1. Ch. 4 Atomic Structure
4.1 Defining the Atom

2. Early Models of the Atom
Democritus’s Atomic Philosophy
He believed atoms were indivisible and idestructible.
Philosophy because there is no experimental support
video

3. Dalton’s Atomic Theory
John Dalton ( )
Theory because he had experimental support

4. Dalton’s vs. Modern Atomic Theory
Elements are composed of tiny, indivisible atoms.
Atoms of same element are identical
Different elements can mix or react to make compounds.
When chemical reactions occur, elements rearrange but no new elements.
Elements are made of atoms BUT atoms are divisible.
Atoms are not absolutely identical. Isotopes – different mass but same properties.
Same as Dalton’s

5. 4.2 Structure of the Atom

6. Location of Particles Nucleus (positive charge)
Protons and Neutrons
Electron Cloud (negative charge)
Electrons video

7. Discovery!! Electrons Electrons were discovered:
by J.J. Thomson in 1897 (don’t memorize date)
Through experiments with a cathode ray tube
Determined existence, negative charge and mass
video

8. Protons and Neutrons Discovered!
Protons were discovered:
By Eugene Goldstein in 1886
Also through the use of cathode ray tubes
Discovered positive charge
Neutrons were discovered:
By James Chadwick in 1932
By bombarding boron with alpha particles
Discovered no charge

9. Nucleus Discovered!!
Atomic theories: Chocolate chip cookie dough theory: Protons, neutrons were dough and electrons choc. Chips spread throughout.
Rutherfords Gold Foil Experiment
Bombarded gold foil with alpha particles and found some of the particles rebounded.
Must be small hard center in middle of atom

10. Gold foil experiment
Click on the above link.

11. Analogy
Rutherford’s experiment v. firing a gun

12. Nucleus size
Nucleus v. electron cloud
Do you see the tiny star? *

13. Distinguishing among Atoms
Ch. 4.3
Distinguishing among Atoms

14. Atomic Number/Mass Number
Atomic Number: small whole number
Atomic Mass/Mass Number: larger (numerically) number with decimal

15. Atomic Number/ Mass Number
Atomic Number: # of p+ (in neutral atom also # of e-)
Mass Number (rounded): # of p+ + # of n0
To find # of n = Mass # - Atomic #
How many p, n, e- does Fe have?

16. Isotopes
Isotopes have the same atomic number but different mass number.
What changed? Number of ____ changed.

17. Ions (not on website) Ions: charged atoms
Ions: gain or lose ELECTRONS to become charged
Cation: positively charged atom: lost e-
Anion: negatively charged atom: gained e-

18. Ways to show isotopes Name-mass number Symbols of isotopes of carbon:
Carbon-14 = isotope of Carbon-12
Symbols of isotopes of carbon:

19. Atomic Mass
Atomic Mass: weighted average mass of all isotopes of an element.
Same number as mass number (not rounded)
Measured in a.m.u. = atomic mass unit

20. Calculating Average atomic mass
What is the average atomic mass of Lithium?
=0.446
=6.495 (add)

21. Calculating Average atomic mass
What is the average atomic mass of Lithium?
=0.446
=6.495 (add)