up to the ion’s charge.
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