Unit 3 Scientists

Dalton

• all matter is made up of atoms

• atoms of one element are identical

• atoms are never created or destroyed

J.J. Thompson

discovery of the electron

• built a device called a cathode ray

• He observed that cathode rays deflected away from negatively charged plates and toward positively charged plates, proving they were negatively charged particles.

Robert Milikan

mass of an electron

• he halted the fall of a charged drop of oil using 2 charged plates

• calculated the charge on the oil drop using the oil volume and mass

• using thompson’s charge to mass ratio he calculated the mass of an electron: 9.11 × 10^-31 kg

Rutherford

nucleus

• discovery: atoms are made of a positively charged center, surrounded by mostly empty space

• he fired alpha particles at gold foil and observed the deflection and passes of the particles through the foil.

James Chadwick

neutron

• worked with Rutherford to discover the neutron

Henri Baquerel, Marie, Pierre Curie

• discovered that certain elements give off radiation

  • alpha a

  • beta B

  • gamma Y

light theory of greek philosophers

light existed a as stream of particles

light theory of Christian Huygens

light existed as a wave

light theory of Isaac Newton

light existed as tiny particles called “corpuscles”

light theory of James Maxwell

light existed as electromagnetic waves in a continuous spectrum

Max Plank

the quantum hypothesis

• matter can gain or lose energy

• on a subatomic level, energy is absorbed or released discontinuously in quanta (small packets of energy)

  • the energies from vibrating atoms were from a multiple of quanta

  • the reason energy appeared to be absorbed and liberated continuously was B/C we were observing many trillions of these events asynchronistically

Hertz

photoelectric effect

• a certain amount of energy is needed from the wavelength of energy to supply for the electrons to be ejected from the metal

Heinsenburg

uncertainty principle

• you cannot know certainly where each electron is.

• if you try to measure an electron, it will change the placement of every other electron

Pauli

exclusion principle

• no 2 electrons can have the exact same 4 quantum numbers in an atom

  • they can have the same n, l, m_l, but spin must be different

Hund’s rule

• electrons occupying an orbital must have parallel spin