Chemical connection

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Here the concreteReason, why this article on the QA sides was registered:This article is inaccurate in parts and/or formulated unfortunate. The connection, the “red thread”, is missing likewise in some places. Discussion: Chemical connection Robert Bardolf 00:26, 19. April 2006 (CEST)

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chemical connection is thoseName for the co-operation of the smallest particles in chemical materials. The smallest particles can be atoms , anions , cations or molecules. From release and attaching chemical connections in a chemical reaction material with new characteristics results.

Table of contents 1 strong connections 1,1 Oktettregel and priority of the elements 1,2 a metal character in the periodic system 1,3 electrovalence 1,4 metallic binding 1,5 atomic bond (Kovalenzbindung) 2 weak connections 3 electrostatic attraction 4 spatial adjustment 5 connection length 6 bonding strength and binding energy 7 Web on the left of

Strong connections

of materials, which have strong connections, are characterised by high connection - or Gitterenergien . Thus high bloom and boiling temperatures result.

Kind of connection	connection partner
atomic bond (synonyms are Kovalente connection, connection of pair of electrons)	nonmetals (in complexes also ions)
electrovalence	of nonmetalsand metals
metallic binding	of metals

Oktettregel and priority of the elements

walter Kossel (1915) and Gilbert Newton Lewis (1916) developed the Oktettregel for the explanation of the numerical ratios of the elements in chemical connections. Therefore the element atoms are anxious, by chemical connectionthe noble gas next convenient in the periodic system - to reach configuration, in which they deliver or take up the appropriate number at electrons. The determining characteristic is thus the priority of the elements.

Examples:

• Fluor takes up an electron and receives as F ^-the configuration of neon.
• Calcium delivers two electrons and receives thereby the configuration of the argon.

The designation Oktett rule is derived from the eight bonding electrons of the noble gases.

This rule applies however only in the 1. and 2.Period of the main group elements without restriction. With the main group elements of the remaining periods also different configurations can be achieved. So the sulfur in the sulfuric acid has 12 electrons. The side group elements achieve occasionally different, relatively stable configurations.

a metal character in the periodic system

Within the periodic system the metal character of the atoms increases from left to right off and from top to bottom. One finds flowing transitions between the three kinds of connection accordingly, are involved to which metals and nonmetals. To the ion character that appliesresembles principle in reverse direction. For this some examples from the 3. Period:

within the connections of chlorine with the elements of the 3. Period of the periodic system decreases the ion character of the connections ever more andthe kovalente character too.

within the connections of the sodium with the elements of the 3. Period increases the metal character of the connections ever more off and the ion character ever more.

within the metal lattices or molecules of the elements of the 3. Period increases the metal character ever more off and the kovalente character.

according to thatOktettregel comes off a chemical connection formally by the fact that nonmetal atoms take up electrons as connection partners and metals electrons deliver one marks this as donor acceptor principle.

electrovalence

an electrovalence is trained between metal and nonmetal atom by the fact that the metal atomits bonding electrons completely to the nonmetal atom delivers. Thus a cation develops and from the nonmetal atom an anion from the metal atom. Due to the electrostatic attraction between these ions an ion lattice develops.

Example: Formal connection formation of calcium chloride

< math> \ cdot approx.\ cdot + 2 \ \ overline {\ underline {Cl cdot|}} \ rightarrow Ca^ {2+} + 2 \ overline {\ underline {|Cl|}} ^ - </math>

metallic binding

there during a metallic binding all connection partners of metals are, deliver also all atoms bonding electrons. The metal cations resulted from it become by the now freely mobile electrons(the so-called. Electron gas) held together, it develops a metal lattice.

Example: Formal connection formation of sodium as metal lattices

< math> \ mathrm {well \ cdot + \ cdot well \ rightarrow Na^+ \ left (: \ right) Na^+}< /math>

there atomic bond (Kovalenzbindung

) during an atomic bond all connection partners of nonmetals are,take up also all atoms bonding electrons. Thus develop molecules or atomic space lattices, which are held together by binding pairs of electrons.

weak connections

weak connections are usually formed between molecules and affected the specific physical characteristics such as simmering and fixed point. In macromolecules (for example Polypeptide) they appear also as internal-molecular connections. When very weak connections instead of the term connection the term reciprocal effect is used.

• Dipole dipole reciprocal effects between the molecules in liquid hydrogen sulfide;
• Dipole ion reciprocal effect when the releaseSalts in water, whereby the water dipole molecules form a hydrate covering around the ions;
• Van that Waals reciprocal effect between nonpolar Oktan - molecules.

