Sum formula
| of these articles describes chemical sum formulas. For sum formulas in mathematics see collection of formulae algebra. |
In chemistry a sum formula serves for it, the summary composition of a molecule from the atoms or the amount of material relationship of a salt from the ions the appropriateTo indicate elements.
The sum formula of a material consists thus of the symbols of the contained chemical elements and small, numbers in deep position for their payment and/or. Amount of material conditions in this connection. This number of atoms stands as index always right below the atomic designation, howthe number is not written out „1 “thereby. The element of higher Elektronegativität (in the periodic system usually further right or above) stands in the sum formula like also in the name of the material usually right from an element lower Elektronegativität (why it e.g.Sodium chloride NaCl is called and not chlorine sodium connection ClNa).
Table of contents |
examples of sum formulas in chemistry
- NaCl, common salt, 1:1, H 2 O, consists water of
- sodium and chlorine ions in the quantitative proportion, however hydrogen - atoms (H) and an oxygen - consists atom (O) per molecule of two (2: 1),
- H 2 SO 4, sulfuric acid, consists even of twoHydrogen atoms, a sulfur - atom (s) and 4 oxygen atoms per molecule (7 atoms/molecule, relationship 2:1: 4).
for the history of the sum formulas
materials in form of most diverse indications already symbolized the Alchimisten. Jöns Jakob Berzelius led oneto today common symbol way of writing: The elements are formed by that or the two initial letters of latin of name of the element, e.g.:
- H for hydrogen (hydrogenium),
- O for oxygen (oxygenium),
- Fe for iron (ferrum),
- Outer one for gold (aurum) and
- Hg for mercury (hydrargyrum).
to the difference sum formula/structural formula
if - as in the common salt - elements in the quantitative proportion 1:1 is connected, existed common salt particles then out only in each casetwo atoms? The sum formula does not state anything over the structure of a connection from ions or also a molecule. In addition the structural formula is used (with simple molecules the sum formula is sufficient however for a clear description of the molecule).
To the meaning of sum formulas
sum formulas say something about the amounts of material - conditions out, in which elements together-find themselves with chemical reactions to connections. The output and final material of the reaction (Edukte and product) usually become in the reaction pattern in the form ofSum formulas inserted (usually the usual sum formulas are used here, itself from the symbols of the elements involved and/or. Build up for atomic places and small numbers in deep position (indices)). The latters give conditions to atomic's number and/or. Amounts of material n of the elements in theirrespective connections again:
- In common salt (sodium chloride) that is amounts of material - relationship from sodium to chlorine n (well): n (Cl) = 1: 1 (see. Illustration): one mol each sodium = 23 g and 1 mol of chlorine atoms = 35.45 g results inthus a mol common salt, amount of material relationship 1:1,
- in the water H 2 O is it n (H): n (O) = 2: 1,
- in the alumina aluminium 2 O 3 n (aluminium): n (O) = 2:3 and
- in the hexane C 6 H 14 n (C):n (H) = 6: 14 = 3 : 7 (the relationship formula of the same molecule therefore C 3 H 7, hexane would be has however the structural formula CH 3 CH 2 CH 2 CH 2 CH 2 CH 3, whichit shows that a chain of 6 carbon atoms and 14 hydrogen atoms is present.).
See also: Relationship formula, stoichiometry, reaction pattern, amount of material in mol
