The Atom Chapter 4 Flashcard

Democritus
Matter is not infinitely divisible
Discontinuous theory of matter
Atoms move in empty space
No experiments to support the idea
Aristotle
Disagreed with Democritus and “empty space”
Continuous theory of matter
Did not have proof
Alchemy
Pseudoscience
Obsessed with turning cheap metals into gold
Some were serious
John Dalton
Beginning of modern atomic theory
Used experiments for his theory
Law of Conservation of Mass
Confirmed by Lavoisier
Matter is not created nor destroyed
Law of Definite Proportions
A compound contains the same elements in exactly the same proportions by mass (no matter the amound present or the source)
Law of Multiple Proportions
Formulated by Dalton
When two elements form a series of compounds,the ratios of the masses can always be reduced to a whole number.
Dalton’s Atomic Theory
All matter is composed of atoms
All atoms of an element are identical
Atoms cannot be created or destroyed
Different atoms combine in whole number ratios
Atoms or one element are never changed into atoms of another element
William Crookes
Worked with evacuated glass tube
Noticed flash of light
Discovered cathode ray tube
J.J. Thomson
Crooke’s student.
Thomson believed cathode waves consisted of some type of particle
Plum Pudding Model- cookie dough
Thomson’s Experiment
Passed an electric current that moved from negative to positive end.
Added another field and found moving pieces to be negative.
Used different metals and gases, but got same results
ALL atoms must contain negative particles
Robert Millikan
Suspended an oil drop between two plates
Calculated the charge and mass on a single electron
Ernest Rutherford
Studied under Thomson
Noticed ‘alpha’ particles being deflected
Gold-foil experiment
Explain the Gold-foil Experiment
-Lead block contains Uranium. Shot alpha particles through this into gold foil.
-Paticles should have continued through
-Some paticles deflected
-Particles were hitting something positive that was small, but incredibly dense
Results of Gold-foil Experiment
There was a positive particle in teh atom- proton
Came up with the nuclear model of the atom.
What are the two regions of the atom?
The Nucleus- Protons and Neutrons, + charge, almost all the mass
Electron Cloud- most of the volume of an atom, electrons
Size of an Atom
tiny
Nucleus is dense
Atomic Number
Number of protons-determines kind of atom
On periodic table
Number of electrons in a neutral atom
Mass Number
Number of protons plus the neutrons
Always a whole number
NOT on the Periodic Table
Isotopes
Dalton was wrong- atoms of the same element can have different numbers of neutrons
-carbon-12 (mass number after element)
Atomic Mass
On the Periodic Table
Based on % abundance in nature
Called Atomic Weight
(amu)
Each isotope had different atomic mass

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