ARTICLE 1

THE DEVELOPMENT OF THEORY OF ATOM

        

          Atoms are a basic unit of matter, composed of atomic nuclei and the negatively charged electron clouds that surround it. The atomic nucleus consists of a positively charged proton, and neutrons with neutral charge (except in the nucleus of Hydrogen-1 atom, which has no neutrons).

               The term atom comes from Greek (ἄτομος / átomos, α-τεμνω), which means it can not be cut or something that can not be divided again. The concept of atom as an indivisible component was first proposed by Indian and Greek philosophers. In the seventeenth and eighteenth centuries, chemists laid the foundations of this idea by showing that certain substances could not be further divided using chemical methods. During the late nineteenth and early twentieth centuries, physicists managed to discover the structure and subatomic components within the atom, proving that 'atoms' are not indivisible. The principles of quantum mechanics used by physicists then succeeded in modeling atoms.

1. The Atomic Theory of Jonh Dalton

            John Dalton put forward the hypothesis of atoms under the law of conservation of mass (Lavoisier) and the law of fixed comparison (Proust). Dalton's proposed theory: Atom is the smallest part of matter that can not be divided again. Atoms are described as very small solid spheres, an element having identical and different atoms for different elements. The atoms combine to form compounds with simple and integer ratios. For example water consists of hydrogen atoms and oxygen atoms Chemical reactions are the separation or amalgamation of the atoms, so that atoms can not be created or destroyed.

The atomic model of dalton The advantage of Dalton's theory is to start an interest in research on the atomic model.

The disadvantage is not to explain the relationship of oceans of compounds and electric current conductivity, if atoms are the smallest part of a element and can not be subdivided.

2. Atomic Model Joseph John Thompson

               Joseph John Thompson is the inventor of electrons. Thompson tried to explain the existence of electrons using his atomic theory and model. According to Thompson, the electrons are evenly distributed in atoms considered to be a positively charged ball.

    The atom model proposed by Thompson is often referred to as a model of raisin bread with bread as positively charged atoms and raisins as the electrons are spread evenly across the bread section. Atom as a whole is neutral.

3. Atomic Model Ernest Rutherford

               The study of alpha-light shooting on a thin gold plate allowed Rutherford to propose atomic theory and models to improve the theory and model of Thompson atoms. According to Rutherford, the atom has a positively charged nucleus and is the center of the mass of atoms and electrons around it.

               Rutherford found that the nuclei of positively charged atoms and electrons were outside the nucleus of the atom. However, Rutherford's theory and model of atoms also still have weaknesses: this theory can not explain the phenomenon of why electrons can not fall into the nucleus. Whereas according to classical physics, particles including electrons orbiting the path will release energy in the form of radiation so that electrons will orbit spirally and eventually fall to iti atom.

4. Atoms Model Niels Bohr

            Niels Bohr further refined the model of the atom expressed by Rutherford. Bohr's explanation is based on his research on the spectrum of hydrogen atomic lines.

Some of the things described by Bohr area. Electrons orbit at certain energy levels called skin
b. Each electron has a certain energy that matches the energy level of the skin
c. In a stationary state, the electrons do not release and absorb energy
d. Electrons can move from high energy levels to low energy levels and vice versa absorbing and releasing energy.

5. Atomic Model of Wave Mechanics

            The development of the latest atomic model proposed by atomic model based on quantum mechanics. This explanation is based on three theories namely The theory of the duality of electron particle waves proposed by de Broglie in 1924 Uncertainty principle expressed by Heisenberg in 1927 The wave equation theory by Erwin Schrodinger in 1926.

    According to this model of the atom, the electrons do not orbit on a particular path so that the path proposed by Bohr is not a truth. This atomic model explains that the electrons are in orbitals with a certain energy level. Orbital is the area with the greatest possibility to find electrons around the atomic nucleus.