When weak connections no complete electron jump or training can be formulated by binding pairs of electrons. Here only a shift of negative charge finds within a molecule instead of, whereby electrical dipoles develop, which can tighten other dipoles or ions (see polar atomic bond).

In proteins all kinds of the weak reciprocal effect as well as ion and atomic bonds can occur also within only one Polypeptid - molecule.

Electrostatic attraction

all chemical connections and reciprocal effects can be attributed to electrostatic attraction between opposite charges.

Binding type	positively charged	negatively charged
electrovalence	cations	anions
metallic binding	cations (also „atomic trunks “mentioned)	freely mobile electrons between the cations (also as „electron gas“) atomic bond
of atomic nuclei	electron sheath	hydrogen bond
designates	positively polarized hydrogen atom O, N or F with at least	a not-binding pair of electrons dipole dipole reciprocal effect positively polarized atom of a molecule negatively polarized
atom	of a molecule dipole ion reciprocal effect positively polarized	atom by connection at O
,	N or Fa molecule	anion
Van that Waals connection	positively polarized atom of a molecule	negatively polarized atom of a molecule

explanations to the overview:

• Lattice federations are formed only in the solid state. In the liquid condition the lattice breaks down, the particles is more easily against each other adjustable, thatA connection character remains however.
• From the electrovalence an ion lattice results. Example common salt NaCl with sodium cations well ⁺ and chloride anions Cl ^-.
• From the metallic binding a metal lattice results. Example: Copper cu, brass (copper zinc an alloy); Mercury is at room temperaturein addition, liquid, leads in this condition the electric current.
• For atomic bond see there
• hydrogen bonds are usually between-molecular reciprocal effects. In ice a molecular lattice is present, likewise in sugar (Saccharose) with room temperature below 0 °C (crystal sugar).
• Dipole dipole reciprocal effects arise between polar molecules, which do not fulfill the conditions for a hydrogen bond. Example: Ether: H ₃ C-O-CH ₃
• ion dipole reciprocal effects arise among other things when dissolving salts in water. The water dipoles surround the ions as And it prevents hydrate covering by the fact that cations and anions join themselves again to a lattice federation.
• Van that Waals reciprocal effect develops between nonpolar molecules, which polarize themselves during approximation mutually, it develops induced dipoles (contrary to the permanent Dipol-Molekülen such as water and hydrogen sulfide). Example:Atomic federations in liquid noble gases, molecular lattices of the iodine at room temperature, π complex with the Bromierung of the Ethens.

spatial adjustment

in molecules and atomic space lattices is dependent the spatial adjustment of the connection partners of geometry of the atomic orbital. (Detailssee in addition under atomic bond.)

in metal and ion lattices depends the spatial structure on the size of the connection partners, which arrange themselves on a meant Kugeloberfläche. (see in addition Kugelpackung, crystal structure).

Permanent or induced Dipolmoleküle arrange themselves to each other in such a wayout that their molecule parts loaded opposite to each other wise and the parts with same Partialladung as large a distance as possible from each other have.

connection length

this is the center distance of the atoms or ions when chemical connections.

With crystalline Solids with ion or metal lattices the distances of the lattice components can be determined by Roentgen - or electron diffraction. Since in crystal lattices different distances of the network levels can be measured, in tables the smallest distance is usually indicated as connection length.

In Kalziumfluorid amounts to the distance between the calcium cations approx. ²⁺ and the fluoride anions F ^- 235 pm. In metal lattices the distance amounts to depending upon atomic size between 200 pm and 500 pm.

For atomic bond see there

hydrogen bonds point depending upon polarization degreesDistances between 120 pm and 300 pm up.

bonding strength and binding energy

a connection are all the stronger, the more energy with its education become free. Turned around applies also: The more strongly a connection is, all the more energyto solve around it and is all the less reactive the connection or the element must be spent.

As binding energy for ionic compounds the lattice enthalpy is indicated, that is the enthalpy, which must be spent, around a firm crystal into thoseTo transfer gaseous phase, in which the ions are freely mobile.

The lattice enthalpy depends on the one hand on the size of the ions involved: The more largely the ions, the smaller is the Gitterenergie, there the attraction with increasing distance of the positive cores ofdecrease to the negative electron sheath of the connection partner.

Examples: Lattice enthalpy of the fluorides of the alkali metals with 25 °C in kJ per mol:

Name	formula	ion radius of the univalent alkali metal cations X + in pm	lattice enthalpy
Lithiumfluorid	ran	74	1039
Natriumfluorid	NaF	102	,920
potassium fluoride	Key-field	138	,816
rubidium fluoride	RbF	149	,780
cesium fluoride	CsF	170	,749

on the other hand depends the Gitterenergie on the electrical charge of the ions involved: The more largely the charges, the more largely are the attraction and all the more largely are the Gitterenergie.

