the development of atom

1. The Development oF Atom Baharrani Dwi Kurnia 081211531133

2. From the time of ancient Greece to the present, the model and the atomic theory continues to evolve. Through the model and theory of the atom, we can determine the structure of an atom. The development can not be separated from efforts of scientists such as Democritus, John Dalton, JJ Thomson, Rutherford, Niels Bohr, Schrodinger, de Broglie and Heisenberg .

3. Democritus Aristotle and Plato were a very famous Greek philosopher who believed that matter could be divided into smaller and smaller pieces forever. He held a very strong influence on popular belief and his views on this were accepted for two thousand years. This theory was ignored and forgotten for more than 2000 years! Democritus was an ancient Greek philosopher who lived from 460 - 370 B.C.Democritus developed a theory of constituent materials “Democritus though that,“if you cut something in half again and again, you would at last have to stop. He said that this last piece of matter could not be cut any smaller. Democritus called these small pieces of matter atom.” (The Greek word “atomos” means not able to be divided or “indivisible)

4. Dalton In1803, the English scientist ,John Dalton born in Cumberland, United Kingdom reworked the Democritus’ theory.

5. J.J. Thomson In 1897, the work of an English scientist J. J. Thompson provided the first hint that atoms were made up of even smaller particles. Atoms are divisible “Dalton was wrong!’ J.J. Thomson discovered that atoms are made of smaller negatively-charged particles called electrons.

6. Thomson’s Cathode Ray Experiment Joseph John Thomson (1897) experiment on the effect of electric field and magnetic field in the cathode ray • Results of the experiments prove that there is a negatively charged particle in an atom because the beam can be deflected toward the positive pole electric field. based on the amount of deviation of cathode rays in an electric field, Thomson can determine the charge to mass ratio (value of e / m) of the cathode ray particles by 1.76 x 108 Coulomb / gram.

7. Rutherford • In 1910, the New Zealand physicistErnest Rutherford suggested that the positive charges of the atom were found mostly in its center, in the nucleus, and the electrons (e-) around it..Rutherford’s theory is based on the alpha ray scattering experiment by a thin gold plate.

8. Rutherford’s Theory • Rutherford’s Gold Foil Experiment Showed that : 1. Most of the mass of an atom and all of its positive charge is concetrate in a very small region in the center of an atom ( the nucleus ). The electrons orbit the nucleus like planets around the sun 2. Most of the volume an atom is empty space

9. The weakness of Rutherford Theory • “Can not explain why electrons do not fall into the nucleus. Based on theoretical physics, the motion of electrons around the nucleus is accompanied by emission of energy so long - eventually the electron energy is reduced and the longer the trajectory will approach the nucleus and falling into the nucleus.”

10. Niels Bohr • Niels-Bohr’s Atomic Model is referringto the weakness Rutherford’satomic model, around 1913 Niels-Bohr model of the atom tried to express that repair Rutherford’satomic model, which is known as Niels-Bohr model of the atom. • Bohr atomic theory stated in the postulates like : 1. Atom consists of a positively charged atomic nucleus as the center of mass of the atom and the electron revolves around the nucleus in specific energy levels (electron trajectory / shells / orbits).2.During the electrons moving on a stationary trajectory does not emit or     absorb energy (no change of energy).

11. Bohr’s Atomic Model Bohr model of the hydrogen atom describes the negatively charged electrons orbiting the atomic shell in a certain trajectory surrounds the positively charged atomic nucleus. When electrons jump from one orbit to another orbit is always accompanied by emission or absorption of electromagnetic energy hf. The weakness of Bohr’satomic model a. can not explain the Zeeman effect and the effect Strack.b. Can not explain the events of the chemical bond well, the effect of magnetic fields onatoms, and atoms are electron spectrum .

12. Modern Atomic • Electrons are found in orbitals, which are sometimes represented as clouds. • Orbitals are regions where there is a high probability of finding electrons of a given energy level. • We can never know the exact location of an electron, only the probability of finding it in a given location. • Erwin Schrodinger Wernerhesenberg