A. Atomic Theory
Atomic theory has undergone a rapid advancement. There were many scientists proposing their theories which completing each other. Some of the scientist who had given important contributions to atomic theory were John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr. The atomic theory has also invited the contribution of some quantum physics pioneers such as the Broglie, Pauli, Schordinger, and Heisenberg.
1. Dalton’s Atomic Theory
The main ideas of Dalton’s atomic theory are :
a. Atom is part of an indivisible matter.
b. Atom of a certain element cannot change into another element’s atom.
c. Two or more atoms from different elements can be combined to form a molecule.
d. The atoms of different elements bounded in a molecule have a constant ratio. Its mass before and after a reaction is the same.
e. If two kind of atoms form two or more compounds, the ratio between them in the two or more compounds is just a simple value.
One of Dalton’s atomic theory mistakes is the statement that atom was a part of matter which is indivisible. You know that now it has been known the existence of electron, proton, and neutron which reside in the atom.
2. Thomson’s Atomic Theory
Joseph John Thomson had proposed an atomic model which stated that an atom is a solid ball with 10-10 m diameter has positive charges distributed over the whole part of the atom. The positive electric charges are then neutralized by electrons (negatively charge) distributed among the positive charge. The Thomson’s atomic model is called a pie model.
3. Rutherford’a Atomic Theory
Rutherford proposed an atomic model based on his experiment firing alpha particles a thin gold plate. If Thomson’s theory was right, then the alpha particle which its mass is 7000 times the mass of an electron should be reflected back. But, the fact is most of the alpha particles could penetrate the plate and just few other were reflected.
Based on this experiment result, Rutherford proposed an atomic model as follow.
a. An atomconsist of the positively charge nucleus which dominate the atomic mass.
b. Electron moves around the nucleus. The total value of negative electron’s charge is the same as positive nucleus’ charge so as a whole the atom is neutral.
c. The atomic nucleus and electron attract each other causing the centripetal force to emerge on the electron. This centripetal force keeps the electron on its orbit.
d. In a chemical reaction, there were only the outer-most electrons which influences each other, whereas the nucleus were unchanged.
Rutherford’s atomic model is better than Thomson’s because it was supported by experiment result. But, the Rutheford’s atomic model is in fact has weakness as follow.
a. Rutherford’s atomic model considered the electron radiates energy during its revolusion so that its radius will be smaller and smaller before it finally fall into the nucleus. It is not possible to occur..
b. Rutherford’s atomic model could not explain the discrete of the hydrogen spectrum. If Rutherford were right, then the hydrogen gas observed has to be continue due to its continue energy radiation. But, fact is that the hydrogen spectrum is discrete (discontinue).
Atomic theory has undergone a rapid advancement. There were many scientists proposing their theories which completing each other. Some of the scientist who had given important contributions to atomic theory were John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr. The atomic theory has also invited the contribution of some quantum physics pioneers such as the Broglie, Pauli, Schordinger, and Heisenberg.
1. Dalton’s Atomic Theory
The main ideas of Dalton’s atomic theory are :
a. Atom is part of an indivisible matter.
b. Atom of a certain element cannot change into another element’s atom.
c. Two or more atoms from different elements can be combined to form a molecule.
d. The atoms of different elements bounded in a molecule have a constant ratio. Its mass before and after a reaction is the same.
e. If two kind of atoms form two or more compounds, the ratio between them in the two or more compounds is just a simple value.
One of Dalton’s atomic theory mistakes is the statement that atom was a part of matter which is indivisible. You know that now it has been known the existence of electron, proton, and neutron which reside in the atom.
2. Thomson’s Atomic Theory
Joseph John Thomson had proposed an atomic model which stated that an atom is a solid ball with 10-10 m diameter has positive charges distributed over the whole part of the atom. The positive electric charges are then neutralized by electrons (negatively charge) distributed among the positive charge. The Thomson’s atomic model is called a pie model.
3. Rutherford’a Atomic Theory
Rutherford proposed an atomic model based on his experiment firing alpha particles a thin gold plate. If Thomson’s theory was right, then the alpha particle which its mass is 7000 times the mass of an electron should be reflected back. But, the fact is most of the alpha particles could penetrate the plate and just few other were reflected.
Based on this experiment result, Rutherford proposed an atomic model as follow.
a. An atomconsist of the positively charge nucleus which dominate the atomic mass.
b. Electron moves around the nucleus. The total value of negative electron’s charge is the same as positive nucleus’ charge so as a whole the atom is neutral.
c. The atomic nucleus and electron attract each other causing the centripetal force to emerge on the electron. This centripetal force keeps the electron on its orbit.
d. In a chemical reaction, there were only the outer-most electrons which influences each other, whereas the nucleus were unchanged.
Rutherford’s atomic model is better than Thomson’s because it was supported by experiment result. But, the Rutheford’s atomic model is in fact has weakness as follow.
a. Rutherford’s atomic model considered the electron radiates energy during its revolusion so that its radius will be smaller and smaller before it finally fall into the nucleus. It is not possible to occur..
b. Rutherford’s atomic model could not explain the discrete of the hydrogen spectrum. If Rutherford were right, then the hydrogen gas observed has to be continue due to its continue energy radiation. But, fact is that the hydrogen spectrum is discrete (discontinue).