Oxidation Number for Ionic Bonds

Oxidation State Practice

Rule 1: For pure elements (unbonded or only bonded with itself), each atom has an oxidation number of zero. 

• The oxidation state of Na in Na is zero (0)

• The oxidation state of H in H₂ is zero (0)

Multiple Choice

What is the oxidation state of S in S₈?

• -2

• -16

• 0

• 2

Rule 2: Monatomic (single) ions have oxidation numbers equal to their charge.

• The oxidation state of Na⁺ is +1

• The oxidation state of S^2- is -2

Rule 3: Oxygen’s oxidation number is -2 except when in peroxides (such as H₂0₂), where it is -1.

• A peroxide is a compound containing 2 +1 cations and 2 oxygen ions

• The oxidation state of O in Na₂O₂ (sodium peroxide) is -1

Multiple Choice

What is the oxidation state of C in CO?

• +4

• -4

• +2

• -2

Rule 4: Hydrogen’s oxidation number is +1, except for when bonded to metals as the hydride ion forming ionic compounds. 

• The oxidation state of H in H₂O is +1

• The oxidation state of H in NaH is -1

Multiple Choice

What is the oxidation state of N in HNO₃?

• +5

• -3

• -1

• -5

Rule 5: Fluorine (F) has an oxidation number of -1 in ALL of its compounds 

• NO EXCEPTIONS!!

Rule 6: Halogens (Cl, Br, I) have negative oxidation numbers when they form halide compounds. When combined with oxygen, they have positive numbers, except for F. 

• The oxidation state of Cl in HCl is -1

• The oxidation state of Cl in HClO₃ is +5

Multiple Choice

What is the oxidation state of Br in HBrO₄?

• -1

• -7

• +7

• -5

Rule 7: In a neutral atom or molecule, the sum of the oxidation numbers must be 0. In a polyatomic ion, the sum of the oxidation numbers of all the atoms in the ion must equal the charge on the ion 

• Use Table E to check charges of polyatomic ions

Multiple Choice

What is the oxidation state of Cr in CrO₄^2- ?

• +6

• +2

• -2

• +8

Multiple Choice

What is the oxidation number of Mn in MnO₄^- ?

• -2

• +2

• +7

• +8

Multiple Choice

What is oxidation number of P in K₃PO₄?

• -2

• -1

• +1

• +5

Multiple Choice

What is oxidation number of K in K₃PO₄?

• -2

• -1

• +1

• +5

Multiple Choice

What is the oxidation number of Cl in FeCl₃?

• -3

• -1

• +1

• +3

Multiple Choice

What is the oxidation number of Fe in FeCl₃?

• -3

• -2

• +2

• +3

Multiple Choice

What is the oxidation state of H in H₂?

• 0

• +1

• -1

• -2

Poll

How are you feeling with oxidation states as of now?

• Really good! 10/10

• Pretty solid, could maybe use some more practice

• Eh, still kinda tricky

• Very confused and need more help here!