Oxidation numbers Flashcards
What are the oxidation number rules?
A set of rules to work is a redox is taking place and if so, which element is reduced and oxidised
What is the most important oxidation rule?
Oxidation refers to an individual atom and are mostly always the same element and they are written with the +/- sign before the number
What is oxidation number significance in covalent compounds?
It has no significance in covalent compounds (any compound with covalent bonding)
What is the first oxidation number rule?
Atoms of uncombined always have an oxidation number of 0
What is the second oxidation number rule?
Group 1 element atoms have an oxidation number of +1
What is the third oxidation number rule?
Group 2 element atoms have an oxidation number of +2
What is the fourth oxidation number rule?
Fluorine atoms have an oxidation number of -1
What is the fifth oxidation number rule?
Oxygen atoms have an oxidation number of -2 except when in a peroxide (e.g, H2O2 - hydrogen peroxide) then it is -1
What is the sixth oxidation number rule?
Hydrogen atoms have an oxidation number of +1 except when in a metal hydride (which is only metal & hydrogen , e.g, LiH) then it is -1
What is the oxidation number rule about simple ions?
The sum of the oxidation numbers equals the charge on the ion, e.g, I- = -1
What is the oxidation number rule about compound ions?
The oxidation numbers must all add up to the charge of the ion (in polyatomic ions), e.g, SO4 2- = -2
What is the oxidation number rule about neutral compounds?
The sum of oxidation numbers is 0 (but must account for formula in compounds)
What do roman numerals indicate?
The oxidation number of the element and they are always positive
What do roman numerals after a metal indicate?
The oxidation number of the metal (but are only used when the metal can form more than one ion e.g, Fe(III) = Fe 3+
What do roman numerals written after a compound ion indicate?
The oxidation number of the element in the ion which is not oxygen
What is oxidation (in terms of oxidation number)?
Increase in oxidation number
What is reduction (in terms of oxidation number)?
Decrease in oxidation number
How do you work out which element has been oxidised and reduced using oxidation numbers?
First, assign oxidation numbers to everything in the equation (no balancing) and then identify the increase (oxidation) and decrease (reduction)
How do you describe that an element has been oxidised?
(The element) has been oxidised because it’s oxidation number has increased from (X) to (Y)
How do you describe if an element has been reduced?
(The element) has been reduced because it’s oxidation number has decreased from (X) to (Y)
