Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

The weight of a proton and a neutron is approximately the same (1.67 10 -27 kg) whereas the weight of an

electron is only 0.05% of this weight (9.11 10 -31 kg). If an atom lets off or receives electrons it becomes an

ion. An ion is either positively or negatively charged. If an atom lets off one or more electrons the overall

charge will becomes positive and you then have a so-called cation. If an atom receives one or more electrons

the overall charge will be negative and you then have a so-called anion.

When electrons are let off or received the oxidation state of the atom is changed. We will look more into

oxidation states in the following example.

Example 1- B:

Oxidation states for single ions and composite ions

When magnesium and chlorine reacts, the magnesium atom lets of electrons to chlorine and thus the

oxidations states are changed:

2

2

2

2 2 2 : 0 1

2 : 0 2

Mg Cl MgCl

Cl e Cl Oxidationstate forchloride

Mg Mg e Oxidationstate formagnesiumion





 



One sees that the oxidation state equals the charge of the ion. The cations are normally named just by

adding “ion” after the name of the element (Mg+ = magnesium ion) whereas the suffix “-id” replaces the

suffix of the element for anions (Cl- = chloride). For composite ions, a shared (total) oxidation number is

used. This shared oxidation state is the sum of all the oxidation states for the different ions in the

composite ion. Uncharged atoms have the oxidation number of zero. The ammonium ion and hydroxide

are both examples of composite ions:

: 1

4 :^1





OH Oxidation state for hydroxide

NH Oxidation state for ammonium

The oxidation state for hydride is always ”+1” (H+) and the oxidation state for oxide is always “-2” (O2-).

However there are exceptions. For example the oxidation state of oxygen in hydrogen peroxide (H 2 O 2 ) is

“-1” and in lithium hydride (LiH) the oxidation state of hydrogen is “-1”.

Atoms