Examples:Lattice enthalpy with 25 °C in kJ per mol (in the examples the ion radius changes only little):

Name	formula	cations	anions	lattice enthalpy
sodium chloride	NaCl	well +	Cl -	920
magnesium chloride	MgCl 2	mg 2+	Cl -	2502
Natriumsulfid	well 2S	well +	S 2	2207
magnesium sulfide	MgS	mg 2+	S 2	3360

the highest lattice enthalpy exhibits alumina aluminium ₂ O ₃ (aluminium ³⁺ and O ²) with 15157 kJ/mol.

For the attraction K between two loaded oppositeThe mathematical relationship applies for ions with the charge quantity of e1 and e2 in the distance r

As measure for the bonding strength during the metallic binding the fusing temperature can be used: The more highly the fusing temperature, the stronger are the binding forces. these depend again both on the distance of the metal cations and on the number of the delivered electrons: The more bonding electrons will deliver and the smaller the lattice spacing, all the more largely are the binding forces and thus the fusing temperatures.

Name	Formula of the metal cation	lattice spacing in pm	fixed point in °C
sodium	well +	430	98
potassium	K +	530	63
calcium	approx. 2+	550	,851

the connection enthalpy of the atomic bond is by the change of enthalpy with the dissociation of molecules into its atomsin the gaseous phase defines. It depends, like the connection length (see above), both on the size of the bound atoms and on the number of the binding pairs of electrons: The more largely the radius of the connection partners, the more largely is their distance andthe binding energy is the smaller. When connections between homogeneous atoms it shows itself that their distance depends also on the number of the binding pairs of electrons:

Name	formula	connection	connection length in pm	connection enthalpy in kJ per mol
chlorine	Cl 2	Cl-Cl	199	It applies
for 242	bromine Br	2	Br-Br	228
,193	Ethan C 2 H	6	CC	154
,348	Ethen C 2 H	4	C=C	134
,614	Ethin C 2 H	2	C≡C	120

,839 for delokalisierte atomic bonds accordingly that it more low-powered asa Mehrfachbindung, but than a single bond are higher-energy. Thus the connection enthalpy in the benzene amounts to 147 kJ/mol.

The inter+molecular reciprocal effects have only 10% of the bonding strength of the strong connections. Nevertheless they have a strong influence on firm and Kochpunkte thatMaterials:

During the hydrogen bond the connection enthalpy amounts to with strong polarization of the connection partners at least 40 kJ/mol, with weak polarization at the most 20 kJ/mol. It is responsible for it that the point of simmering of water is with 100 °C, during the boiling point of hydrogen sulfide - 83°C (see anomaly of boiling point)

the strength of the ion dipole reciprocal effect amounts to results from the formula

e ₁: Ion charge </br> µ ₁: Dipole moment< /br>

The strength of the dipole dipole reciprocal effect results from the formula

µ _1,2: Dipole moments

the connection enthalpy of the Van derWaals reciprocal effect lies during an order of magnitude of 1 kJ/mol. Their amount depends on the dipole moment of the particles. Since it concerns induced dipoles however here, also the polarizability that plays firstnonpolar atoms a role: Large one „yields “atoms can more easily be polarized than small „hard “. This can be read off from the boiling points of the noble gases, which train stronger Van that Waals reciprocal effects with increasing size increasingly and so that increasingly need more energy, around these attractionto overcome and go over into the gaseous phase.

Name	formula	atomic radius in pm	boiling point in °C
helium	He	122	-269
neon	Ne	160	-246
argon	acre	191	-186
krypton	Kr	198	-152
xenon	Xe	216	-108
radon	Rn		-62

the boiling pointsnonpolar molecules depend however also on the surface, with which they can exercise Van that Waals reciprocal effects to neighbouring molecules. Thus the boiling point of the linear, normal n of pentane amounts to 36.1 °C, while that isomers 2,2-Dimethyl-propan with the same molecular mass a boiling pointfrom 9,5 °C has, since it is almost spherical and so that a smaller „contact surface has “to neighbour molecules.

With small binding energy, which comes mainly by electrical attraction, one speaks of Physisorption. To the Physisorption e.g. belongs. the Van that Waals connection or the hydrogen bond.

With larger binding energy one speaks of chemisorption, with which overlap the electron orbital involved and lead in such a way to a connection. To the chemisorption the kovalente atomic bond and the complex connection belong.

Of Physisorption one speaks with binding energy in the m eV - range, from chemisorption within the eV-range and more largely. An exact border between both is often not possible.

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• extensive explanations for chemical connection