what is molecule:
A molecule is a group of atoms, same or different, which are kept together and cannot be separated without affecting or destroying substances properties.
There is an old concept that says that the molecule is the smallest part of a substance that retains its chemical properties and its composition. However, it is known today that the chemical properties of a substance are not determined by an isolated molecule, but by a minimum set of these.
Many known substances are made of molecules, such as sugar, water, and most of the gases, while other known substances are not molecular structure, such as salts, metals, crystalline networks, most of the glasses, and noble gases.
In chemistry, a set of at least two covalently bonded atoms forming a system stable and electrically neutral molecule is called.
Are examples of molecules: when two oxygen atoms combine to form a molecule of oxygen, and when a carbon atom (positive charge + 4) combines with two atoms of oxygen (negative charge – 2 each) to form a molecule of carbon dioxide.
There are various sciences that study the molecules. For example, almost all organic chemistry and inorganic chemistry much deal with the synthesis and reactivity of molecules and molecular compounds. Chemical Physics, and especially quantum chemistry also study the properties and reactivity of the molecules, and also quantitatively, where appropriate. Biochemistry is closely related to molecular biology, since both are studying living things at the molecular level.
The study of the specific interactions between molecules, including the molecular recognition is the field of study of supramolecular chemistry. These forces explain the physical properties such as solubility or the boiling point of a molecular compound.
Molecules that are constituted by the repetition of a comparatively simple unit or a limited set of these units, and reach relatively high molecular weights are macromolecules or polymers.
Molecular structure can be described in different ways. One of them is the molecular formula, which is useful for simple molecules such as H2O for water or for ammonia NH3. This formula contains the symbols of the elements present in the molecule, as well as their proportion (number of atoms) indicated by the subscripts. For more complex molecules, which are commonly found in organic chemistry, the chemical formula is not enough, and is worth using a structural formula or a skeletal formula, are that graphically indicate the spatial arrangement of functional groups.