Oxidation States Flashcards
Oxidation state of a pure element
0 Ex: O2 = 0 H2= 0 Zn=0
Oxidation state of fluorine
-1 whenever it is within a compound.
Oxygen has an oxidation state of -2 unless it is in a compound with Fluorine- in this case oxygen will have a charge of +2
Oxidation state of hydrogen
It can have a value of -1 or +1
When hydrogen is bonded to a non-metal, hydrogen has a charge of +1 and when bonded to a metal, it has a charge of -1.
Oxidation state of carbon
It can vary between -4 and +4.
Oxidation states of SO3
According to the periodic table, both elements would like a charge of -2. However, since oxygen is more electronegative than sulphur, the oxidation state of oxygen will be -2 and we will have to solve the oxidation state for sulphur.
S-> x
O-> 3x (-2)
X -6= 0
X= 6
Oxidation state of oxygen difluoride
Fluorine is more electronegative than oxygen therefore it will have a charge of -1 whereas oxygen will have a charge of +2
2 + (-1x2) = 0
Oxidation state of NO2
Oxygen is more electronegative therefore nitrogen will have a charge of -2 whereas nitrogen will have a positive charge. We can solve it using an equation.
Oxidation states of hydrogen (examples)
CH4- carbon is more electronegative than hydrogen which is why it has a charge of +1
NaH- this is a metal hydride; Hydrogen is more electronegative than sodium which is why it has a charge of -1
H2SO4- sulphate has an oxidation state of -2 since it is more electronegative than hydrogen. This is why it has a charge of +1
Oxidation state of oxygen (peroxide)
When oxygen is in a peroxide, it has a charge of -1
In a peroxide, two oxygen atoms are linked together by a single covalent bond.
Examples:
O2 -2 (-1x2)
Na2O2 - sodium peroxide
H2O2 - hydrogen peroxide
The oxidation state of an ion
The oxidation states of ions made from a single atom equal to its charge. Ex: Na+ -> +1 Mg2+ -> +2 O-2 -> -2
Oxidation states of compounds
Oxidation states of compounds always equal to 0
Ex:
H2SO4- [(1x2)+ (-2)]= 0
( we consider the sulphate ion as one; not each element separately)
CH4- [(-4) + (1x4)]= 0
Polyatomic ions
The oxidation states of each atom in the ion add up to the overall charge of the ion Ex: SO4 -2 Sulphur -> x Oxygen -> -2 x + (4 x -2) = -2 x + (-8) = -2 x = -2 +8 x = +6
Definition of oxidation state
Oxidation states are assigned to atoms in molecules or ions to show how many electrons the atoms has used in bonding.
Electronegativity
The more electronegative species will have the negative value
Electronegativity is the ability of an atom to attract electrons from other atoms.
Electronegativity increases across a period and decreases down a group
Covalent molecules
Covalent molecules are assumed to be ionic
Ex:
H2O- H+ and O2-
The oxidation state of S in S4O6 2-
Sulphur here, has an oxidation state of 2.5
An oxidation state must be a whole number, so this is an average value
Theoretical maximum
The highest possible state for nonmetals is equal to the total number of electrons present the outermost shell of the atom.
Oxidation states of metals
Have positive oxidation states in compounds
The oxidation state is usually that of the Group Number
Where the metal can have multiple oxidation states, this value can never go higher than the Group Number
Mn- +2,+4, +6 and +7
Non-metals
The oxidation states are mostly negative
Can have values that are higher than their Group Number
Naming compounds
Ex: PbO2
We know that the oxidation state of oxygen is -2.
So -2x2= -4
So the oxidation state of Pb should be +4.
So the name of this compound should be Lead (IV) oxide
Ex: Potassium Manganate (VII)
The VII means 7 and this is the oxidation state of manganese in this compound
The ‘ate’ suggests that there is oxygen present in this compound and the oxidation state of this is -2.
The formula for this compound is KMnO4
The total oxidation state of O is -8 (-2x 4)
-8 +1 is -7
Therefore manganese should be +7
