Understanding Molecular History
Although the presence of molecules has been accepted by many chemists since the early 19th century, there are some disagreements among physicists such as Mach, Boltzmann, Maxwell, and Gibbs, who see molecules as a mathematical conception. Perrin's work on Brownian motion (1911) is considered the final proof to convince scientists of the molecule.
Likewise, the definition of molecules has changed along with the development of knowledge about molecular structure. Molecules as the smallest particles of chemicals that still maintain their composition and chemical properties. This definition is often applied because many material resources such as rock, salt, and metal consist of a network of atoms and ions which are chemically bound and not composed of discrete molecules.
Understanding Molecules
Most molecules are too small to be seen with the naked eye. Exceptions are contained in DNA which can reach macroscopic size. The smallest molecule is diatomic hydrogen (H2), with an overall length of about twice the binding molecule (0.74 Å). A single molecule usually cannot be monitored using light, but can be detected using an atomic microscope.
Very large molecules, called macromolecules or supermolecules. The effective radius of the molecule is observed for the size of the molecule in solution.
Molecular Size
Most molecules are very small to be seen with the naked eye. Exceptions are found in DNA which can reach macroscopic size. The smallest molecule is diatomic hydrogen (H2), with the whole molecule about twice the bond length (0.74 Å). A single molecule usually cannot be monitored using light, but can be detected using an atomic force microscope. Very large molecules are called macromolecules or supermolecules. Effective molecular radius is the size of a molecule that is monitored in solution.
Molecular Formula
Empirical compound formulas show the simplest elemental comparison values of these compounds. For example, water always has a ratio value of hydrogen oxygen atoms compared to 2: 1. Ethanol also always has a ratio value of carbon, hydrogen, and oxygen 2: 6: 1.
However, this formula does not indicate the shape or arrangement of atoms in a molecule. For example, dimethyl ether also has the same value as the ethanol ratio. Molecular constituents with the same atomic number but different arrangements are referred to as isomers.
It should be noted that the empirical formula only gives a comparative value of the constituent atoms in a molecule, and does not provide the true value of the number of atoms. The molecular formula describes the number of atoms that make up the right molecule. For example, acetylene has the molecular formula C2H2, but the CH formula is empirical. Molecular mass can be calculated from chemical formulas. Often the molecular mass expressed in atomic mass units is equal to 1/12 of the carbon-12 atomic mass.
Molecular Geometry
Geometrically shaped molecules remain in a state of equilibrium. The bond length and bond angle will continue to vibrate through vibrational and rotational motion. Chemical formula and molecular structure are two important factors that determine the properties of a compound.
Isomer compounds have the same chemical formula but different properties for different structures. Stereoisomer is an isomer which has physical and chemical properties which are very similar in biochemical but different activities.