1. Unit 2.1 Notes
From class

2. History of the
Atom

3. History of the Atom

4. Aristotle
4 Elements
FIRE
AIR
WATER
EARTH

5. Democritus

6. Modern Atomic Theory

7. John Dalton 1766-1844 English School Teacher
Experiments to test atomic theory
Studied ratio in which elements combine

8. Dalton’s Atomic Theory
1. All elements are composed of tiny invisible particles
Atoms
2. Atoms of the same element are identical
3. Atoms of different elements can physically mix together/ chemically combine
Simple whole number ratios  compounds
4. Chemical reactions occur when atoms are separated, joined, or rearranged

9. J.J. Thompson

10. Cathode Ray Tube Glowing beam between electrodes Cathode  anode
(-)  (+)
Ray attracted to the positive charged plates
Bends toward positive

11. Electron Discovered e- in 1897
Negative particle
J.J. Thompson (1856 – 1940)
Discovered e- in 1897
Pass an electric current through gas at low pressure
Mass 1 /2000 the mass of the H atom
Millikan

12. E. Rutherford

13. Atomic Nucleus University of Manchester, England Alpha particles
Ernest Rutherford (1911)
University of Manchester, England
Alpha particles
He that has lost 2 e-
2p + 2n
Directed a narrow beam of alpha particles at a thin sheet of gold foil
Some pieces went through, while others were bounced backwards

14. See experiment Atom is mostly empty space
Rutherford’s experiment
Atom is mostly empty space
Positive charge & most of the mass is concentrated in the center
Nucleus
Central core
Protons & neutrons
Small compared to entire atom

15. N. Bohr
1. Electrons travel in fixed paths around the central, positively charged nucleus.
ORBITALS / SHELLS
2. Energy Levels – energy
is lost or gained when
electrons move from one layer to another
- Light given off
3. Atom is mostly empty space

16. J. Chadwick Discovered the neutron
Neutron’s mass is nearly equal to the mass of a proton

17. Neutron Composed of a proton + an electron Overall neutral charge
James Chadwick (1932)
Latest theory
Composed of a proton + an electron
Overall neutral charge

18. Quantum Mechanical Model
Electrons are not in rings.
Heisenberg Uncertainty Principle – electron position can not be observed but can only be predicted.
Electron is a particle that acts like a wave.

19. Orbitals
4 Types of Orbitals
s, p, d, f

21. Dmitri Mendeleev Russian Scientist Built Periodic Table
- atomic masses
Using his table, was able to predict missing elements

24. Henry Moseley Englishman
1914 – Reordered the elements of the Periodic Table
Atomic Number
= # of protons

28. Modern Periodic Table

29. Atom
Smallest particle of an element that retains the properties of that element

30. Proton Positively charged particle
Mass is 1840 times the mass of an e-
E. Goldstein (1886)
Rays traveling in opposite direction of cathode ray
# Determines which atom

31. Cathode Ray Tube Glowing beam between electrodes Cathode  anode
(-)  (+)
Ray attracted to the positive charged plates
Bends toward positive

32. Atomic Number # protons in the nucleus Neutral atom Same # p as # e
Atoms are different due to the number of e, p, n in each atom
Atomic #
# protons in the nucleus
Neutral atom
Same # p as # e
Determines position on the periodic table
Periodic Table of the Elements

33. Mass Number # of protons + # of neutrons
The mass of the atoms is concentrated in the nucleus
Found at the bottom of the element’s square
Periodic Table of the Elements

34. Isotopes
Hydrogen
Deuterium
Tritium

35. Isotopes
Atoms that have the same # protons but different # of neutrons
Each isotope will have a different mass #
Nature of the element is a combination of the various isotopes
Behave chemically the same for the same element
Due to p & e

36. How Do You Write An Isotope
mass # A X
element Z
atomic #

37. # neutrons = mass # - atomic #
Writing Isotopes
Carbon-12
Carbon-13
Oxygen-16
Oxygen-17
Oxygen-18
Chromium-50
Chromium-52
Chromium-53
# neutrons = mass # - atomic #

38. Average Atomic Mass
Average of all the masses of the know isotopes of an element

39. S Orbitals
S orbital
Groups 1A & 2A
2 electrons
Spherical

40. P Orbitals Groups 13A – 18A 6 electrons total 2 e- in px 2e- in py
2e- in pz

41. D Orbitals – 10e-

42. F Orbitals