Chemistry Unit 3 - Atomic

John Dalton

• Law of Partial Pressures

  • Applies to gasses (all gasses)

  • Total pressure of a mixture of gasses is equal to the sum of their partial pressures

    • P1 + P2 + P3 = Pt

    • 2 atm + 3 atm + 6 atm = 11 atm

• Law of Multiple Proportions (review for next test, along with other laws made by other scientists in Unit 2)

• Solid Sphere Model (Dolton’s atom) - 1808

  • Atoms are small, solid, indivisible particles

  • Each element has its own unique atom

  • Atoms of the same element are identical

J.J Thomson

• Cathode Ray Tube experiment

  • Proved that “cathode rays” were small, negatively charged particles that have mass

  • These “cathode rays” are electrons

  • Determined ratio of mass to charge ratio of electrons is 1/1800 of a hydrogen atom

  • Look at the diagram on paper and understand how it works

• Plum Pudding Model - 1897

  • Atoms have pos & neg charges

  • Atom is a positive fluid with negative electrons imbedded throughout (like plums imbedded in pudding, or for a modern example, chocolate chips in a chocolate chip cookie)

  • Atom itself has a negative charge bc the neg cancels out the pos.

Ernest Rutherford

• Found three types of nuclear radiation: Alpha, Beta, Gamma

  • Alpha radiation - positively charged and had mass (meaning it must be a particle)

  • Found out that Nuclear Radiation was the energy + particles from atoms (emitting specific particles from nucleus)

• Gold Foil Experiment

  • Used an alpha emitter to hit a piece of gold foil with particles, found that instead of completely passing through, some deflected (back entirely, or simply in different directions)

  • Helped form the Nuclear Model

• Nuclear Model - 1909

  • Atoms have a small, dense positively charged center

  • Electrons orbit around the nucleus

  • All of the atom’s mass is in the nucleus

  • Atom is mostly empty space (this is why only some particles deflected; Rutherford’s conclusion was that the space was so large that it was unlikely but when they deflected, they must have hit the nucleus)

Niels Bohr

• What his findings found

  • Atoms give off specific wavelengths of light when they are “excited” (electrons have absorbed energy and have jumped to a higher orbital position)

  • Each elements has its own set of spectral lines that are distinct to them and can be used for identification

  • Different wavelengths are emitted from electrons that absorbed energy going back to lower energy state

• Atomic model - Bohr’s Model/Planetary Model

  • Atoms have different energy levels that their electrons orbit instead of a set distance they all orbit at

    • Energy levels work like ladders (energy is not continuous, electrons only stay on the rungs and not the in-betweens)

  • Orbits farther from nucleus are higher energy than those closer

  • Distances vary between atoms - each atom has its own unique distance