Chapter 4 Atomic History

Question 1

Aristotle c.420 BCE

Answer 1

• decides that there are four base elements: earth, air, fire, and water
• Greek philosopher

Question 2

Democritus c. 400 BCE

Answer 2

-creates concept of “atomos” (atom), an indivisible and indestructible unit of matter

Question 3

John Dalton 1808

Answer 3

• heavy hitter in sciences
• creates Atomic Theory, periodic table w/ 32 elements, the Law of Definite Proportions
• his idea of atom looked like a solid sphere

Question 4

John Dalton’s Atomic Theory

Answer 4

1. all elements are composed of atoms (credit: Democritus)
2. all atoms of same element are identical (mostly true, today we know of isotopes)
3. Atoms of different elements combine in ratios of whole #s
4. In chemical reactions, atoms can rearrange themselves (credit: Lavoisier!!!)

Question 5

Antoine Lavoisier 1760s

Answer 5

‘father of modern chemistry’

• made chemistry science of MEASUREMENT
• proved oxygen needed to burn
• matter is neither created nor destroyed in chemical reactions (see 4th principle of atomic theory)

Question 6

Law of Definite Proportions

Answer 6

Atoms of different elements combine in ratios of whole #s , those ratios define what substance it is (ex: 2 Hydrogens one Oxygen means water)

Question 7

Henri Bequel 1896

Answer 7

employs Pierre and Marie Curie
DISCOVERS radioactivity through camera film accident
they know energy is being given off (in particles)
discover three types of particles
-alpha
-beta
-gamma

Question 8

3 Radioactive Particles

Answer 8

Alpha:
big, non-penetrating
Beta:
small, penetrate
Gamma:
pure energy

Question 9

JJ Thompson 1903

Answer 9

discovers electron using cathode ray

Question 10

cathode ray

Answer 10

tube with negative and positive ends, electrically charged
beam of light sent from negative to positive side
(in Thompson’s experiment: he adds negative and positive fields throughout, beam gets diverted to the positive charges, thompson concludes atom is negatively charged a.k.a discovers electron)

Question 11

Plum Pudding Model

Answer 11

model of atom created by JJ Thompson, consists of soild sphere with RANDOM negative charges throughout

Question 12

Albert Einstein

Answer 12

wins 1st Nobel Prize arguing that we can CONTROL electrons (by getting them to be given off through charges/light beams)
begins new era of electrons as the thing to experiment with

Question 13

Ernest Rutherford 1909

Answer 13

uses GOLD FOIL experiment to test Plum Pudding Model
(beam particles should go straight through, but don’t, some deflect, etc.)
determines:
-atoms mostly empty space (credit: Democritus)
-dense, positive charged mass in atom (a.k.a nucleus)
-creates planetary model

Question 14

gold foil experiment

Answer 14

gold (bendable and dense) is pressed into thin thin foil and laid in center of ring of phosphorous-coated screen (glows when struck). light is beamed through block of led to gold. particles are deflected off (Some go through)

results: like seeing bullet bounce off of lace; proves that some atomic particles are positive (bouncing off of positive gold)

Question 15

Planetary Model

Answer 15

• created by Rutherford
• e- orbiting + nucleus in a ring
• however, didn’t explain why neg and positive didn’t crash into each other, or for interaction between electrons