Oxidation Numbers of Elements in Periodic Table | s,p,d blocks

Some elements in the periodic table have only one oxidation number or two oxidation numbers. But some have lot of oxidation numbers. Oxidation number of element in a compound can be positive or negative or may be zero.

In sodium compounds, sodium only forms +1 oxidation number.

But some types of atoms such as chlorine form various oxidation numbers like -1, 0, +1, +3, +5, +7 oxidation numbers in compounds.


In this tutorial, we discuss about some important facts of oxidation states and oxidation numbers in periodoc table including s block, p block and d block.


Important facts of oxidation numbers

In this chapter, we discuss very important facts about oxidation numbers.


Oxidation number can be positive or negative

  • We know metals release electrons to form positive ions. Therefore metals always form positive oxidation numbers.
  • But non metals such as sulfur, phosphorus, chlorine can show both positive or negative oxidation numbers.

More than one oxidation numbers of a element

Some elements can show more than one oxidation states. Specially d block elements show this behavior.

Examples to more than one oxidation numbers of a element

  • Chlorine : -1 , 0 , +1 , +3 , +5 , +7
  • Manganese : 0 , +2 , +4 , +7

When an element has not combined or do not form a compound

When an element has not combined, it's oxidation number becomes 0.

Ex: oxidation number of Au is 0.


When an element has combined with same kind element.

When an element has combined with same kind element, it's oxidation number becomes 0.

Ex: oxidation number of Br in Br2 is 0.


Oxidation states of s block

  • All alkali metals show only 0 and +1 oxidation state.
  • All alkali earth metals show only 0 and +2 oxidation states.

Usually, alkali metals and alkali earth metals exits as compounds(NaCl, CaCO3). Therefore we can't see them as free elements.


Oxidation states of p block elements

Some p block elements have lot of oxidation numbers such as chlorine(-1, 0, +1, +3, +5, +7) and sulfur(-2, 0, +4, +6).



Periodic table with oxidation numbers

Here we are going to summarize oxidation numbers of all elements in the periodic table into one group.

NOTE: * is for rare oxidation number

Atomic Number Element Oxidation numbers
1 Hydrogen -1 , 0 , +1
2 Helium 0
3 Lithium +1
4 Beryllium +2
5 Boron +3
6 Carbon -4 , -3 , -2 , -1 , 0 , +1 , +2 , +3 , +4
7 Nitrogen -5 , -4 , -3 , -2 , -1 , 0 , +1 , +2 , +3
8 Oxygen -2 , -1 , 0 , +1 , +2
9 Fluorine -1 , 0
10 Neon 0
11 Sodium +1
12 Magnesium +2
13 Aluminium +3
14 Silicon 0 , +4
15 Phosphorous 0 , +1 , +3 , +5
16 Sulfur -2 , 0 , +2 , +4 , +6
17 Chlorine -1 , 0 , +1 , +3 , +5 , +7
18 Argon 0
19 Potassium +1
20 Calcium +2


s Block

Oxidation numbers of group 1 group 2 elements are studied.



Hydrogen

Hydrogen forms three oxidation states, -1 , 0 , +1. Oxidation number 0 occurs only in hydrogen molecule.

-1 oxidation state - Examples

When hydrogen forms compounds with metals, hydrogen's oxidation number is -1. NaH and CaH2 are some examples.


+1 oxidation number

When carbon form compounds with non-metal elements, oxidation number of hydrogen become +1 in most occasions.

  • Methane: CH4 - Electronegativity of carbon is higher than hydrogen. So hydrogen is oxidized and oxidation number is +1.


Alkali Metals - Group 1

Alkali metals (except hydrogen) remove one electron to form +1 ion. So only oxidation number of alkali metals is +1. So Lithium, Sodium, Potassium, Rubidium, Cesium have only single oxidation number is +1.



Alkali Earth Metals - Group 2

As alkali metals, alkali earth metals only form +2 oxidation state. Beryllium, Magnesium, Calcium, Strontium, Barium have +2 oxidation number.



p Block



Group 3

Group three elements are Boron, Aluminium, Galleum, Indium and Thallium.


Boron

  • +3: BCl3 , BF3

Aluminium (Aluminum)

Aluminium is a metal. So it removes its three electrons of the last shell to show +3 oxidation number. Some examples for +3 oxidation states of aluminium are AlCl3, Al2O3.



Group 4


Carbon

Oxidation numbers of carbon changes from -4 to +4.

  • -4: CH4 - Methane
  • -3: CH3CH3 - Ethane
  • -2: CH3Cl
  • -1: ClCH2CH2Cl
  • 0 : CH2Cl2
  • +1: CH3-CHO - Carbonyl carbon has the +1 oxidation state.
  • +2: CHCl3
  • +3: CH3-COOH - Carboxylic acid carbon atom has the +3 oxidation number.
  • +4: CCl4 , CO2


Group 5

Group 5 includes Nitrogen, Phosphorous, Arsenic, Antimony and Bismuth. Oxidation number variation change when going down the group.


Nitrogen

Nitrogen has various oxidation numbers from -3 to +5.



Phosphorous

Phosphorous also have various oxidation numbers from -3 to +5.

