Chemical compound

As a chemical compound is called a pure substance composed of two or more different chemical elements - are held together by interactions of electrons in a fixed number of atoms and hence mass ratio and so form a chemical bond - in contrast to mixtures. Characteristic of each chemical compound is its unique chemical structure. Often not clear is the molecular formula, with which you can calculate, for example, the quantity of products of a chemical reaction using molar mass ( in the stoichiometry, using a reaction scheme ). Isomeric chemical compounds have the same molecular formula, but a different molecular structure.

Types of chemical compounds

Coarse distinction is ionic, ie salt-like compounds and complexes, metallic and molecular compounds in the more than 80 million known chemical compounds. The subdivision inorganic / organic is fundamental, where as " organic" - with few exceptions - the carbon compounds are referred to. In 2002, about 16 million organic and inorganic compounds 3 million and 1 million polymers were known.

In principle, it is thus with regard to the nature of the bond between the elements involved four types of chemical compounds:

• Molecular weight compounds (typically made ​​of a non -metallic element, and one or more other non-metals )
• Ionic compounds (usually made ​​of a metal and one or more non-metals )
• Metallic compounds ( metal)
• Complex compounds ( metal cations and ions or molecules)

A more accurate distinction of compounds and their allocation to one of these four types may be carried out with the aid of the electronegativity difference of the elements involved in the bonding. In addition, there are transitional forms between the above four ideal types.

Molecular compounds

Molecular compounds are formed from non-metal and non-metal - they are non-conductors ( insulators ) (except diamond-like or plastic-like compounds with giant molecules ), usually with relatively low boiling point.

The smallest particles of molecular compounds are neutral atom associations (molecules). These consist of two atoms ( for example, in carbon monoxide, CO), composed of three atoms ( for example, in carbon dioxide) or even from a few thousand or tens of thousands of atoms ( giant molecules, polymers, for example, in plastic polyethylene or in the genetic molecule deoxyribonucleic acid DNA). The atoms in the molecules are linked by atomic bonds, that is, that the interconnected pairs of external atoms share electrons ( electron pair binding).

Examples of molecular compounds in addition to water and methane gas, sugar, carbon dioxide, polyethylene, etc.

Ionic compounds

Ionic compounds (salts ) consist of cations and anions. They are often salt-like:

• Brittle,
• Crystal form
• High melting and boiling points and
• Electrically conductive only in the melt or solution.

Ions (oxidation), which are then absorbed by the non-metal atoms resulting from the reaction of metal and non-metal atoms, characterized in that the metal atoms lose an electron ( reduction). The thus formed metal cations and non-metallic anions combine because of the electrical forces of attraction to ion crystals. According to one non-metals at different ionic compounds such as oxides ( oxygen anion), sulfides ( sulfur ), fluorides, chlorides, bromides, iodides, nitrides ( with nitrogen), carbides ( carbon ), hydrides ( hydrogen ), etc. Often oxygen is added as a third element; one then speaks of sulfates, chlorates, nitrates, carbonates, etc.

Examples of ionic compounds, iron (III ) oxide ( similar to the grate ), pyrite ( iron sulfide ), sodium chloride (salt ) and calcium sulfate (gypsum).

Intermetallic compound

Intermetallic compound ( often colloquially referred to as alloys) arising from metal and metal - they are:

• Electrically conductive,
• Good formability,
• Good conductors of heat and
• At room temperature mostly resistant.

The association of different metals to alloys can - be done in any proportions - especially when co- casting of metal melting.

However, if " intermetallic compounds " form, the elements involved in them only in very specific ratios include ( " intermetallic phase ", " stoichiometric composition ", see below stoichiometry ).

Examples of alloys are bronze ( copper and tin), brass ( copper, zinc) and copper nickel (as coinage ). Examples of intermetallic compounds are those between magnesium and germanium (formula: Mg2Ge ), the Al 2 Cu, the magnesium silicide Mg2Si, the bronze Cu4Sn and the cementite Fe3C ( iron and carbon, where it acts as a metal behaves ) and WC (tungsten carbide ).

Complex

Higher order compounds ( complexes) arise in a complex formation reaction mostly from non-ferrous metal cation and molecules with lone pairs (ligands). They are often strikingly colored.

Examples: The red blood pigment hemoglobin from ferrous ions and protein molecules and the deep blue Kupfertetrammin complex of cupric ion and ammonia.

Binary, ternary and quaternary compounds

Chemical compounds can be divided also on the number of involved chemical elements.

Binary compounds are composed of two different elements and have the general formula A x B y. Hydrogen chloride ( HCl), sodium fluoride (NaF ) and water ( H2O) are each composed of two elements together and are thus all binary compounds. The compounds may be molecular, ionic ( salts) or intermetallic compounds.

Analogously, ternary compounds of three different elements put together, such as sodium carbonate ( Na2CO3), which is composed of sodium, carbon, and oxygen.

A quaternary compound is, for example, potassium bicarbonate ( KHCO3 ).

The term primary connection, however, does not make sense, since by definition, chemical compounds must be composed of at least two elements. Different materials from only one element are called modifications. Occasionally, the term element compound is used.

Organic compounds

Molecular weight compounds, in which carbon is contained in conjunction with hydrogen are referred to as "organic ." They form the vast majority of all chemical compounds and are derived from the methane gas, the group of alkanes and hydrocarbons. In the hydrocarbon skeleton of organic compounds often are more atomic groups which affect the properties of the organic compound.

True to the carbon skeleton divided into organic compounds:

• Aliphatic hydrocarbons ( aliphatics, here under acyclic hydrocarbons, saturated (alkanes ), unsaturated (alkenes and alkynes ) and cyclic hydrocarbons)
• Aromatic hydrocarbons ( aromatics, divided into simple aromatic compounds and condensed aromatics )
• Heterocycles and
• Biochemical compounds ( alkaloids, amino acids, carbohydrates, proteins, steroids, terpenes, vitamins, etc. )

In line with the functional group shares one organic compounds in

• Oxygen and hydroxy compounds ( alcohols, aldehydes, esters, ethers, ketones, carboxylic acids, etc. ),
• Nitrogen compounds ( amines, amides, nitro compounds, nitriles ),
• Sulfur compounds ( alkanethiols, sulfides and disulfides, esters of sulfuric acid, sulfones, sulfoxides, thionamides, thiol, thioacid )
• Phosphorus compounds (phosphates, phosphines )
• Organometallic compounds.