Oxidation States of Elements to Know for Inorganic Chemistry I

Understanding oxidation states is key in Inorganic Chemistry. They help us track how atoms gain or lose electrons in reactions. By mastering oxidation states, you can better grasp the behavior of elements in various compounds and their roles in redox processes.

1. Definition of oxidation state

   • The oxidation state (or oxidation number) is a measure of the degree of oxidation of an atom in a chemical compound.
   • It represents the hypothetical charge an atom would have if all bonds were ionic.
   • Oxidation states are used to track electron transfer in redox reactions.

2. Rules for assigning oxidation states

   • The oxidation state of an element in its elemental form is always zero (e.g., O2, N2).
   • The oxidation state of a monoatomic ion is equal to its charge (e.g., Na+ has an oxidation state of +1).
   • In compounds, hydrogen typically has an oxidation state of +1, while oxygen usually has -2.

3. Common oxidation states of main group elements

   • Group 1 elements (alkali metals) have an oxidation state of +1.
   • Group 2 elements (alkaline earth metals) typically exhibit an oxidation state of +2.
   • Halogens (Group 17) usually have an oxidation state of -1, but can also be +1, +3, +5, or +7 in compounds.

4. Variable oxidation states of transition metals

   • Transition metals can exhibit multiple oxidation states due to the involvement of d-orbitals in bonding.
   • Common oxidation states include +1, +2, +3, and up to +7 for some elements.
   • The specific oxidation state can influence the color and reactivity of transition metal compounds.

5. Oxidation states in ionic compounds

   • In ionic compounds, the sum of the oxidation states of all ions must equal the overall charge of the compound.
   • Cations (positive ions) have positive oxidation states, while anions (negative ions) have negative oxidation states.
   • Example: In NaCl, Na has an oxidation state of +1 and Cl has -1, resulting in a neutral compound.

6. Oxidation states in covalent compounds

   • In covalent compounds, oxidation states help determine the distribution of electrons between atoms.
   • The more electronegative atom in a bond is assigned a negative oxidation state based on its charge.
   • Example: In H2O, H has an oxidation state of +1 and O has -2.

7. Relationship between oxidation state and electron configuration

   • The oxidation state reflects the number of electrons lost, gained, or shared during chemical bonding.
   • Elements with similar electron configurations often exhibit similar oxidation states.
   • Changes in oxidation state can indicate shifts in electron configuration during reactions.

8. Oxidation states in redox reactions

   • Redox reactions involve the transfer of electrons, leading to changes in oxidation states of the reacting species.
   • Oxidation is the loss of electrons (increase in oxidation state), while reduction is the gain of electrons (decrease in oxidation state).
   • Balancing redox reactions requires ensuring that the total increase in oxidation states equals the total decrease.

9. Disproportionation reactions and oxidation states

   • Disproportionation reactions involve a single substance being simultaneously oxidized and reduced.
   • This results in products with different oxidation states from the original reactant.
   • Example: In the reaction of hydrogen peroxide (H2O2), it can be oxidized to O2 (oxidation state 0) and reduced to water (oxidation state -2).

10. Oxidation states in coordination compounds

    • In coordination compounds, the oxidation state of the central metal ion is determined by the charges of the ligands and the overall charge of the complex.
    • Ligands can be neutral, positively charged, or negatively charged, affecting the oxidation state of the metal.
    • Example: In [Cu(NH3)4]2+, Cu has an oxidation state of +2, while NH3 is a neutral ligand.