What is Molecule:
A molecule is a group of atoms, the same or different, that are held together and cannot be separated without affecting or destroying the properties of substances.
There is an ancient concept that says that the molecule is the smallest part of a substance that preserves its composition and chemical properties. However, it is known today that the chemical properties of a substance are not determined by an isolated molecule, but by a minimal set of these.
Many known substances are made up of molecules, such as sugar, water, and most gases, while other known substances are not molecular in structure, such as salts, metals, crystal lattices, most of the glasses, and noble gases.
In chemistry, a set of at least two covalently bonded atoms that form a stable and electrically neutral system is called a molecule.
Some examples of molecules are: when two oxygen atoms combine to form an oxygen molecule and when a carbon atom (positive charge +4) combines with two oxygen atoms (negative charge -2 each) to form a molecule of carbon dioxide.
There are several sciences that study molecules. For example, almost all organic chemistry and much of inorganic chemistry are concerned with the synthesis and reactivity of molecules and molecular compounds. Physical chemistry and especially quantum chemistry also study the properties and reactivity of molecules, and also quantitatively, where appropriate. Biochemistry is closely related to molecular biology, since both study living things at the molecular level. The study of specific interactions between molecules, including molecular recognition is the field of study of supramolecular chemistry. These forces explain physical properties such as solubility or the boiling point of a molecular compound.
The molecules that are constituted by the repetition of a comparatively simple unit or a limited set of said units, and that reach relatively high molecular weights, are macromolecules or polymers.
The 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 NH3 for ammonia. 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, such as those commonly found in organic chemistry, the chemical formula is not enough, and it is worth using a structural formula or a skeletal formula, they are the ones that graphically indicate the spatial arrangement of the different functional groups.