Ionic bonding

The ionic compound ( also ionic bond heteropolar bond or electrovalent bonding) is a chemical bond, which is based on the electrostatic attraction of positively and negatively charged ions.

Description

The ionic bond was formulated around 1916 by Walter Kossel. From an electronegativity difference of ΔEN = 1.7 is called a 50 % partial ionic character. If the difference is greater than 1.7, therefore, are ionic bonds, including polar, predominantly covalent bonds ago. However, these are relatively arbitrary set limits, as is the case of the pure ionic bond is an idealization. As a rough guide: It is an ionic bond binding between the elements left in the periodic table ( PSE) are (ie metals ), and elements that are to the right in the periodic table ( non-metals ). If you look at the ion binding moiety, for example, of sodium chloride to which is often regarded as a classic case of ionic bonding, it is found a value of about 75 percent. Another example would be cesium fluoride with about 92 percent. Thus, ionic bonds have in all cases a proportion of covalent bonding. Conversely, this does not apply because within so-called element molecules exist the 100 percent covalent bond.

Electron configuration

The atoms strive by absorption or emission of electrons then to achieve the noble gas configuration and the lowest energy state for its outermost occupied shell. This is achieved either by electron donation from the elements with a lower electronegativity reached (left PSE), while simple or more positively charged cations are formed, or in the other case by electron uptake by the elements with higher electronegativity, and thus high electron affinity ( in the PSE right-wing elements ), while one or more times arise negatively charged anions.

Formation of the ion lattice

The cations and anions attract each other electrostatically; the energy released in the union of the two types of ions energy is called lattice energy and is the real driving force of the salt formation. The lattice energy is in this case composed of a total of 4 components:

• The zero point energy of the ions,
• The rejection energy between the cores on the one hand and between the electron shells on the other hand,
• The binding energy ( in ions with unsymmetrical charge distribution as NO2 ) results from London forces between more or less polarizable electron shells or multipole interactions and
• Finally, the Coulomb force between the oppositely charged ions.

The lattice energy can be determined empirically using the Born- Haber cycle.

Grid Properties

Since the electrostatic field extends equally in all directions in space produces very regular ionic lattice. Due to the different ionic radii, however, various ionic structures result: table salt (NaCl ), cesium chloride ( CsCl ), sphalerite (ZnS ) and fluorite structure (CaF2 ) and others which are named after the characteristic representatives. The relative stabilities of the different grids due to various types of coordination geometries and coordination numbers of the ions are reflected by the Madelung constants; this characteristic of the respective structure.

Characteristics of compounds having ionic bonding

• High melting and boiling points, as in crystals by the non-directional bonding forces, a relatively stable compound over the entire crystal is formed.
• Conduction current in the melt or in solution. The charge transport assume the ions. They will be discharged across the electrodes, whereby the salts are decomposed (often into its elements ). Therefore it is called ion conductor conductor 2nd order.
• Hard and brittle: In an attempt to deform a crystal plastic, this shatters the normal case, as in the crystal, the like-charged ions are pushed to each other and the bond is dissolved thereby.
• Crystal formation as a solid
• Ionic crystals are often colorless, because the valence electrons are most strongly bound and can be stimulated than that of visible light only by higher energy photons.
• Salts dissociate in aqueous solution in their corresponding ions; Ionic compounds dissolve in water - but in very varying degrees. For example, sodium chloride very readily soluble in water, but virtually insoluble silver chloride.