1. 4-1 Early Ideas of the Atom
Democritus
Greek Philosopher
B.C.
Stated – Matter could be divided into smaller & smaller particles until it could no longer be divided.
Called these Particles – Atomos (indivisible)
Not based on any physical evidence, only thought.

2. Dalton’s Atomic Theory
Late 1700’s – John Dalton – School Teacher(england)
Dalton’s Atomic Theory – Summarized
All matter is composed of extremely small particles called atoms.
**Atoms of a given element are identical in size, mass, and other properties. (Isotopes - atoms same element with different mass.)
**Atoms cannot be subdivide, created, or destroyed.
Atoms of different elements can combine in simple, whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.

3. 3.2 Discovering Atomic Structure
Particle arrangement of the atom.
Protons (+)
Electrons (-)
Neutrons (0)
Michael Faraday
Made the connection between the atom and electricity.

4. J.J Thomson – Plum pudding
Used a Cathode Ray Tube (CRT)
Discovered electrons
Charge and mass
Electric current passed through low pressure gas in a glass tube.

5. Robert Millikan Millikan’s Oil-Drop Experiment
Proved the mass and charge of all electrons are identical.
By varying the charge on
different drops, he noticed
that the charge was always a
multiple of -1.6 x C.

6. Ernest Rutherford Used the Gold Foil Experiment
Marsden and Gieger performed the experiment
Bombarded thin sheets of metal with (+) charged particles.
Results of the Particle deflections
Most traveled through
Some Deflected in Both Directions
Very Few Deflected Back

7. Rutherford vs. Thomson
Plum Pudding
Nuclear

8. Rutherford results Atoms Contained a Nucleus Central part of the atom.
Very small and very massive = Very dense.
All the mass of an atom.
Positively charged, location of protons.

9. Protons and Neutrons E. Goldstein Sir James Chadwick
Used canal rays in a cathode ray tube to prove the existence of protons.
Positively charged particles that had significant mass moved towards the cathode.
Sir James Chadwick
Neutrons, were neutrally charged particles found in the nucleus to add mass to the atom and to act as “nuclear glue.”

10. Atoms are Empty Space
Most all of matter’s mass comes from the nucleus and that consist of a tiny central part of the atom. The remain space between the atom and the electrons is empty.

11. Summary of the Atom Nucleus Electrons Protons Neutrons
Positively charged particle found in the nucleus
Gives mass to the atom.
Neutrons
Neutrally charged particle found in the nucleus.
Gives mass to the atom and acts as “nuclear glue”
Electrons
Negatively charged particles that give the atom its size.

12. Properties of Subatomic Particles
4.2 How Atoms Differ
Properties of Subatomic Particles
Particle
Symbols
Relative Charge
Mass Number
Relative Mass
Actual Mass
Electron e- -1 u
9.11 x 10-28g
Proton p+ +1 1 u
1.67 x 10-24g
Neutron n0 u
1.68 x 10-24g

13. Atomic Mass Units (amu)
the equivalent mass of an atom.
Protons = 1amu
Neutrons = 1amu
Electrons = 0 amu

14. Subatomic calculations
Atomic Number (Z) –the number of protons within an atom. (Atomic # = p+)
Every element has its own unique atomic number.
p+ = e- , in an atom
Mass # = p+ + n0

15. Isotope Abbreviations
Atomic Symbol Notation:
X = atomic symbol
Mass Number form:
name of element – mass#

16. Isotope Form Practice
Write the element uranium with a mass # of 235 in atomic and mass form:
Mass # =
Atomic form =

17. Subatomic Particle Practice
How many protons, neutrons and electrons do the following contain?
Carbon – 13

18. Symbolic Form
Mass Form
Atomic #
Mass # p+ n0 e-

19. Mass Form
Symbol Form
Atomic number
Mass Number
# Neutrons
# Protons
# Electrons
Calcium - 41 24 Na 11 12 13 9 8 5 2
206 82
Silver-109
186 W 74

20. Isotopes
Atoms of the same element with different mass, due to the number of neutrons.
The number of protons determines the identity of an atom !!!!!!!
The number of neutrons can be different for the same type of element.
Hydrogen

21. Hydrogen Isotope Names
3 isotopes of hydrogen
Protium, Hydrogen – 1
Deuterium, Hydrogen – 2
Tritium, Hydrogen – 3

22. Relative Atomic Masses
Although we know actual masses of atoms it is more practical to use their relative masses
The arbitrary point – Carbon-12
1 atomic unit (a.u.) = Exactly 1/12 of C-12
All other atoms, weighed based upon Carbon-12

23. Atomic Mass
Average mass of all naturally occurring isotopes of an element.
Calculation
Atomic mass = (mass of each isotope)(% abundance)/100
Add the answers to each of the isotopes to get the average mass.

24. Modern Atomic Theory Determine the atomic mass of Oxygen. Isotope
Mass (amu)
% abundance
Oxygen – 16
99.762
Oxygen – 17
.038
Oxygen – 18
.200

25. Modern Atomic Theory

26. Modern Atomic Theory Determine the atomic mass of Uranium. Isotope
Mass (amu)
% abundance
Uranium-235
.720
Uranium - 238
99.280
Answer: Uranium =

27. 4.4 Unstable Nuclei and Radioactive Decay
Nuclear Reactions
Changes that occur within an atom’s nucleus.
Change the composition of the atom’s nucleus by altering the number of protons or neutrons.
Strong Nuclear Forces
Hold the nucleus together, neutrons help increase or add to this nuclear force.

28. 4.4 Changes in the Nucleus Radioactive Decay
Occurs when an atom emits one of the different forms of radiation.
The original nucleus decomposes,”decays,” to form a new nucleus.
The new nucleus will continue to decay until it reaches a stable configuration.

29. 4.4 Types of Radioactive Decay
Alpha Decay (Not a serious health hazard)
Nucleus ejects a helium nucleus, called an alpha particle, and becomes a smaller nucleus with less positive charge.
What would alpha decay of U-238 look like?

30. Alpha Decay

31. 4.4 Beta Beta Decay (100 times more penetrating than alpha)
The effect of turning a neutron in the nucleus into a proton, causing a beta particle (electron) to eject from the atom and the formation of a neutrino.
Write the equation for the beta decay of sodium – 24.

32. Beta Decay

33. 4.4 Gamma
Gamma Decay
High energy non-particle, with no charge or particle mass called a photon.
Caused by the nucleus changing to a lower energy level, releasing photons in the form of x-ray or other high end radiation.
Only stopped by thick concrete or lead.
Extremely dangerous.

34. Gamma Decay