Chemische Verbindung
In der Chemie, bezeichnet man mit Verbindung eine Substanz, die aus zwei oder mehr Elementen besteht, die in einem festen Mengenverhältnis zueinander stehen.
Somit zählen Legierungen (z.B. Messing) oder andere Stoffgemische (z.B. Schokolade) nicht zu den chemischen Verbindungen.
A defining characteristic of a compound is that it has a Formel. Formulas describe the ratio of numbers of atoms in a substance. For example, in H2O (Wasser) there are two hydrogen atoms for every one oxygen atom. The formula does not tell you that water is made of Molekülen. Indeed water Eis has the same formula, but it is in the form of a Kristall - there are no molecules in ice.
Compounds may have a number of possible Aggregatzustände. For a compound to be a Flüssigkeit 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 ethene|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.
Types of compound: Salze, Oxides, Organische Verbindungen
See Liste von chemischen Verbindungen for a list of all compounds currently in Wikipedia.