What are ionic compounds made of

Ionic bond explained simply: definition, example, properties

In addition to the covalent and metallic bonds, there is another bond between atoms, the so-called ion bond.

Definition: what is an ionic bond?

In the Ionic bond an electron passes from one reaction partner to the other and a new connection is created. These compounds typically consist of a metal and a non-metal and are commonly referred to as salts.

The reason why ionic compounds are formed by metals and non-metals is related to the electron affinity or the ionization energy. In order for an electron transfer to take place, the electrons must be willingly given up by one binding partner and readily accepted by the other binding partner.

The Electron affinity shows us how eagerly an atom accepts an electron.

The Ionization energy shows how gladly an atom gives up an electron.

In order for an ionic bond to come about, the electron affinity of one atom must be high. At the same time, the ionization energy of the other atom must be low. Typically, many metals have a very low ionization energy, while many non-metals have a very high electron affinity.

The grid energy

The Lattice energy is defined as the energy required to separate 1 mol of an ionic compound in the solid state into its ions in the gaseous state.

The lattice energy is usually given in kJ / mol and is positive for all ionic compounds. This means that energy has to be used to separate ionic compounds into their gaseous ions. Hence, it is one endothermic process, in which the system has to be supplied with energy.

Example of an ionic bond

Let us consider the example of the separation of the ionic compound sodium bromide (NaBr) into its gaseous ions. For this, an energy of 732 kJ per mole has to be expended.

This process can be noted as follows:

On the other hand, when a crystal lattice is formed, energy is released, precisely the amount of lattice energy.

Properties of ionic bonds

Ionic compounds can be distinguished from other compounds based on numerous properties. These properties include:

  1. high brittleness
  2. high hardness
  3. electrical conductivity (in solution or as a melt)

The Conductivity can be explained trivially because the ions present in the melt or solution can conduct electricity.

The hardness ionic compounds can be explained by the relatively high lattice energy. Since the attraction between the ions is very strong, a lot of energy has to be supplied to melt or vaporize the ionic compound. Sodium bromide, for example, has a melting point of 755 ° C.

Especially brittle are salts because they form a solid ionic lattice. If there are even slight shifts within this lattice, ions with the same charge stand opposite each other and repel each other - which corresponds exactly to brittleness.

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