The original definition of an "organic chemical", namely a compound that is derived from a natural, living organic source dates back to around 1850. This definition was already well-outgrown around 1900. During that time, chemists were synthesizing new organic compounds without any relation to living
organisms.
Nowadays, an organic chemical (or organic
compound) is described as:
Any compound containing one or more atoms of carbon
covalently bonded to atoms of other elements, most commonly hydrogen, oxygen or
nitrogen.
There are some exceptions to this definition; several simple
carbon compounds are considered to be inorganic chemistry,
such as carbon dioxide, sodium carbonate, hydrogen cyanide,
potassium cyanide, etc. On the other hand, all organic compounds do
contain carbon.
The simplest examples of organic chemicals are the straight
alkanes, such as methane, ethane, propane. Organic
compounds containing a hydroxyl group (an -OH group) are called
alcohols. Examples are methanol, ethanol,
propanol, isopropanol. There are many other classes of compounds in
organic chemistry, leading to an almost infinite number of organic
chemicals.
Describing organic compounds as more complex is a subjective
generalization; organic compounds can range from very simple
(e.g. methane) to highly complex (e.g.
fullerenes, DNA). However this is also true for inorganic
chemicals. For instance, silicon and sulfur can form complex
networks; zeolites are a common class of inorganic aluminosilicates
with highly ordened structures and hundreds of atoms per unit
cell.