1. Atomic Theory
The thesis that all elements are composed of tiny, indestructible particles called atoms
All atoms of the same element are alike and have the same mass

2. How Small? How Big?
If an atom occupied a football field, the nucleus would be like a marble in the center.

3. Democritus (460 – 370 B.C.)
All matter is made of small, indivisible particles called “atomos” also know as atoms.
His model was a tiny, hard, uncuttable sphere.

4. John Dalton ( )
The ratios of the masses of elements in a compound can always be reduced to small whole numbers
Law of Multiple Proportions

5. Dalton’s Atomic Theory
1) all matter is composed of tiny particles called atoms
2) the atoms of an element are always identical while the atoms of different elements are different
3) compounds form when atoms combine; atoms combine in small whole number ratios
4) reactions involve reorganization of atoms; the atoms themselves do not change

6. Dalton Proposed the “Billiard-ball model” of the atom
His model was a solid, indivisible sphere

7. J.J. Thomson 1897
Produced a “cathode ray” which was deflected by a negative electric field
Thus the ray must be made of negative particles (electrons)
Thompson was awarded the 1906 Nobel Prize for his discovery

8. J.J. Thomson and Crooke
Since atoms are neutral, they must also have a positive area
Plum pudding model

9. Ernest Rutherford (1911)
Tests Thomson’s Plum Pudding Model by shooting alpha particles through a sheet of gold foil

10. Ernest Rutherford
Nuclear Model of the Atom

11. Protons were found to be 1836 X the mass of an electron
Charge of proton is +1

12. James Chadwick 1932
Discovered high energy particles with no charge and the same mass as the proton –
the neutron

13. Niels Bohr (1912)
Electrons “orbit” the nucleus somewhat like planets orbit the sun
Planetary Model

14. Arnold Sommerfeld Expanded the Bohr model
Electrons travel in orbitals, but
the orbitals are not the same shape
-- this leads to the electron cloud model of the atom

15. Electron Cloud Model

16. ERWIN SCHRODINGER
Was awarded the 1933 Nobel Prize for his Electron Cloud Model
His model was based on mathmatical probabilities, not a physical model.

17. Modern View of the Atom Tiny nucleus surrounded by electron “cloud”
Nucleus accounts for all of the mass
Arrangement of electrons causes different chemical properties

18. Electron Cloud Model
Note: Just as no map can equal a territory, no concept of an atom can possibly equal its nature. These models of the atom simply served as a way of thinking about them, though they contained limitations (all models do).

19. How do we know the identity of an element?
The number of protons (atomic #) distinguishes one element from another

20. Mass Number The total number of protons and neutrons in the nucleus
(protons + neutrons=mass number of an element)

21. Isotopes
Isotopes are atoms that have the same atomic number but a different mass number
Same element
Different numbers of neutrons in the nucleus
Ordinary Hydrogen
Deuterium
Tritium
proton
neutron

22. Atomic Mass The average mass of an element
Most elements occur as two or more isotopes in nature, and therefore have differing atomic masses—this is why the atomic mass is an average, each isotope is figured in to the average

23. What Can We See?
This is the surface of a platinum-nickel alloy as imaged by a Scanning Tunneling Microscope.
Vienna University of Technology
Light colors are closer, black deeper in the surface. The brighter blobs are the Ni atoms. The very large white blobs are surface impurities. Ni has 28 protons and 30 neutrons, which are not distinguishable.

24. An Alloy In The Process …
These are lead atoms working their way into copper to form an alloy.

25. Metals Hard Shiny – have luster Ductile Malleable
Good conductors of heat and electricity

26. Nonmetals
Dull
Brittle solids or gases at room temp.
Insulators

27. Metalloids They have properties of both metals and nonmetals.
Found on each side of the zig zag line between metals and nonmetals

28. Alkali Metal Group Group 1 or IA (except for H)
Most active metal group
Soft, shiny, very reactive with H2O
Wants to lose 1 electron

29. Alkaline Earth Metal Group
Group 2 or IIA
Harder than the alkali metals
Wants to lose 2 electrons

30. Transition Metals
Group 3-12 or IB-VIIIB

31. Halogens Group 17 or VIIA Most active group of nonmetals
Wants to gain 1 electron

32. Noble Gas Family Group 18 or VIIIA Inert
So stable they do not want to react with other elements

33. Periodic Law
The properties of the elements are periodic functions of their atomic numbers
Henry Moseley-arranged the periodic table by increasing atomic number (# of protons) instead of increasing atomic mass.

34. Period or series
Horizontal rows on the Periodic Table

35. Groups or Families
Vertical columns on the Periodic Table

36. The End