  • -3: Na3P, Ca3P2, PH3
  • -0: P8 , P4
  • -+1: H3PO2
  • +3: P2O3 , H3PO3
  • +5: H3PO4 , Na3PO4 , P2O5


Group 6

We are going to discuss about oxidation numbers of oxygen and sulfur under group 6 elements.


Oxygen

Oxygen has the second highest electronegative value in periodic table. So in most occasions, oxidation number of oxygen is negative. Oxygen only forms positive oxidation numbers when it combine with fluorine.

  • +2: In F2
  • 0: Oxygen molecule (O2)
  • -1: Example for -1 oxidation state is hydrogen peroxide (H2O2).
  • -2: Most common oxidation number of oxygen is -2. Na2O, MgO, H2O are examples to -2 oxidation state of oxygen.


Sulfur

Sulfur is another p block element which has different oxidation numbers.

  • -2: Na2S , H2S
  • 0: S8
  • +4: SO2 , H2SO3
  • +6: H2SO4 , BaSO4


Chlorine

Chlorine also have lot of oxidation numbers. (from -1 to +7)


  • -1: HCl , NaCl
  • 0: Cl2 gas
  • +1 : HOCl , NaClO
  • +3: NaClO2
  • +5: NaClO3
  • +7: NaClO4 , HClO4


3d metals

Most of the 3d metals have variable oxidation numbers. As an example, iron have two oxidation numbers, +2 and +3.

  • +2: FeO, FeCl2
  • +3: Fe2O3

Zinc only has one oxidation number, +2.



3d metals variable oxidation states

3d Metal Oxidation state
Sc +3
Ti +2 , +3 ,+4
Va +2 , +3 , +4 , +5
Cr +2 , +3 , +6
Mn +2 , +4 , +6 , +7
Fe +2 , +3
Co 2 , +3
Ni +2
Cu +1 , +2
Zn +2

Oxidation number and colour of compound or solution

Let's take an example.

  • FeCl2 - green
  • FeCl3 - brown


Why chlorine has wide range of oxidation states than sulfur?

Sulfur and chlorine and are positioned at 6th and 7th groups of the periodic table. So there are six and seven electrons at their final energy levels respectively. These electrons can be combined with oxygen to form different compounds. Some examples are discussed below.

Sulfur gives its all last six electrons to make sulfuric acid molecule (+6 oxidation state). Chlorine can give seven electrons to make chloric acid to show +7 oxidation number.

Chlorine can take one electron to form chloride anion.(-1 oxidation state). Sulfur can take two electrons to form sulfide anion. (-2 oxidation state).


Common oxidation states of sulfur


Common Oxidation State Example Compound
-2 H2S
0 Elemental sulfur (S8)
+4 SO2
+6 SO3 , H2SO4


Common oxidation states of chlorine


Common Oxidation State Example Compound
-1 HCl
0 Cl2
+1 HOCl
+3 HClO2
+5 HClO3
+7 HClO4

Oxidation number of chlorine in Ca(OCl)2

Charge of hypochlorite ion OCl- is -1. So we can calculate oxidation number of chlorine.

-2 + x = -1

x = +1

oxidation number of chlorine in Ca(OCl)2 is +1.



Do not confuse with oxidation number and charge of ion

Oxidation number and charge of ion is not equal at every time.

  • Na+ ion's oxidation number (+1) and charge of ion(+1) are same.
  • Cl- ion oxidation number and charge of ion are same.
  • But in KMnO4, oxidation number of manganese atom is +7. But manganese did not form a +7 ion in KMnO4.
  • Chromium does not form +6 ion. But in K2CrO4, oxidation number of chromium is +6.


What are the elements which have highest oxidation numbers in periodic table?

As a metal, manganese have +7 oxidation number. Some example compounds for +7 are Potassium permanganate ( KMnO4 ), Mn2O7

As a non-metal, chlorine forms +7 oxidation number. HClO4, Cl2O7 are examples for +7 oxidation number of chlorine.



Which element has the zero or positive oxidation number always?

Fluorine has the zero or positive oxidation number always because fluorine is the most electronegative element in the periodic table. So it always gains an electron when fluorine combines with different element to form -1 oxidation number. Fluorine form zero oxidation number in F2 molecule.

In NaF and HF, oxidation number of fluorine is -1.



Give an example reaction to chlorine become positive oxidation number after a reaction?

Chlorine gas (oxidation number 0) reacts with cold dilute NaOH or hot concentrated NaOH to give +1 and +5 oxidation states of chlorine atom respectively.

  • +1: NaClO
  • +5: NaClO3


In p block elements, what is the maximum oxidation number?

Group VII elements form highest oxidation numbers. From group VII, chlorine form +7 oxidation number.



Which elements have the +7 oxidation number and give examples?

Both manganese and chlorine have +7 oxidation number. In potassium permanganate ( KMnO4) and HMnO4, manganese oxidation number is +7. Chlorine forms chloric acid (HClO4) to show +7 oxidation number.



Oxidation state and acidity

When oxidation number increases, acidity strength also increases. Consider acidity of different oxides of nitrogen.

N2O and NO are neutral acidic gases and other oxides of nitrogen ( N2O3, NO2, N2O4 and N2O5 ) are acidic. N2O5 is a strong acidic compound.



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