A compound is a chemical substance composed of a specific set of atoms or ions. Two or more elements synthesize a substance through a chemical reaction to form a compound. All compounds are substances, but not all substances are compounds.
A compound can be a molecule or crystal in which atoms are joined together, in which atoms, molecules or ions form a lattice. Compounds based mainly on carbon and hydrogen atoms are called organic compounds, and other compounds are called inorganic compounds. Compounds containing a bond between carbon and metal are called organometallic compounds.
Compounds whose components share electrons are called covalent compounds. Compounds composed of oppositely charged ions are called ionic compounds or salts.
In organic chemistry, more than one compound has the same composition and molecular weight. Generally speaking, these are called isomers. Isomers usually have essentially different chemical properties and can usually be separated without spontaneously transforming into each other. A common example is glucose and fructose. The former is an aldehyde and the latter is a ketone. Their mutual conversion requires enzyme catalysis or acid-base catalysis.
However, tautomers are an exception: isomerization occurs spontaneously under ordinary conditions, so a pure substance cannot be isolated into its tautomers, even if these can be identified by spectroscopy, even under special conditions Be quarantined. A common example is glucose, which comes in open chain and ring forms. It is not possible to make pure open-chain glucose because glucose will spontaneously cyclize into hemiacetal form.
Chemicals versus chemical substances
All substances are composed of various elements and compounds, but these elements and compounds are often closely mixed together. The mixture contains more than one chemical substance, and they have no fixed composition. In principle, they can be separated into constituent substances through purely mechanical processes. Butter, soil and wood are common mixtures.
Gray iron metal and yellow sulfur are chemical elements, and they can be mixed together in any ratio to form a yellow-gray mixture. Since sulfur and iron can be separated by mechanical processes, such as using a magnet to suck iron away from the sulfur, this material can be identified as a mixture.
On the contrary, if iron and sulfur are heated at a certain ratio (1 sulfur atom of iron, or by weight, 56 grams (1 mole) of iron sulfur) 32 g (1 mole), a chemical reaction occurs to form a new substance, Sulfide composite iron (II), chemical formula Fez. The resulting compound has all the properties of a chemical substance, not a mixture. Iron (II) sulfide has its own unique properties, such as melting point and solubility. These two elements cannot be separated by normal mechanical processes; magnets cannot recover iron because there is no metallic iron in the compound.
