the development of a modern theory of the atom aristotle democritus

The Development of a Modern Theory of the Atom

Aristotle

Democritus

Ancient PhilosophyAristotle

When: More than 2000 years agoWhere: GreeceWhat: Aristotle believed in 4

elements: Earth, Air, Fire, and Water.

The Development of a Modern Theory of the Atom

Democritus (460-370 B.C)• Matter is composed of small, indivisible

particles called atomos.

Ancient Philosophy AND Politics Aristotle rejected Democritus’ ideas –

did not believe that empty space could exist

Aristotle more influential Ideas not science Aristotle’s ideas unchallenged for two

thousand years!!!

John Dalton

The Development of a Modern Theory of the Atom

Dalton (published 1803-1807)

1. All matter is composed of atoms, tiny, indivisible particles of an element that can not be created or destroyed.

Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom

2. Atoms of one element can NOT be converted into atoms of another element. In reactions, atoms of the original substances recombine to form different substances.

Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom

3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element.

Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom

4. Compounds result from chemical combination of a specific ratio of atoms of different elements.

Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom

The Cathode Ray Tube

•Negatively charged particles are present in all matter (later named electrons)

•Cathode Ray Tube Animation

The Cathode Ray Tube

J. J. Thompson

The Development of a Modern Theory of the Atom

Thomson (published 1897)

charge to mass ratio

1.76 x 10-8 C/g

The electrons in an atom balance out the positive,

making it neutral

This can be compared to plums surrounding the

pudding in plum pudding

J.J. Thompson – 1897; England

Thompson credited with discovering electrons

Thompson knew atoms were neutral, but couldn’t find the positive particle.

Robert Millikan

The Development of a Modern Theory of the Atom

Millikan (published 1909) – “Oil Drop Experiment”

charge of electron = 1.60 x 10-19Cmass of electron = 9.10 x 10-28 g

• Millikan's Oil Drop Experiment

The Development of a Modern Theory of the Atom

Millikan•Oil Drop Experiment•Determined charge and mass of electron

The Development of a Modern Theory of the Atom

Rutherford (1871-1937)

The Development of a Modern Theory of the Atom

Rutherford (published 1910)

Rutherford’s Gold Foil Experiment

The Development of a Modern Theory of the Atom

Rutherford (published 1910)

1911- Rutherford’s Atomic Theory

1.Discovery of proton

2.Most of atom is empty space

3.There is a dense nucleus in the middle of every atom with protons surrounded by negative electrons which orbit around the nucleus.

James Chadwick

Discovered neutron!!!

ATOM BASICS

26

Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in

simple ratios to form compounds

27

Subatomic Particles

Particle Symbol Charge RelativeMass

Electron e- 1- 0

Proton p+ + 1

Neutron n 0 1

Atomic Structure

Atoms are composed of 2 regions:

NucleusElectron

Cloud

Atomic Structure

–Nucleus: the center of the atom that contains the mass of the atom

–Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

30

Atomic Number

Number of protons in an atom

All atoms of an element have the same number of protons

31

Atomic Number -Periodic Table

11

Na

Atomic Number

Symbol

32

Atomic Number -Periodic Table

11

Na

11 Protons

Sodium

33

Learning Check

State the number of protons for atoms of each of the following:

Nitrogen

34

Atomic Number -Periodic Table

7

N

7 Protons

Nitrogen

35

Learning Check

State the number of protons for atoms of each of the following:

Sulfur

36

Atomic Number -Periodic Table

16

S

16 Protons

Sulfur

37

Learning Check

State the number of protons for atoms of each of the following:

Barium

38

Atomic Number -Periodic Table

56

Ba

56 Protons

Barium

39

Mass Number

Counts the number of protons and neutrons in an atom

Mass number= p+ + n0

40

Atomic Symbols

Show the mass number and

atomic number

Give the symbol of the

element

41

Atomic Symbols

Na

Mass number

Atomic number

11

23

42

Learning Check

Cl

Mass number

Atomic number

17

35 How many protons?

What is the element?

How many neutrons?

43

Learning Check

Cl

Mass number

Atomic number

17

35

What is the element?

Chlorine

44

Learning Check

Cl

Mass number

Atomic number

17

35 How many protons?

p = atomic # = 17

45

Learning Check

Cl

Mass number

Atomic number

17

35How many neutrons?

n0 = 35 (mass number– 17 (p+)

n0 = 18

46

Number of Electrons

An atom is neutral The net charge is zeroNumber of protons = Number of

electronsAtomic number = Number of

electrons

47

Learning Check

O8

16 n0 =

p+ =

e- =

8

8

8

48

Learning Check

P15

31 n0 =

p+ =

e- =

15

16

15

49

Learning Check

Zn30

65 n0 =

p+ =

e- =

30

35

30

50

IsotopesAtoms with the same number of

protons, but different numbers of

neutrons.

Atoms of the same element (same

atomic number) with different mass

numbers

51

IsotopesIsotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37

LecturePLUS Timberlake 52

Learning Check

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#p _______ _______ _______

#n _______ _______ _______

#e _______ _______ _______

LecturePLUS Timberlake 53

Solution

12C 13C 14C 6 6 6

#p 6 6 6

#n 6 7 8

#e 6 6 6

54

Learning Check

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

B. Number of neutrons in the zinc atom

C. What is the mass number of a zinc isotope

with 37 neutrons? Draw its atomic symbol.

55

Learning Check

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

30

56

Learning Check

An atom of zinc has a mass number of 65.

B. Number of neutrons in the zinc atom

35

57

Learning Check

C. What is the mass number of a zinc isotope

with 37 neutrons? Draw its atomic symbol.

67 Zn30

67

58

Learning Check

Write the atomic symbols for atoms with the following:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

59

Solution

16OA. 8 p+, 8 n, 8 e- 8

B. 17p+, 20n, 17e- 37Cl 17

C. 47p+, 60 n, 47 e- 107Ag 47

60

Atomic Mass on the Periodic Table

11

Na

22.99

Atomic Number

Symbol

Atomic Mass

61

Atomic Mass Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

BEAN BAGIUM

IONIon – charged particle that forms when an atom gains or loses one or more electrons

IONCation – positively charged particle when an atom loses electrons

protons(+) > electrons(-1)

CATION

Ca+2

protons(+) = 20

electrons(-) = 18

IONAnion – negatively charged particle when an atom gains electrons

electrons(-) > protons(+)

CATION

N-3

protons(+) = 7

electrons(-) = 10