1. C HAPTER 11 “T HE ATOMIC M ODELS ”

2. M ODELS OF THE A TOM OBJECTIVES : Identify the inadequacies in the Rutherford atomic model.

3. M ODELS OF THE A TOM OBJECTIVES: Identify the new proposal in the Bohr model of the atom.

4. M ODELS OF THE A TOM OBJECTIVES : Describe the energies and positions of electrons according to the quantum mechanical model.

5. M ODELS OF THE A TOM OBJECTIVES: Describe how the shapes of orbitals related to different sublevels differ.

6. A TOMIC T HEORY OF M ATTER The theory that atoms are the fundamental building blocks of matter reemerged in the early 19th century, championed by John Dalton.

7. D ALTON ’ S T HEORY All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. Each element is composed of extremely small particles called atoms. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.

8. T HE E LECTRON Streams of negatively charged particles were found to emanate from cathode tubes. J. J. Thompson is credited with discovering the electrons (1897).

9. T HE A TOM, CIRCA 1900: “Plum pudding” model, put forward by Thompson. Positive sphere of matter with negative electrons imbedded in it.

10. M ILLIKAN O IL D ROP E XPERIMENT Robert Millikan (University of Chicago) determined the charge on the electron in 1909. Once the charge-to- mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other.

11. D ISCOVERY OF THE N UCLEUS Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles.

12. T HE N UCLEAR A TOM Since some particles were deflected at large angles, Thompson’s model could not be correct. Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. Most of the volume of the atom is empty space.

13. T HE B OHR M ODEL OF THE A TOM Niels Bohr I pictured the electrons orbiting the nucleus much like planets orbiting the sun. However, electrons are found in specific circular paths around the nucleus, and can jump from one level to another.

14. ATOMIC MODELS Bohr “planetary model” e- orbit in fixed energy levels and move from one level to another by gaining or losing only a certain amount of energy

15. To better explain his model, Bohr made use of the Quantum Theory, by M. Planck. M. Planck explained it by assuming that energy comes in packets called quanta. The wave nature of light does not explain how an object can glow when its temperature increases

16. F ROM THIS B OHR THEORIZED THAT : 1. electrons absorb or emit only whole #’s of energy 2. When an electron absorbs energy it becomes “excited” & moves to a higher level; when it releases energy, it drops back to a lower level 3. The lowest energy level an electron can occupy is called “ground state”

17. E NERGY ABSORPTION AND LIGHT EMISSION IN A B OHR ATOM When an atom absorbs energy, an electron is excited to a higher energy orbit. The electron then transitions back to a lower energy orbit and emits a photon of light.

18. C HANGING THE ENERGY Let’s look at a hydrogen atom, with only one electron, and in the first energy level.

19. Heat, electricity, or light can move the electron up to different energy levels. The electron is now said to be “ excited ” C HANGING THE ENERGY

20. As the electron falls back to the ground state, it gives the energy back as light C HANGING THE ENERGY

21. When “excited”, atoms produce a unique energy change that is used to identify it called “Spectroscopy“ If excited, atoms lose the energy gained to become “normal”