Exam: History of the Atom Flashcards
Who was Democritus?
-First person to use the term “atom”
-Created the theory of the universe
What did Democritus believe?
That if you take a piece of matter and continuously divide it, you will eventually come to a point where you could not divide it any more
What is an “atom” in Greek?
Fundamental or basic unit
What is Democritus’s Theory of the Universe? (Part 1)
-All matter consists of atoms, which are bits of matter too small to be seen
-There is an empty space between atoms
-Atoms are completely solid
What is Democritus’s Theory of the Universe? (Part 2)
-Atoms have no internal structure
-Each atom of a different substance is different in size, weight, and shape
When did Democritus make his theories?
400 BC
Who was John Dalton?
-Marked the beginning of the atomic theory
-First to adopt Democritus’s theory into the first modern atomic model
When did Dalton make his theories?
1800’s
What is Dalton’s Theory? (Part 1)
-Matter is composed of extremely small particles called atoms
-Atoms are indivisible, indestructible, and unchangeable
-Atoms of a given element are identical in size, mass, and chemical properties
What is Dalton’s Theory? (Part 2)
-Atoms of a specific element are different from those of another element
-Different atoms combine in simple whole number ratios to form compounds
-In a chemical reaction, atoms are separated, combined, or rearranged
Who was J.J. Thomson?
-Credited for discovering the election by using a cathode ray tube
-Used his research on cathode ray tube technology by William Crookes to answer why matter was neutral and what accounts for the rest of the mass in a typical atom
When did J.J. Thomson conduct his work?
1890’s
What happened in the cathode ray tube experiment? (Part 1)
-An eletrical charge is passed through the (nearly) empty tube
-It travels from the cathode to the anode
-It is invisible; only seen on a flourescent screen placed at the back of the tube
-Where the beam hits, a dot will appear on the screen
-Beam will always travel straight
What happened in the cathode ray tube experiment? (Part 2)
-Deflection coils each have a specific charge (one positive, the other negative)
-The charge will deflect away from the negative coil
What was J.J. Thomson able to conclude via his cathode ray tube experiment?
-The mass to charge ratio of the election
-Charge was 1000 times lighter than that of a hydrogen atom
-A negative charge must be inside of an atom;
This was later known as the electron
What was the Plum Pudding Model?
Created by J.J. Thomson;
Describes the atom as negatively charged particles swimming in a positively charged sea
Who was Ernest Rutherford?
Discovered the nucleus by his Gold Foil experiment;
Was not convinced by the model of the atom proposed by Thomson
What happened in the Gold Foil Experiment?
-Positively charged alpha particles were fired at a gold foil
-Rutherford measured the deflection as the particles came out of the other side
-Most of the particles did not deflect at all
-Every now and then, a particle would deflect all the way back
-He concluded there must be a positive center of the foil;
This would later be known as the nucleus
What did Rutherford conclude from his Gold Foil Experiment?
-That there was a positive center to the nucleus
-That the electrons orbited the nucleus
What was the planetary model of the atom?
Created by Rutherford;
Featured the electrons orbiting the nucleus like the planets orbit the sun
What is an isotope?
Atoms of an element that have the same number of protons (an electrons) but a different number of neutrons
