Chemical Bonding | Ionic bonding | Covalent bonding

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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.

Chemical kinetics

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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.

Organic reactions

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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.

Disproportionation

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Disproportionation a redox reaction in which one reactant forming two distinct products varying in oxidation state.
2 Sn2+(aq) → Sn(s) + Sn4+(aq)

Combustion

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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

Redox reactions

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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) + I2(aq) → S4O62−(aq) + 2 I(aq)
In which I2 is reduced to I- and S2O32- (thiosulfate anion) is oxidized to S4O62-.

Acid-base reaction

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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.

Metathesis or Double displacement reaction

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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)

Single displacement or substitution

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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)

Direct combination or synthesis

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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.

Isomerisation

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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).

Formation_of_decaphenylferrocene_linkage_isomer

Examples of exothermic reactions

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exothermic-reaction
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

Sodium Cyanide: A fatal substance.

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It is a highly toxic compound, also known as sodium salt of hydrodyamic and cyanogran.


Immediate medical attention is required in the event of cyanide poisoning, as it is quickly fatal.


It is used in extracting gold, silver, copper, poison to control indoor pests.


It irritates and severely damages tissues of eyes, skin, respiratory tract and the gastroinstestial tract.


Inhalation causes headaches, dizziness, convulsion, vomiting, unconsciousness, redness of eyes and skin, severe deep burns and nausea.

Talc: Talcum powders are potential carcinogens.

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It is used as cosmetic talcum powder and baby powder.


It is an astringent powder used to preventing rashes on the area covered by a diaper (diaper rash) , food additive or in pharmaceutical products.


Several studies have established preliminary links between talc and pulmonary issues, lung, skin and ovarian cancer and tumours in animals.

Polyquaternium: An allergan in Moisturizing lotions.

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It is used in a variety of cosmetics such as hair care and moisturizing lotions.


It creates allergic contact dermatitis.

Polysorbate-n (20-85): A skin irritant in Suntan Lotions.

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It is used as an emulsifier in cosmetic creams, lotions, cream deodorant, baby oil and suntan lotion.

It can cause contact sensitivity and skin irritation

Petroleum distillates: A potential carcinogen

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It is extremely hazardous for humans.


It may cause cancer and lung damage if swallowed.


Many chemicals are petroleum based, for example 95% of all synthetic fragrances creating serious health problems.

Teff: An alternative grain for Wheat

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Teff is an intriguing grain, ancient, minute in size, and packed with nutrition. Teff is believed to have originated in Ethiopia between 4000 and 1000 BC. Teff seeds were discovered in a pyramid thought to date back to 3359 BC.


The grain has been widely cultivated and used in the countries of Ethiopia, India and it's colonies, and Australia. Teff is grown primarily as a cereal crop in Ethiopia where it is ground into flour, fermented for three days then made into enjera, a sourdough type flat bread. It is also eaten as porridge and used as an ingredient of home-brewed alcoholic drinks. The grass is grown as forage for cattle and is also used as a component in adobe construction in Ethiopia. At this time it is not widely known or used in the U.S., though it is cultivated in South Dakota and Idaho and is available in many health food stores.


The word teff is thought to have been derived from the Amharic word teffa which means "lost," due to small size of the grain and how easily it is lost if dropped. It is the smallest grain in the world, measuring only about 1/32 of an inch in diameter and taking 150 grains to weigh as much as one grain of wheat. The common English names for teff are teff, lovegrass, and annual bunch grass.


Because the grains of teff are so small, the bulk of the grain consists of the bran and germ. This makes teff nutrient dense as the bran and germ are the most nutritious parts of any grain. This grain has a very high calcium content, and contains high levels of phosphorous, iron, copper, aluminum, barium, and thiamin. It is considered to have an excellent amino acid composition, with lysine levels higher than wheat or barley. Teff is high in protein, carbohydrates, and fiber. It contains no gluten so it is appropriate for those with gluten intolerance.


The color of the Teff grains can be ivory, light tan to deep brown or dark reddish brown purple, depending on the variety. Teff has a mild, nutty, and a slight molasses like sweetness. The white teff has a chestnut-like flavor and the darker varieties are earthier and taste more like hazelnuts. The grain is somewhat mucilaginous. It is interesting that documents dated in the late 1800's indicate the upper class consumed the lighter grains, the dark grain was the food of soldiers and servants, and cattle consumed hay made from teff.


Teff is a fine stemmed, tufted annual grass characterized by a large crown, many shoots, and a shallow diverse root system. The plants germinate quickly and are adapted to environments ranging from drought stress to water logged soil conditions. It is a reliable low risk crop. There are 250 known species of Eragrostis, or love grasses, but only a few are of significant agricultural value.


Teff is a very versatile grain. Teff flour can be used as a substitute for part of the flour in baked goods, or the grains added uncooked or substituted for part of the seeds, nuts, or other small grains. Due to it's small size, only 1/2 Cup of teff is needed to replace 1 cup of sesame seeds. It is a good thickener for soups, stews, gravies, and puddings and can also be used in stir-fry dishes, and casseroles.

Teff may be added to soups or stews in either of two ways:
1) Add them, uncooked to the pot a half-hour before serving time.
2) Add them cooked to the pot 10 minutes before serving. Cooked teff can be mixed with herbs, seeds, beans or tofu, garlic, and onions to make grain burgers. The seeds can also be sprouted and the sprouts used in salads and on sandwiches.

To cook teff place 2 cups purified water, 1/2 cup teff, and 1/4 tsp. sea salt (optional) in a saucepan. Bring to a boil, reduce heat and simmer covered for 15 to 20 minutes or until the water is absorbed. Remove from heat and let stand covered for 5 minutes.

Teff should be stored in a cool, dark, dry place in tightly covered containers such as glass jars. Cooked Teff can be kept in the refrigerator, but should be used within a few days.


This grain would be a worthy and healthful addition to your diet. Be creative, use your imagination, and enjoy this wonderful nutritious grain.


Following are two recipes adapted from packages of Arrowhead Teff.

Teff Pancakes
1 cup cooked Teff
1/4 tsp. Sea salt
1 cup multigrain pancake mix or whole grain flour
1 cup water or enough to make pancake batter
1 tbsp. Oil (optional)

Mix all ingredients; cook on a hot oiled griddle.
For variations try adding nuts, berries, or apples to the batter.


Teff Carob Cookies
3/4 cup rice flour
1/4 cup barley flour
1-1/2 tbsp. Carob powder
1/4 cup uncooked teff
1/4 cup molasses or maple syrup (or try brown rice syrup or agave syrup)
1/2 cup water or organic milk
1/4 tsp. Almond extract

Mix dry ingredients. Mix liquids. Combine mixtures. Drop small spoonfuls onto oiled baking sheet. Bake at 350º for 8-10 minutes.

Insect growth regulators (IGRs)

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Insect growth regulators (IGRs) are compounds that alter the normal growth process of insects and can therefore be used to control insect populations; these compounds interfere with insect metamorphosis, embryogenesis or reproduction. Among them we find compounds that mimic or antagonise insect juvenile hormone activity and substances that inhibit chitin synthesis in the exoskeleton.99 Juvenile hormone analogues provoke mortality at adult emergence, whereas chitin synthesis inhibitors cause mortality in larvae and nymphs; besides, both types of IGRs also cause sterilization in adult insects.


The main advantages of these compounds over other insecticidal substances are that they have a low mammalian toxicity and are often very species-specific insecticides:nevertheless they usually present a slow mode of action and sometimes a low stability.

Solid-phase synthesis of ciclopropane carboxylate moieties

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