History of Atom / Atomic Structure

Question 1

What were Democritus’s Earliest Ideas About the Atom?

Answer 1

• Atoms were indivisible; couldn’t be cut.
• Smallest Particle of an Element & Holds Chem. Identity of the Element

Question 2

What is Dalton’s Atomic Theory?

Answer 2

• Matter is composed of tiny particles: Atoms.
• Atoms are indestructible; rearranged, but never broken apart.
• Wrong: Can be broken into proton, neutrons, & electrons.
• Atoms of a given element are identical in mass, size, & chemical properties.
• Wrong: Atom’s have different isotopes, which can lead them to weigh differently.
• Atoms of one element are different from those of another
• Different atoms combine in simple, whole number ratios to form compounds.

Question 3

J.J Thompson

Answer 3

Experiment: Used a Cathode Ray Tube & discovered - particles were migrating from - magnetic field.
Conclusion: Discovered electrons; Atoms were composed of - particles.

Question 4

Ernest Ruthford

Answer 4

Experiment: Shot Alpha Particles from Uranium into a gold sheet; Found certain particles were deflecting.
Conclusion: Atoms are mostly empty space, however, they have a dense, positively charged center (Nucleus)

Question 5

Robert Andrews Millikan

Answer 5

Experiment: Sprayed oil into a container which held a + Plate & - Plate
Conclusion: Determined an e- charge was = 1.9 x 10-19 coulombs

Question 6

Differences: Billiard Ball V. Plum Pudding V. Nuclear Models of an Atom

Answer 6

Billiard Ball: Atoms were like a pool ball; Tiny, dense, & indivisible.
Plum Pudding: Atoms had tiny, - particles in the center & + shell; Overall atom had no charge.
Nuclear Model: Electrons lived outside the Nucleus, whereas Protons & Neutrons lived inside of it.