History of Atom Theory (Ch 2) Flashcards
1
Q
Democritus
A
- Went against Aristotle, who believed that matter was composed of four qualities: earth, fire, air, and water
- All matter is composed of small, invisible particles
- Coined the term “atomos” (meaning indivisible)
2
Q
Law of conservation of mass
A
- Lavoisier
- Mass is neither created nor destroyed in a chemical reaction
- Ex: 2 g H + 16 g O = 18 g water
3
Q
Law of definite proportions (constant composition)
A
- Proust
- Elements combine in definite, fixed ratios by mass to form compounds
- Ex: water is always 1 gram of hydrogen for 8 grams of oxygen
4
Q
John Dalton
A
- Developed a model on the atom based on already established laws:
- Law of conservation of mass
- Law of definite proportions
- Law of multiple proportions
5
Q
Law of multiple proportions
A
- Dalton
6
Q
Dalton’s Atomic Theory
A
- All matter is made up of extremely small particles called atoms (TRUE)
- Atoms of a given element are identical in size, mass, and other properties (diff elements differ in properties) (FALSE)
- Atoms cannot be subdivided, created, or destroyed (FALSE)
- Atoms of different elements can combine in fixed, small, whole-number ratios to form compounds (TRUE)
- Chemical reactions involve the combining, separating, or rearrangement of atoms to form new substances (TRUE)
Model of atom: cannonball model
7
Q
Sir William Crookes
A
- 3 experiments to look at the nature of cathode rays:
- Used a magnet to determine that the ray has charge -
- Used a Maltese Cross to determine that the ray moves in a straight line/path
- Used a paddle wheel to determine that the ray has mass (beam can transfer momentum)
8
Q
Sir J J Thomson
A
- Hypothesis: since the beam came from the cathode (a negative electrode), and given how the ray is deflected by a magnet, the particles have a negative charge
- CRT
- Plum pudding mode
9
Q
CRT
A
- Sir J J Thomson
- Tried to separate the charge from the particles by bending the rays with a magnet and then deflecting with electric plates
- He could not separate the two
- Calculated the charge to mass ratio of these particles by measuring the degree of deflection with different strength magnetic / electric fields
- No matter which gas he used in the tube, the calculated charge to mass ratio was the same (1/1800 of a H atom)
- Convincing evidence that the rays consisted of charged particles
- Nobel Prize 1906 - discovery of the electron
10
Q
Plum Pudding Model
A
- Thomson
- Cathode ray made up of negatively charged subatomic particles (later called electrons)
- No matter what metal electrodes made of or what gas filled the tube, the same charge to mass ratio was calculated (all atoms have them, identical in all atoms)
- Atoms must also have positive component - ball of positive charge with negative charges spread throughout, like raisins in plum pudding
11
Q
Oil Drop Experiment
A
- Millikan
- Determined the charge of an electron
- Given Thomson’s charge to mass ratio calculation, the mass of an electron could then also be determined
- Oil drops given in negative charge by attaching electrons to them
- Balance force of gravity with force from electric field on those droplets
- Could determine magnitude of charge on each oil drop, found that charge was multiple of 1.6 x 10-19 C
- Therefore single electron 1.6 x 10-19 C
12
Q
Radioactivity
A
- The spontaneous disintegration of some elements into smaller pieces
- Term coined by Marie Curie
13
Q
Types of radioactive emissions
A
- Alpha - can’t penetrate through paper
- Beta
- Gamma - pure light/energy
14
Q
Earnest Rutherford
A
- Responsible for the modern, nuclear view of the atom
15
Q
Gold Foil Experiment
A
- Earnest Rutherford
- Trying to prove plum pudding model - if supported the alpha particles would all pass straight through foil
- Most passed straight through, some slightly deflected
- Some completely deflected
-
Conclusions:
- Majority of atom empty space
- Positive charge + 99% of atom’s mass concentrated in small volume in center (discovery of nucleus)
- Electrons orbit around nucleus (much smaller mass)
