4. All matter is composed of atoms Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the constituent elements Atomic theory proposed by John Dalton
21. The model created by Rutherford had still some serious discordance. According to the classic science, electron moving around the nucleus should emit an electromagnetic wave. Electron should than move not by the circle but helical and finally collide with the nucleus. But atom is stable.
23. Rutherford also realized that the nucleus must contain both neutral and positively charged particles. The neutron was then discovered in 1932 by Chadwick .
25. Following Rutherford’s planetary model of the atom, it was realized that the attraction between the electrons and the protons should make the atom unstable Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special quantized locations
27. Subatomic particles Electron Proton Neutron Name Symbol Charge Actual mass (g) e - p + n 0 9.11 x 10 -28 1.67 x 10 -24 1.67 x 10 -24
29. In the Bohr model, the electron can change orbits, accompanied by the absorption or emission of a photon of a specific color of light.
30. Bohr’s Model 1913 – Atomic Model with Fixed Orbits proposed – The Atom has No Charge Number of Protons = Number of Electrons
31. An easy way to calculate the total number of electrons that can be held by a given energy level is to use the formula 2*n 2 , 98 7 72 6 50 5 32 4 18 3 8 2 2 1 Maximum number of electrons 2*n 2 Principle energy level ( n )
32. The most electrons possible in the first shell are 2. After the first shell is filled, the second shell starts filling up, according to the number of positive charges in the nucleus. The most allowed in the second shell is 8 electrons. Then the third shell starts to fill.