Chemical compound
In chemistry, a compound is a substance formed from two or more elements, with a fixed ratio determining the composition. For example, water is a compound made out of hydrogen and oxygen in the ratio of two to one.
In general, this fixed ratio must be fixed due to some sort of physical property, rather than an arbitrary man-made selection. This is why materials such as brass, the superconductor YBCO[?], the semiconductor Aluminium gallium arsenide or chocolate are considered mixtures[?] or alloys rather than compounds.
A defining characteristic of a compound is that it has a chemical formula. Formulas describe the ratio of numbers of atoms in a substance. For example, in H2O (water) there are two hydrogen atoms for every one oxygen atom. The formula does not tell you that water is made of molecules. Indeed water ice has the same formula, but it is in the form of a crystal - there are no molecules in ice.
Compounds may have a number of possible phases. For a compound to be a liquid or a gas and still be called a compound, atoms from the various elements must be stuck together in the form of molecules. The formation of molecules is why compounds such as C2H4 exist (rather than just CH2) - the formula is telling you not just the ratios but also how many atoms there are in each molecule.
All compounds will break up into smaller compounds or individual atoms if you heat them to a high enough temperature. This temperature is called the decomposition temperature[?].
Every chemical compound that has been described in the literature carries a unique numerical identifier, its CAS number.
Types of compounds:
See list of compounds for a list of all compounds currently in Wikipedia.
divination from the stars, from spirits, from the shapes and complexions
of our nature to grasp at and anticipate future.html">future things, as if we had not
Sollicitis visum mortalibus addere curam,
si/sit.html">Sit subitum, quodcumque paras; sit coeca futuri
add this care, that they should know.html">know by, omens future slaughter?...
blind to fate in store; let it be permitted to the timid to hope."--
miserum est enim, nihil proficientem angi,"
["It is useless to know what shall come to pass; it is a miserable
Cicero, De Natura Deor., iii. 6.]
yet are they of much less authority now than heretofore. Which makes so
being lieutenant to King Francis I. in his ultramontane army, infinitely
the marquisate itself, which had been forfeited by his brother; and as to
his own affection opposing any such disloyalty, suffered himself to be so
were spread abroad everywhere in favour of the Emperor Charles V., and to
were so far believed, that at Rome great sums of money were ventured out
they made themselves of our ruin), that, having often bewailed, to those
he saw would inevitably fall upon the Crown of France and the friends he
misfortune, nevertheless, what constellation soever governed at that
divers passions; for having both towns and forces in his hands, the
suspecting his design, it had been in his power to have done more than he
Fossano only, and that after a long siege and a brave defence. --[1536]
"Prudens futuri temporis exitum
Ridetque, si mortalis ultra
.
On
wordlookup.net
All is still licensed under the GNU FDL.
It uses material from the wikipedia.
|
|