Atomic Structure

1
Atomic Structure

• Chapter 4

2
Early Theories of Matter

• Greek philosophers (Empedocles 450 B.C.)
• air, water, earth, fire
• Democritos (420 B.C.)
• atoms
• John Dalton (1776-1884)
• All matter made of atoms.
• Atoms of same element are identical vice versa.
• Atoms cannot be created, divided, or destroyed.
• Atoms combine in whole ratios to make
  compounds.
• Atoms are separated, combined, or rearranged in
  chemical reactions.

3
Defining the Atom

• What is an atom?
• Size of atom
• 1 cm 200 000 000 atoms
• Scanning tunneling microscope
• Si atoms on face of a crystal

4
Subatomic Particles

• Discovering the electron
• William Crookes cathode ray tubes
• Stream of charged particles
• Carries a negative charge

5
electron cont

• J.J. Thomson discovered electron (e-)
• mass of e- 9.11 10-28 g
• Plum pudding model (1897)
• Robert Millikan determined charge of electron
• 1.60 10-19 coulombs

6
The Nuclear Atom

• Rutherford discovered nucleus (1911)
• gold foil experiment
• small positive core
• core contains most of atoms mass
• mostly empty space

7
Discovering protons neutrons

• Proton (1919)
• Discovered by Rutherford
• Positively charged in nucleus
• Neutron (1932)
• discovered by Chadwick
• Neutral in nucleus
• Nuclear Model of the Atom

8
Bohr Model of the Atom

• Neils Bohr proposed quantum model of the atom
• Electrons move about the atom in circular paths
  of specific energies
• Termed these paths energy levels
• Later determined to be fundamentally incorrect

9
Quantum Mechanical Model

• Louis de Broglie
• Wave-particle duality
• Erwin Schrödinger
• Electrons treated as waves
• Electrons exist in clouds around the nucleus

10
Summarizing the Atom
11
Summarizing the Atom

• Atoms are electrically neutral (p e-)
• e- held in orbit by attraction to nucleus
• n0 present to break up p repulsion