Chemical Bonding | Ionic bonding | Covalent bonding

Ionic bonding:In ionic bonding, electrons are completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond.

Covalent bonding:The second major type of atomic bonding occurs when atoms share electrons. As opposed to ionic bonding in which a complete transfer of electrons occurs, covalent bonding occurs when two (or more) elements share electrons. Covalent bonding occurs because the atoms in the compound have a similar tendency for electrons (generally to gain electrons). This most commonly occurs when two nonmetals bond together.

Multiple Bonds: For every pair of electrons shared between two atoms, a single covalent bond is formed. Some atoms can share multiple pairs of electrons, forming multiple covalent bonds. For example, oxygen (which has six valence electrons) needs two electrons to complete its valence shell.

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Chemical kinetics

Chemical kinetics

The rate of a chemical reaction is a measure of how the concentration or pressure of the involved substances changes with time. Analysis of reaction rates is important for several applications, such as in chemical engineering or in chemical equilibrium study.

Rates of reaction depends basically on:

Reactant concentrations, which usually make the reaction happen at a faster rate if raised through increased collisions per unit time,

Surface area available for contact between the reactants, in particular solid ones in heterogeneous systems. Larger surface area leads to higher reaction rates.

Pressure, by increasing the pressure, you decrease the volume between molecules. This will increase the frequency of collisions of molecules.

Activation energy, which is defined as the amount of energy required to make the reaction start and carry on spontaneously. Higher activation energy implies that the reactants need more energy to start than a reaction with a lower activation energy.

Temperature, which hastens reactions if raised, since higher temperature increases the energy of the molecules, creating more collisions per unit time,

The presence or absence of a catalyst. Catalysts are substances which change the pathway (mechanism) of a reaction which in turn increases the speed of a reaction by lowering the activation energy needed for the reaction to take place. A catalyst is not destroyed or changed during a reaction, so it can be used again.

For some reactions, the presence of electromagnetic radiation, most notably ultraviolet, is needed to promote the breaking of bonds to start the reaction. This is particularly true for reactions involving radicals.

Reaction rates are related to the concentrations of substances involved in reactions, as quantified by the rate law of each reaction. Note that some reactions have rates that are independent of reactant concentrations. These are called zero order reactions.

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Organic reactions

Organic reactions encompass a wide assortment of reactions involving compounds which have carbon as the main element in their molecular structure. The reactions in which an organic compound may take part are largely defined by its functional groups.

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Disproportionation

Disproportionation a redox reaction in which one reactant forming two distinct products varying in oxidation state.

2 Sn2+(aq) → Sn(s) + Sn4+(aq)

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Combustion

Combustion: a kind of redox reaction in which any combustible substance combines with an oxidizing element, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used for only large-scale oxidation of whole molecules, i.e. a controlled oxidation of a single functional group is not combustion.

C₁₀H₈+ 12 O₂ → 10 CO₂ + 4 H₂O

CH₂S + 6 F₂ → CF₄ + 2 HF + SF₆

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Redox reactions

Redox reactions: in which changes in oxidation numbers of atoms in involved species occur.

Those reactions can often be interpreted as transferences of electrons between different molecular sites or species.

An example of a redox reaction is:

2 S₂O₃²⁻_(aq) + I_2(aq) → S₄O₆²⁻_(aq) + 2 I⁻_(aq)

In which I₂ is reduced to I^- and S₂O₃^2- (thiosulfate anion) is oxidized to S₄O₆^2-.

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Acid-base reaction

Acid-base reactions: broadly characterized as reactions between an acid and a base, can have different definitions depending on the acid-base concept employed.

Some of the most common are:

Arrhenius definition: Acids dissociate in water releasing H3O+ ions; bases dissociate in water releasing OH- ions.

Bronsted-Lowry definition: Acids are proton (H+) donors; bases are proton acceptors. Includes the Arrhenius definition.

Lewis definition: Acids are electron-pair acceptors; bases are electron-pair donors. Includes the Brønsted-Lowry definition.

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Metathesis or Double displacement reaction

Metathesis or double displacement reaction:

in which two compounds exchange ions or bonds to form different compounds

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

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Single displacement or substitution

Single displacement or substitution:

characterized by an element being displaced out of a compound by a more reactive element:
2 Na(s) + 2 HCl(aq) → 2 NaCl(aq) + H2(g)

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Direct combination or synthesis

Direct combination or synthesis: in which 2 or more chemical elements or compounds unite to form a more complex product: N2 + 3 H2 → 2 NH3

A chemical synthesis begins by selection of compounds that are known as reagents or reactants. Various reaction types can be applied to these to synthesize the product, or an intermediate product. This requires mixing the compounds in a reaction vessel such as a chemical reactor or a simple round-bottom flask. Many reactions require some form of work-up procedure before the final product is isolated.

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Isomerisation

Isomerisation: in which a chemical compound undergoes a structural rearrangement without any change in its net atomic composition.

Isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C → B-A-C (these related molecules are known as isomers).

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Examples of exothermic reactions

An exothermic reaction is a chemical reaction that releases energy in the form of heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:

reactants → products + energy

Examples of exothermic reactions

• Combustion reactions of fuels
• Neutralization reactions such as direct reaction of acid and base
• Adding concentrated acid to water
• Burning of a substance
• Adding water to anhydrous copper(II) sulfate
• The thermite reaction
• Reactions taking place in a self-heating can based on lime and aluminum
• The setting of cement and concrete
• Many corrosion reactions such as oxidation of metals
• Most polymerisation reactions
• The Haber-Bosch process of ammonia production

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