oxidation numbers
Oxidation numbers can be assigned to different elements in a compound by following a certain set of guidelines.
Encyclopædia Britannica, Inc.
-
© MinutePhysics (A Britannica Publishing Partner)Matter as defined by the Pauli exclusion principle.
-
© MinutePhysics (A Britannica Publishing Partner)Learn about antimatter and its properties.
-
Encyclopædia Britannica, Inc.Molecular compounds are formed when molecules, such as those of methane or water, join together by sharing electrons.
-
University College Cork, Ireland (A Britannica Publishing Partner)Hear a scientist discuss the potential for interdisciplinary research in microbiology, biochemistry, and chemistry.
Transcript
You can assign oxidation numbers to different elements in a compound by following a certain set of guidelines.
Firstly, the oxidation number for all atoms in their elemental state is zero.
That means molecules consisting of atoms of the same elements, such as chlorine gas or nitrogen gas, simply have an oxidation number of zero.
Easy!
Next, the oxidation number of each ion in the ionic compound is equal to the charge on that ion.
In aluminum chloride, made up of aluminum ions and chloride ions, the aluminum ion has an oxidation number of plus three, while the chloride ion has an oxidation number of negative one.
Interestingly, all elements from groups one A, two A, and three A have oxidation numbers corresponding to their group numbers.
So group one A elements have an oxidation number of plus one, group two A of plus two, and group three A of plus 3.
Quite handy!
Oxygen mostly has an oxidation number of minus two. This is true for water and any oxides of group one A, two A or three A elements.
Hydrogen generally has an oxidation number of plus one. This is true for molecules like hydrogen chloride, water, and hydrogen sulfide.
Now, an important rule to remember is that the sum of oxidation numbers of all the elements in a compound must be zero.
This can come in handy if you have to determine the oxidation number of an unknown element. Take aluminum oxide for example.
Start by listing the elements present in the compound: aluminum and oxygen
Next, write the oxidation number of each element: plus three for aluminum; minus two for oxygen.
Then, count the atoms or ions of each element and multiply each oxidation number by that number. So, two ions of aluminum times positive three gives us positive 6...
... while three ions of oxygen times negative two gives us negative 6.
Now, simply add the two numbers together...
..., and you have positive 6 plus negative 6, which equals zero.
Pretty amazing, right?
Firstly, the oxidation number for all atoms in their elemental state is zero.
That means molecules consisting of atoms of the same elements, such as chlorine gas or nitrogen gas, simply have an oxidation number of zero.
Easy!
Next, the oxidation number of each ion in the ionic compound is equal to the charge on that ion.
In aluminum chloride, made up of aluminum ions and chloride ions, the aluminum ion has an oxidation number of plus three, while the chloride ion has an oxidation number of negative one.
Interestingly, all elements from groups one A, two A, and three A have oxidation numbers corresponding to their group numbers.
So group one A elements have an oxidation number of plus one, group two A of plus two, and group three A of plus 3.
Quite handy!
Oxygen mostly has an oxidation number of minus two. This is true for water and any oxides of group one A, two A or three A elements.
Hydrogen generally has an oxidation number of plus one. This is true for molecules like hydrogen chloride, water, and hydrogen sulfide.
Now, an important rule to remember is that the sum of oxidation numbers of all the elements in a compound must be zero.
This can come in handy if you have to determine the oxidation number of an unknown element. Take aluminum oxide for example.
Start by listing the elements present in the compound: aluminum and oxygen
Next, write the oxidation number of each element: plus three for aluminum; minus two for oxygen.
Then, count the atoms or ions of each element and multiply each oxidation number by that number. So, two ions of aluminum times positive three gives us positive 6...
... while three ions of oxygen times negative two gives us negative 6.
Now, simply add the two numbers together...
..., and you have positive 6 plus negative 6, which equals zero.
Pretty amazing, right?