3.1.2 Oxidation Numbers

• What does an oxidation number represent?

  Hypothetical charge of an atom
• An oxidation number represents the hypothetical charge an atom would have if all its bonds were completely ionic
• The oxidation number can only be positive.

  False
• What is the oxidation number of Group 1 elements?

  +1
• Group 1 elements have an oxidation number of +1 in compounds such as NaCl
• Halogens in Group 17 always have an oxidation number of -1.
• What is the usual oxidation number of oxygen in compounds?

  -2
• Match the element group with its common oxidation number:

  Group 1 ↔️ +1

  Group 2 ↔️ +2

  Group 17 (Halogens) ↔️ -1
• Steps for assigning oxidation numbers according to the rules:

  1️⃣ Determine the oxidation number of elements with fixed values (e.g., Group 1, Group 2, Fluorine).

  2️⃣ Assign oxidation numbers to hydrogen and oxygen, considering exceptions.

  3️⃣ Calculate the oxidation numbers of other elements in the compound or ion.

  4️⃣ Ensure the sum of oxidation numbers equals the charge of the compound or ion.
• Neutral compounds have a total oxidation number of 0.
• What is the oxidation number of a monoatomic ion equal to?

  Its charge
• Oxygen usually has an oxidation number of -2, except in peroxides
• What is the oxidation number of hydrogen in metal hydrides?

  -1
• In complex ions, the total oxidation number equals the ion's charge.
• An oxidation number is a hypothetical charge used to determine if an element has been oxidised or reduced
• What is the oxidation number of halogens in compounds with Group 1 elements?

  -1
• In NaCl, sodium has an oxidation number of +1.
• Steps for assigning oxidation numbers using the rules:

  1️⃣ Identify elements in their elemental form and assign them an oxidation number of 0.

  2️⃣ Assign oxidation numbers to monoatomic ions based on their charge.

  3️⃣ Assign oxidation numbers to hydrogen and oxygen, considering exceptions.

  4️⃣ Calculate oxidation numbers of other elements in the compound or ion.

  5️⃣ Ensure the sum of oxidation numbers matches the compound's charge.
• What is the oxidation number of hydrogen in water (H₂O)?

  +1
• Oxygen has an oxidation number of -2 in hydrogen peroxide (H₂O₂).

  False
• The sum of oxidation numbers in a neutral compound is always zero
• What is the oxidation number of fluorine in all its compounds?

  -1
• Elements in their elemental form have an oxidation number of 0.
• Match the element group with its common oxidation number:

  Group 1 ↔️ +1

  Group 2 ↔️ +2

  Halogens ↔️ -1
• What does an oxidation number represent?

  Hypothetical charge of an atom
• An oxidation number is useful for determining if an element has been oxidised or reduced.reduced
• What is the oxidation number of Group 1 elements?

  +1
• The oxidation number of Group 2 elements is +2.+2
• Halogens in Group 17 have an oxidation number of -1 in compounds.
• What is the usual oxidation number of oxygen in compounds?

  -2
• Key rules for assigning oxidation numbers

  1️⃣ Elements in their elemental form have an oxidation number of 0

  2️⃣ Monoatomic ions have an oxidation number equal to their charge

  3️⃣ Hydrogen usually has an oxidation number of +1, except in metal hydrides where it's -1
• What is the oxidation number of an element in its elemental form?

  0
• Monoatomic ions have an oxidation number equal to their charge.
• Hydrogen usually has an oxidation number of +1, except in metal hydrides where it is -1.hydrides
• What is the oxidation number of oxygen in peroxides?

  -1
• The sum of oxidation numbers in a neutral compound is always 0.
• The sum of oxidation numbers in a polyatomic ion equals the ion's charge.charge
• What is the oxidation number of fluorine in its compounds?

  -1
• What are the oxidation numbers of hydrogen and oxygen in water (H₂O)?

  +1 and -2
• During oxidation, an element's oxidation number increases as it loses electrons.increases