II. History of atomic structure A. Democritus – 500 BCE Theorized that matter is composed of small, indivisible particles = ATOMOS (Greek for indivisible) “Nothing exists except atoms and empty space; everything else is opinion.”

B. Aristotle (Empedocles) – 400 BCE Matter is made up of four elements: Earth, Air, Fire, Water

C. Alchemy – Based on trying to convert base metals into gold They are thought of as the first “scientists”, 1 st “chemists” D.Iatrochemists – 1 st pharmacists Used chemicals to heal illness

E. John Dalton – 1803 Returned to the idea of the atom. 1 st scientist to have observational evidence of small indivisible particles, “atoms”. His model is known as the Solid Sphere Model of the atom Developed an atomic theory based on his observations:

Dalton’s Theory: *Atoms are indivisible particles. *Atoms of the same element are identical. *Atoms of different elements can combine in whole number ratios to form compounds. *Atoms can be separated, joined or rearranged but cannot be turned into another element. Agree/Disagree: *No! Made up of p+, e-, n 0, etc. *No! ISOTOPES and IONS *Yes! H 2 O = 2 hydrogens for every oxygen *True for chemical reactions, not nuclear

F. J.J. Thomson 1897– Discovered electron using Cathode ray tube Applied an electric current that produced a glowing beam that traveled from the cathode (-) to the anode (+).

Came up with Plum Pudding Model: (might be known as chocolate chip model today) The atom is a positive sphere with negative plums embedded in it.

When charged plates (or a magnet) were introduced, the beam was deflected toward the positive plate. Conclusion: *The beam was made up of negatively charged particles moving at high speed. *Called them “corpuscles”, they were later renamed electrons

G. Ernest Rutherford 1911– The Gold Foil Experiment:

Tested the current theory of the atom. Predicted that the alpha particles should have passed easily through the gold foil with a slight deflection due to the positive charge spread throughout the atom.

Observations: The great majority of the particles passed through the foil without deflection. A small fraction bounced off the gold at very large angles. “This is almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”

Rutherford’s Nuclear Atom Model: *The atom is mostly empty space (lack of deflection of particles) *Charge and most of mass concentrated in a small region = nucleus *Enough positive charge in the nucleus to account for large deflection of small number of particles.

H. James Chadwick – 1932 Discovered the neutron 1. The mass of an atom is greater than the combined mass of the p+ and e-. 2. Irene Joliot-Curie bombarded beryllium with alpha particles to produce a beam of particles. 3.Particles making up this beam were similar in mass to a proton but were not deflected by magnetic or electric fields… They are neutral.

III. The electron A. Forces that hold an atom together: 1. STRONG FORCE or NUCLEAR FORCE– Occurs in the nucleus between p + /p +, n 0 /n 0 and p + /n 0 2. ELECTROMAGNETIC – Results from the attraction between oppositely- charged p + and e -.

B. Rutherford - In his description of the atom, he included that e- must be orbiting the nucleus similar to the way the planets orbit the sun. PROBLEMS: 1. Why do elements give off characteristic flame colors when burned? 2. Why do objects glow as heated? Metals: Red  Yellow  White 3. Chemical properties of elements.

C. The Bohr Model – (1913) Niels Bohr 1. Center of the atom is e- orbit the nucleus in a specific path = orbit (Solar System) 3. e- can gain or lose energy to move to a different orbit. QUANTUM = The amount of energy an e- must gain to move to a higher energy orbit. (Rungs of a ladder.) 1 quantum of light energy is known as a PHOTON

D. Louis de Broglie – (1924) Can matter particles behave as waves? Wave-Particle duality 1. Electromagnetic Spectrum:

a. Wavelength (  = lambda) The distance from corresponding points on the same wave. (m, cm) b. Frequency ( = nu) The number of waves that pass a point in a given amount of time. (# of waves /s, s -1, or Hertz = Hz)

Relationship between and : C = C = 3.0 x 10 8 m/s = speed of light As increases, decreases and vice versa

E. Erwin Schrodinger (1926) Theoretical calculations and experimental results did not support Bohr and Rutherford models. QUANTUM MECHANICAL MODEL Or Electron Cloud Model e- are located in a “fuzzy” region known as the e- cloud where the e- are probably located the majority of the time. Based on probable locations, yet no exact location or path predictable.

1. e- cloud is divided into energy levels (like Bohr model), lower energy closer to the nucleus. 2. An electrons exact path is not known, only a mathematical probability of where it should be (Heisenberg Uncertainty principle = never no position and velocity of a particle) 3. Electrons do not exist only in circular locations, there are other varied shapes like a dumbell, clover and others