4.1 History of the Atom

A. Democritus (Greek model) First to say everything made of atoms atomos – “uncuttable” a means “not” tomos means “cut” Democritus quotes Leucippus: "The atomists hold that splitting stops when it reaches indivisible particles and does not go on infinitely."

Atomic Theory B. Dalton’s model A. All things are made of atoms. They are indivisible and indestructible B. Atoms of the same element are all alike C. Atoms of different elements are different D. Compounds are made from the combination of two or more different atoms

John Dalton

C. Thomson’s Model studied electric current through a gas in a cathode ray tube showed that the charge was negative thought they came from inside the atom

video J.J. Thomson Cathode Ray tube

Problem

Thomson comes up with the Plum Pudding Model

D. Rutherford’s Model

Video Animation

E. Bohr Model Planetary model electrons move about the nucleus of the atom like the planets move about the Sun.

Because Bohr was trying to explain Spectral lines of course !!!!!!!!!! Why the planetary model ? Because Bohr was trying to explain Spectral lines of course !!!!!!!!!! Huh ????? You Know spectral lines !!!!

Bohr’s atom explains only simple atoms like hydrogen Problems with the Bohr Atom Bohr’s atom explains only simple atoms like hydrogen Bohr’s atom does not explain more complex atoms

F. The Wave Model Electrons do not move about the atom in a definite circular pattern. It is impossible to determine the exact location of the electron Heisenburg Uncertainty Principle

Schrödinger's Atom (The wave model) Electrons move in energy levels, they are not just round orbits

4.2 Structure of the Atom

A. Subatomic Particles Protons Neutrons Electrons

Atomic Symbol Mass Number charge Element Symbol Atomic Number

Proton + charge (each proton has a +1 charge) Determines the atomic number Found in the nucleus of the atom (Rutherford)

Electron - charge Determines the charge of the atom Neutral same # protons as #electrons Negative charge more electrons than protons Positive charge fewer electrons than protons Ion – atom where electrons do not equal protons 1 more electron than protons (-1 ion) 2 less electrons than protons (+2 ion)

Neutrons neutral charge Found in the nucleus of the atom

Atomic Number Number of Protons How the periodic table is arranged Hydrogen has 1 proton (atomic number 1) Oxygen has 8 protons (atomic number 8) How the periodic table is arranged

Mass Number Neutrons + Protons 99% of mass in nucleus

Isotopes Same kind of atom (same number of protons) Different number of neutrons