Atomic Theory

Question 1

Democritus and Aristotle 420 BCE

Answer 1

Suggested that matter could be broken down into smaller and smaller components and coined “atoms” (invisible)

Question 2

Law of Conservation of Mass

Answer 2

Mass is neither created nor destroyed

Question 3

Law of Definite Proportions

Answer 3

A given compound has the same elements in the same proportions by mass regardless of the size of the sample or the source of the compound

Question 4

Law of Multiple Proportions

Answer 4

If two or more different compounds are composed of the same two elements, then the ratio of their masses is always a ratio of small whole numbers

Question 5

Lavoisier 1789

Answer 5

(Father of modern chemistry) law of conservation of mass

Question 6

Proust 1798

Answer 6

Law of definite proportions

Question 7

Dalton 1804 (law)

Answer 7

Law of multiple proportions

Question 8

Dalton 1810

Answer 8

Published ideas of atomic theory, explaining that atoms were the smallest particles
Also: structure, properties of atoms and compounds, and mass, energy, and volume relationships of atoms

Question 9

Summary of Atomic Theory

Answer 9

All matter is made of atoms, only atoms of the same element are chemically alike, definite, unique average mass of atoms of an element, not subdivided in chemical reactions

Question 10

Empedocles 450 BCE

Answer 10

Avatar elements

Question 11

Electron

Answer 11

Mass=9.1x10^-28 g

Radius=10^-5 angstrom

Question 12

J. J. Thomson 1897

Answer 12

Discovered electrons from flow of electricity using cathode rays

Question 13

Robert Millikan 1909

Answer 13

Additional experiments and mass of electrons

Question 14

Angstrom

Answer 14

SI measure of length; 1 angstrom=10^-10 m

Question 15

Proton

Answer 15

Mass=1.67x10^-24g

Radius is smaller than an electron

Question 16

Eugen Goldstein early 1900s

Answer 16

Positive Ray research led to discovery of proton

Question 17

Ernest Rutherford 1910

Answer 17

Credit for discovering the proton (gold foil experiment)

Question 18

Neutron

Answer 18

Mass=1.67x10^-24g

Radius is smaller than electron

Question 19

James Chadwick 1932

Answer 19

Discovery of neutrons

Question 20

Nucleus Size

Answer 20

10^-4 angstrom, compared to atom size of 1-5 angstrom

Question 21

William Thomson (Lord Kelvin) 1903

Answer 21

Plum pudding model

Question 22

Neils Bohr 1913

Answer 22

Planetary model, then later beehive/electron cloud model

Question 23

AMU

Answer 23

Atomic mass unit, based on carbon-12=12 scale, arbitrary assignment of value

Question 24

Avogadro’s Number

Answer 24

Number of atoms found in one amu of an element, 6.02x10^23 atoms

Question 25

Significant Figures

Answer 25

+ & - : least significant place

X & / : smallest number’s number of sig figs