chem 11 - the atom

the historians

Democritus

• first to think about the nature of matter

• broke down pieces of matter until he got down to the essence of the matter

• came up with the name atom; latin for unbreakable

• found out that atoms cannot be created, destroyed or divided

The most powerful people

• king

• church

• both kept “alchemists” who converted metal into gold

Alchemists

• coverting metal into gold didn’t work out; instead they invented most techniques and glassware

John Dalton

• first came up with an experimentally derived model of an atom

• focused on discrete masses of elements (atoms have defined mass) & how they interacted

• made the “Billiard Ball Model”: atoms are smallest particle of matter, indivisible sphere with uniform density

• stated that different elements combine to form compounds

Sir William Crooks

• Cathode Ray Tube (CRT); aka Crooks Tube

  • a primitive vacuum tube(basis for tube TVs) that generates a continuous flow of electrons to create images

  • Proved that cathode rays travel in straight lines and carry energy

• observed negatively charged particles in gas discharge tubes

JJ Thomson

• Proposed the Plum Pudding Model

  • an atom is a sphere of positive charge with negatively charged electrons (plums) within it

  • majority of the mass comes from the protons

• positive and negative balance each other

  • PROTONS: dough

  • ELECTRON: plum

Robert Milikan (milkman)

• Put static charges onto oil droplets

  • the droplets travelled through 2 oppositely charged plates

  • he measured the smallest increment(change) of charge found in the oil droplets

• Discovered the charge of an electron; JJ found out the charge to mass ratio; then he figured out the mass of an electron

Henri Becquerel

• Discovered Radioactivity

• Discovered X-rays emitting from Uranium Salts

Marie Curie

• Discovered the radioactive elements: Radium and Polonium

Ernest Rutherford

• worked on Radioactivity

  • came up with Alpha and Beta radiation

• Gold Foil Experiment

  1. shot alpha particles at a thin sheeet of gold foil

  2. “majority” of the alpha particles passed right through the foil

  3. However, some rebounded off the foil

• discovered the atomic nucleus, and that atom is made up with PROTONS and NUCLEUS

James Chadwick

• Discovered the NEUTRON (inspo of jimmy neutron)

• joined the Manhattan Project and participated in developing the atomic bomb.

Niels Bohr

• Discovered the Bohr Model

• explained the individual spectrum of the elements

  • electrons exist in specific energy states

  • energy that was lost is released as protons of light

• he assumed that electrons are like planets (circling at a defined distance)

• Electrons orbit the nucleus in fixed energy levels (or shells) and can only gain or lose energy by jumping between these levels.

Max Plank

• Proposed the "Quantum Theory”

  • physics of small objects

  • do not behave like large things

• believed that energy was emitted in packets (Quanta) called “photons”

Werner Heisenberg

• contributed to Quantum Mechanics (Atomic Theory)

• came up with Uncertainty Principle

  • it is impossible to know both the position and momentum(speed) of a particle at the same time with precision.

Erwin Schrodinger

• Contributed to Quantum Mechanics

• Described electrons as waves and particles

• Stated that electrons do not orbit

  • Instead there is a cloud where there’s a high “probability” of finding electrons

• In an unenergized atom, the electrons are in a “Ground State” (all electrons as close to the nucleus as possible)

• Quantum Numbers

  • used to describe the quantum (energy levels) where electrons might be found; Cat Thought Experiment