1. Describe the shape of an atom using your background knowledge.
Bell Ringer
Describe the shape of an atom using your background knowledge.

3. Topic 9 Charge Behavior and Interactions
© 2014 Pearson Education, Inc.

4. Review Atomic Structure

5. Atomic Structure All matter is composed of atoms.
Understanding the structure of atoms is critical to understanding the properties of matter

6. HISTORY OF THE ATOM ATOMS John Dalton
1808
suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them
ATOMS

7. Subatomic Particles
mass p = mass n = 1840 x mass e-

8. HISTORY OF THE ATOM ELECTRON
Joseph John Thompson
1898
found that atoms could sometimes eject a far smaller negative particle which he called an
ELECTRON

9. A = alpha B = gamma C = beta J.J. Thomson, measured mass/charge of e-
(1906 Nobel Prize in Physics)

10. HISTORY OF THE ATOM
Ernest Rutherford
1910
oversaw Geiger and Marsden carrying out his famous experiment.
they fired Helium nuclei at a piece of gold foil which was only a few atoms thick.
they found that although most of them passed through. About 1 in 10,000 hit

11. Rutherford’s experiment.

12. Density and the Atom
Since most of the particles went through, the atom was mostly empty space.
Because the alpha rays were deflected so much, the positive pieces it was striking were heavy.
Small volume and big mass = big density
This small dense positive area is the nucleus

13. Plum Pudding model of an atom.

14. Results of foil experiment if Plum Pudding model had been correct.

15. Actual Results.

16. A nuclear atom viewed in cross section.

17. Rutherford’s Model of the Atom
atomic radius ~ 100 pm = 1 x m
nuclear radius ~ 5 x 10-3 pm = 5 x m

18. HISTORY OF THE ATOM Niels Bohr 1913
studied under Rutherford at the Victoria University in Manchester.
Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.

19. n (principal quantum number) = 1,2,3,…
Bohr’s Model of
the Atom (1913)
e- can have only specific (quantized) energy values
light is emitted as e- moves from one energy level to a lower energy level
En = -RH
( ) 1 n2
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J

20. Atomic Structure Atoms are composed of
-protons – positively charged particles
-neutrons – neutral particles
-electrons – negatively charged particles
Protons and neutrons are located in the nucleus. Electrons are found in orbitals surrounding the nucleus.

21. HELIUM ATOM
Shell
proton N + - + N -
neutron
electron

22. Atomic Structure
Every different atom has a characteristic number of protons in the nucleus.
atomic number = number of protons
Atoms with the same atomic number have the same chemical properties and belong to the same element.

23. number of electrons = number of protons
ATOMIC STRUCTURE He
Atomic number 2
the number of protons in an atom 4
Atomic mass
the number of protons and
neutrons in an atom
number of electrons = number of protons