Formula unit

A in the formula is a form of chemical formulas of compounds that are not composed of individual molecules. For inorganic substances, which are based on ionic bonds, creating a huge number of positive and negative ions, an ion lattice. The for this connection specified formulas ( formula units ) usually give to the abridged by the ratio of the atoms involved elements in the compound and comply in this respect a ratio formula. However, the compound contains a unit of formula and structural information is sometimes referred to as " resolved formula ". The formula unit of simple salts such as sodium chloride or magnesium chloride are shown in the form of NaCl and MgCl 2. In the first place, the cations, provided in the second place, the anions that are present in both the ionic lattices, as well as in aqueous solution (Na , Mg2 , Cl- ). More complex salts, consisting of polyatomic ions, the central atom and its ligands are referred to for the ions first, as in calcium phosphate Ca3 (PO4) 2 and ammonium sulfate (NH4) 2SO4 with the complex ion (NH 4) , (PO4) 3 - and (SO4) 2 -. Salts with inorganic acids, which contribute protons of the hydrogen atoms are treated as cations: sodium dihydrogen phosphate is given as a NaH2PO4. This is done in analogy to the usual formulas of inorganic acids in which the hydrogen atoms are given first ( eg H3PO4 for phosphoric acid), often resulting in their molecular structure [P (O ) (OH ) 3] does not do justice.

By the term formula unit is to be avoided, that is spoken in the treatment of chemical topics of molecules or particles, when no free molecules or particles are present.