I.E., the stepwise formation constant will decrease with the increase of coordination number.

Oxidation-reduction reactions are electron transfer reactions

The process may involve the complete transfer of electrons to form ionic bonds or only a partial transfer or shift of electrons to form covalent bonds.

Oxidation and reduction occur simultaneously in a chemical reaction; one cannot take place without the other.

Oxidation

is the loss of electrons by a particle in a reaction, resulting in an increase in the oxidation number.

Reduction

is the gain of electrons by a particle in a reaction that results in a decrease in the oxidation number.

Factors affecting the complex equilibrium, Which rules help in assessing oxidation numbers?

Factors affecting the complex equilibrium

Ligands concentrations pH of solutions

Ionic strength of solution

1. Influence of Components or ligands concentration.

If Components or ligands concentrations are high, the complex ions of coordinate number is high.

M^z+ + L = ML^z+

ML^z+ + L = ML₂^z+

ML₂^z+ + L = ML₃^z+

2. Influence of pH

If ligand is salt of strong acid, pH does not influence to complexation

process, b/c ionization of strong acids are completely. The

concentration of hydrogen changes just ionic strength.

If ligand is salt of weak acid, pH influences to ionization of ligands, that

time additional process occurs.

If adding more hydrogen concentration, the equilibrium process is going right side, and influence to destroyed comlpexation.

3. Influence ionic strength of solutions

Change ionic strength to influence ions active coefficient changes, that influence complexation equilibrium process.

Rules that help in assessing oxidation numbers:

– The oxidation number of any free element is zero, even when the atoms are combined with themselves (e.g. O₂, P₄, S₈).

– No regard is paid to covalent bonds between atoms of the same species.

– An element may have more than one oxidation number, if it forms a variety of compounds.

– The oxidation number of hydrogen in a compound or an ion is + I except in ionic hydrides (– I).

– The oxidation number of oxygen in a compound or in an ion is –II except in peroxides (it takes on a – I).

– Metals generally have only positive oxidation numbers in compounds.

– The oxidation number of alkali metals equals always + I,

of alkaline earth metals always + II.

– Nonmetals have negative oxidation numbers when combined with metals, positive oxidation numbers when combined with more electronegative nonmetals.

What is oxidant and reductant? What is the half-reactions and redox pairs?

A quite general reaction:

– n e^–

Ared + Box		Aox + Bred
In this reaction		+ n e–

A_red is oxidize because it loses electrons; it is a reductant (reducing agent) because it acts as donor of electrons and causes another species to be reduced.

B_ox is reduced because it gains electrons; it is an oxidant (oxidizing agent) because it acts as acceptor of electrons and causes another species to be oxidized.

In the reaction

– 2 e^–

Fe(s) + Cu²⁺(aq) Fe²⁺(aq) + Cu(s)

+ 2 e^–

Fe is oxidized, it acts as reductant of Cu²⁺,

Cu²⁺ ion is reduced, it acts as oxidant of Fe.

Every redox reaction can be formally separated into two parts called half-reactions (half-equations, half-cells) that represent either oxidation only or reduction only; they do not occur without the other half-reaction taking place at the same time:

oxidation	Fe	Fe2+	+ 2 e–
reduction	Cu2+	+ 2 e–	Cu

Pairs of the oxidized and reduced species A_ox / A_red and

B_ox / B_red that appear in half-equations are called

redox pairs (or redox couples).

Components of a particular redox pair can differ not only in the number of electrons but also in the number of hydrogen, oxygen, as well as other atoms.

Hydrogenation and dehydrogenation, Oxygenation and deoxygenation. Hydrogenation and hydratation, dehydrogenation and dehydratation are same phenomenon? Why?

Hydrogenation and dehydrogenation are redox reactions, the products of which contain more or less hydrogen atoms

(as well as less or more multiple covalent bonds – the terms saturation or desaturation are also used).

Oxygenation and deoxygenation are redox reactions, the products of which contain more or less oxygen atoms.

A special type of oxygenation is hydroxylation.

Different types of redox reactions – examples:

– Loss and gain of electrons

Zn + Cu2+	Zn2+ + Cu	oxidation of zinc
Cu2+ + Fe	Cu + Fe2+	reduction of cupric ion to copper

– Oxygenation and deoxygenation

C(s) + O₂ →CO₂ oxidation (combustion) of carbon

CO₂→ CO + ½O₂ reduction of carbon dioxide by deoxygenation

– Dehydrogenation and hydrogenation

CH3CH2-OH

– 2H

CH3CH=O dehydrogenation of ethanol to acetaldehyde

→

CH3–C

–COOH

+ 2H

→

CH3–CH–COOH

hydrogenation (reduction)

OH

of pyruvate to lactate

O

Do not confuse the terms

hydrogenation dehydrogenation

and

and

hydratation, dehydratation !

In organic chemistry,

hydrogenated products are sometimes named by adding the prefix dihydro– to the name of a original compound, and dehydrogenated products by adding the prefix dehydro– to the name of a original compound.

Hydratation and dehydratation are not redox reactions; there is no change in the sum of the both carbon oxidation numbers (one of them is oxidized and another is reduced in addition or elimination of water).

Which kind of redox reactions type do you know? What is Standard electrode potentials E⁰, electromotive force (electric driving force)? Nernst equation?

Well-known strong oxidants and reductants – examples:

Oxidizing agents – H₂O₂, KMnO₄, K₂Cr₂O₇, Cl₂, I₂ Reducing agents – H₂, C, Fe, Zn, SnCl₂

Oxidants and reductants differ in their ability to react with other agents considerably.

The strength of oxidants and reductants (their tendency to gain or lose electrons) is expressed for particular redox pairs by standard electrode potentials E⁰.

Standard electrode potential E⁰