Exam: History of the Atom

Question 1

Who was Democritus?

Answer 1

-First person to use the term “atom”
-Created the theory of the universe

Question 2

What did Democritus believe?

Answer 2

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

Question 3

What is an “atom” in Greek?

Answer 3

Fundamental or basic unit

Question 4

What is Democritus’s Theory of the Universe? (Part 1)

Answer 4

-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

Question 5

What is Democritus’s Theory of the Universe? (Part 2)

Answer 5

-Atoms have no internal structure
-Each atom of a different substance is different in size, weight, and shape

Question 6

When did Democritus make his theories?

Answer 6

400 BC

Question 7

Who was John Dalton?

Answer 7

-Marked the beginning of the atomic theory
-First to adopt Democritus’s theory into the first modern atomic model

Question 8

When did Dalton make his theories?

Answer 8

1800’s

Question 9

What is Dalton’s Theory? (Part 1)

Answer 9

-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

Question 10

What is Dalton’s Theory? (Part 2)

Answer 10

-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

Question 11

Who was J.J. Thomson?

Answer 11

-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

Question 12

When did J.J. Thomson conduct his work?

Answer 12

1890’s

Question 13

What happened in the cathode ray tube experiment? (Part 1)

Answer 13

-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

Question 14

What happened in the cathode ray tube experiment? (Part 2)

Answer 14

-Deflection coils each have a specific charge (one positive, the other negative)
-The charge will deflect away from the negative coil

Question 15

What was J.J. Thomson able to conclude via his cathode ray tube experiment?

Answer 15

-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

Question 16

What was the Plum Pudding Model?

Answer 16

Created by J.J. Thomson;
Describes the atom as negatively charged particles swimming in a positively charged sea

Question 17

Who was Ernest Rutherford?

Answer 17

Discovered the nucleus by his Gold Foil experiment;
Was not convinced by the model of the atom proposed by Thomson

Question 18

What happened in the Gold Foil Experiment?

Answer 18

-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

Question 19

What did Rutherford conclude from his Gold Foil Experiment?

Answer 19

-That there was a positive center to the nucleus
-That the electrons orbited the nucleus

Question 20

What was the planetary model of the atom?

Answer 20

Created by Rutherford;
Featured the electrons orbiting the nucleus like the planets orbit the sun

Question 21

What is an isotope?

Answer 21

Atoms of an element that have the same number of protons (an electrons) but a different number of neutrons