Why is chlorine valued 1

The bonding capacity of the atoms: stoichiometric valence and oxidation number


In order to be able to set up chemical formulas, one must consider the binding capacity of the elements:

The stoichiometric valence of an element indicates how many hydrogen atoms an atom of an element can bind or replace. Hydrogen is monovalent.

The oxidation number also takes into account which charge the atom is thereby - formally by assigning electrons in an electron pair bond or as a specific ion charge.

While the valency represents a kind of element property, an oxidation number can only be given if the atom is actually bound; at most it can be stated in which oxidation states an atom can occur.


A chlorine atom can bond a hydrogen atom. Chlorine is monovalent.

The oxidation number for chlorine is - I, for hydrogen + I

One oxygen atom O can bind two hydrogen atoms H. So oxygen is bivalent. With a few exceptions, an oxygen atom is always bivalent.
The oxidation number of oxygen is - II (for hydrogen again + I
A sodium atom Na can a Replace hydrogen atom, so sodium is monovalent. Sodium is always 1-valued. The oxidation number is + I.


Binding ability













Atomic number





i.e. a divalent atom can bond or replace two monovalent or one divalent atom.

Cl - Mg - Cl orMg = O

a tetravalent atom can bond or replace four monovalent or two divalent atoms:


CCl4 orCO2 corresp. O = C = O

The values ​​for the valencies are as often the opposite as for the atomic number ratios: This results in the "rule of the cross":


The atomic number ratios can of course be shortened, while the valency is an unchangeable material property. Thus, the compound MgO results from the divalent atoms Mg and O, and the carbon dioxide CO results from the tetravalent carbon and the divalent oxygen2

 Values ​​of important elements:

AThe alkali metals (Li, Na, K), the halogens (Cl, Br, J), hydrogen and silver are valuable

TwoMost heavy metals (e.g. Cu, Zn), the alkaline earth metals (Mg, Ca), sulfur S and oxygen O are valuable.

ThreeAluminum Al, some heavy metals (Fe, Cr), nitrogen N and phosphorus P are valuable.

FourCarbon C and silicon Si are valuable.

Many heavy metals and non-metals can also appear in several valencies, e.g. phosphorus (3.5), iron (2.3), lead (2.4), nitrogen (3.5) and sulfur (2.4 and 6).