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The circumstances under which a compound will have ionic or covalent character can typically be understood using Fajans' rules, which use only charges and the sizes of each ion. According to these rules, compounds with the most ionic character will have large positive ions with a low charge, bonded to a small negative ion with a high charge. [25]
In contrast, the terms molecule or molecular formula are applied to molecules. [3] The formula unit is used as an independent entity for stoichiometric calculations. [4] [5] Examples of formula units, include ionic compounds such as NaCl and K 2 O and covalent networks such as SiO 2 and C (as diamond or graphite). [6]
For example, the compound dichlorine hexoxide has an empirical formula ClO 3, and molecular formula Cl 2 O 6, but in liquid or solid forms, this compound is more correctly shown by an ionic condensed formula [ClO 2] + [ClO 4] −, which illustrates that this compound consists of [ClO 2] + ions and [ClO 4] − ions. In such cases, the condensed ...
The resulting compound is called an ionic compound, and is said to be held together by ionic bonding. In ionic compounds there arise characteristic distances between ion neighbours from which the spatial extension and the ionic radius of individual ions may be derived. The most common type of ionic bonding is seen in compounds of metals and ...
Binary hydrogen compounds in group 1 are the ionic hydrides (also called saline hydrides) wherein hydrogen is bound electrostatically. Because hydrogen is located somewhat centrally in an electronegative sense, it is necessary for the counterion to be exceptionally electropositive for the hydride to possibly be accurately described as truly behaving ionic.
This is a list of common chemical compounds with chemical formulae and CAS numbers, indexed by formula. This complements alternative listing at list of inorganic compounds . There is no complete list of chemical compounds since by nature the list would be infinite.
Ionic compounds can also be produced from their constituent ions by evaporation of their solvent, precipitation, freezing, a solid-state reaction, or the electron transfer reaction of reactive metals with reactive non-metals, such as halogen gases. Ionic compounds typically have high melting and boiling points, and are hard and brittle.
Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. [1] Helium's first ionization energy of 24.57 eV is the highest of any element. [2]