1. Chemistry: Matter and Chemical Bonding Early Atomic Theories

2. Timeline.....  Ancient Greeks (approx 450 BC)  "Four Element" Theory – Earth, Air, Fire, Water

4. Benefits:  First suggestion that substances were actually made up of a combination of different "elements."

5. Democritus:  400 BC – Democritus  "The smallest indivisible particle of matter is the 'atom' "  No evidence – based on thought  However, the "4 element" theory lingered for almost 2000 years! (YIKES)

6. Democritus’ Model

7. John Dalton (1809)  All matter is composed of indivisible particles called atoms.  All atoms of a given element are identical; atoms of different elements have different properties.  Chemical reactions involve the combination of atoms, not the destruction of atoms.  When elements react to form compounds, they react in whole-number ratios.  Dalton's atomic theory supported previous research. Lasted almost a century!

8. Model: Indivisible billiard ball

9. J.J. Thomson (1897)  Used the work of other scientists that showed that atoms contain charges, and his own work with cathode ray tubes, to develop a modified atomic theory.  Atoms are positive spheres, with negative particles (electrons) embedded in them.

10. Model: Raisin bun

11. Ernest Rutherford (1911)  Student of Thomson – disagreed. Gold Foil Experiment:  Alpha radiation (positive) were shot at a piece of gold foil.  Most of the alpha particles passed through the foil, suggesting that most of matter is empty space!  Some particles were deflected back at angles; they had come in contact with something very dense!

12. Gold Foil Experiment:

13. Leading to…..Nuclear Model:  Rutherford – dense core of positive charge (nucleus), with negative electrons orbiting around the nucleus.  Later experiments showed that the positively charged particles, now called protons, have an equal but opposite charge to the electrons, and have a mass 1836 x greater!  The neutron and the existence of isotopes were also discovered

14. Niels Bohr  Worked with Rutherford  Used atomic spectrum information to place electrons in energy levels around the nucleus

15. Spectroscope:

16. How it works….  Each element has a unique emission spectrum  When electrons are given energy, they jump to a new energy level  When they fall back down, they emit this extra energy as light  Lines on an emission spectrum represent jumps between energy levels. DEMO

17. Emission Spectra:

18. Modern View of the Atom  Dense nucleus containing: (+) protons Neutral neutrons  Shells of small (-) electrons orbiting the nucleus 2 e - in 1 st orbital 8 in 2 nd 8 in 3 rd (until next year)

20. Subatomic Particle ChargeLocationSize Proton (p + )PositiveNucleus1 Neutron (n 0 )NeutralNucleus1 Electron (e - )NegativeIn Orbit 1_ 2000

21. Atomic mass / Mass Number -Use rounded values -26.98 -> 27 -28.09 -> 28 -30.97 -> 31 Atomic Number = # of protons = # of electrons in a neutral atom Mass number = protons + neutrons

22. Isotopes  Atoms of the same element have the same # of protons  The # of neutrons can differ  The same element with a different # of neutrons are called isotopes  Radioisotopes are unstable and decay creating radioactivity  Average atomic mass takes the masses of all isotopes into account.

23. Standard Atomic Notation C  mass # is 12  atomic # is 6  therefore, this carbon has 12 - 6 = 6 neutrons 6 12

24. GROUPS ON THE PERIODIC TABLE

25. Your Turn  Subatomic Particle Worksheet  Read 6.4 Define: Chemical Family, Periods, Dmitri Mendeleev  “Try this” on page 224  Homework P. 225 Q: 1-6, 8-11