The Structure of the Atom

1
Chapter 4

• The Structure of the Atom

2
Chapter 4

• Section 1
• Early Ideas About Matter

3
Back in the day. . . Way back

• Science
• Did not always exist as it does now
• Curiosity
• Sparked the interest of philosophers
• Philosophersgreat thinkers
• Considered many mysteries of life

4
Greek Philosophers

• Nature of Matter
• Formulated explanations based on their own life
  experiences
• Many Concluded
• Matter was made of four things
• Earth
• Water
• Air
• Fire

5
Greek Philosophers

• Commonly Accepted
• Fire, Earth, Air, and Water could be broken down
  into smaller and smaller pieces
• Creative Ideas
• No way to test their validity

6
Democritus

• 460-370 B.C.
• First person to propose that matter was NOT
  infinitely divisible
• He believed
• Atomos
• Tiny particles that make up matter
• Where the English word Atom comes from

7
Democritus

• Also believed
• Atoms could not be
• Created
• Destroyed
• Or further divided
• Different kinds of atoms have different sizes and
  shapes
• Size, shape, and movement of atoms determine
  properties of matter

8
Aristotle

• 384-322 B.C.
• Rejected notion of atoms
• Empty space cannot exist
• Matter is made of Earth, Fire, Water, Air
• Popular and widespread
• Unchallenged for about 2000 years

9
John Dalton

• 1766-1844
• School teacher in England
• Began the development of modern atomic theory
• Revived Democrituss ideas

10
John Dalton

• Daltons Atomic Theory
• Matter is composed of extremely small particles
  called atoms
• Atoms are indivisible and indestructible
• Atoms of a given element are identical in size,
  mass, and chemical properties
• Atoms of a specific element are different from
  those of another element

11
John Dalton

• Daltons Atomic Theory continued
• Different atoms combine in simple whole-number
  ratios to form compounds
• In a chemical reaction, atoms are separated,
  combined or rearranged

12
Conservation of Mass

• Law of Conservation of Mass
• Within a chemical reaction, the mass of the
  products is the same as the mass of the reactants.

Products
Reactants
13
Section 2

• Defining the Atom

14
The Atom

• the smallest particle of an element that retains
  the properties of the element
• Imagine making an atom the size of an orange
• An orange would become the size of the earth
• Can be seen using STM
• Scanning Tunneling Microscope

15
The Electron

• The Cathode-ray tube
• Scientists began to make connections between
  matter and electrical charge
• Typical cathode-ray tube consists of
• Cathode
• Anode
• Metal electrodes

16
Sir William Crookes

• English physicist
• Cathode ray
• Light traveling from the cathode to the anode
• Led to the invention of the television

17
Cathode Ray Tube
18
By the end of the 1800s

• Scientists were fairly convinced that
• Cathode rays were a stream of charged particles
• The particles carried a negative charge
• Exact value of negative charge was unknown
• Electron
• Negatively charged particles that are part of all
  forms of matter

19
Mass and Charge of Electron

• J.J. Thompson (1856-1940)
• Series of cathode ray experiments
• Cambridge University
• Late 1890s
• Determined Charge to Mass Ratio
• me

20
Mass and Charge of Electron

• J.J. Thompson
• Determined Charge to Mass Ratio
• Measured the effects of both magnetic and
  electric fields of a cathode ray
• Compared this ration to other known ratios
• Concluded that the mass of the charged particle
  was much less than that of a hydrogen atom
• Shocking! Particles smaller than an atom!

21
Mass and Charge of Electron

• J.J. Thompson
• Received Nobel Prize in 1906
• Discovered the first sub-atomic particle
• The electron
• Other scientists found this hard to accept

22
Oil Drop

• Early 1910s
• Robert Millikan
• (1868-1953)
• Determined charge of an electron
• Used oil drop experiment
• Charge 1.602 x 10-19 coloumbs
• Charge 1-

23
The Plum Pudding Model

• Matter is neutral
• No electrical charge
• J.J. Thompson proposed a model
• Plum Pudding Model

24
Plum Pudding Model
25
The Nucleus

• 1911
• Ernest Rutherford (1871-1937)
• Began to study how positively charged alpha
  particles interacted with solid matter
• Conducted an experiment to see if alpha particles
  would be deflected as they passed through a thin
  gold foil

26
Rutherfords Experiment
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Rutherfords Experiment

• Narrow beam of alpha particles
• Thin sheet of gold foil
• Zinc-sulfide coated screen produced a light when
  hit with an alpha particle
• Noting where the flashes occurred allowed
  scientists to determine if atoms in the gold
  deflected alpha particles

28
Rutherfords Experiment

• Rutherford knew of Thompsons model
• Expected
• Paths of the massive fast moving alpha particles
  to be only slightly altered by a collision with
  an electron
• Positive charge evenly distributed, not alter
  paths of alpha particles

29
Rutherfords Experiment

• Actual results
• A few of the alpha particles were deflected at
  large angles
• Several were deflected straight back

30
Rutherfords Model

• Concluded Plum Pudding/Ritas water ice model is
  incorrect
• Most of the positive charge and almost all of its
  mass were contained in a tiny dense region in the
  center
• Nucleus
• Incredibly dense
• Atoms diameter is 10,000 times the diameter of
  the nucleus

31
The proton and the neutron

• By 1920
• Rutherford refined the concept of the nucleus
• Concluded that the nucleus contained positively
  charged particles
• Protons
• A subatomic particle carrying a charge equal to
  but opposite that of an electron 1

32
The proton and the neutron

• In 1932
• English physicist James Chadwick (1891-1974)
• Nucleus also contains another subatomic particle
• Neutron
• a subatomic particle that has a mass nearly
  equal to that of a proton, but it carries no
  electric charge
• Received Nobel Prize in Physics, 1935

33
Completing the Model of the Atom

• All atoms are made up of three fundamental
  subatomic particles
• Electron
• Proton
• Neutron
• Atoms are spherically shaped
• Atoms have a small dense nucleus of positive
  charge surrounded by one or more negatively
  charged electrons

34
Completing the Model of the Atom

• Most of an atom consists of fast-moving electrons
• Electrons held within the atom by their
  attraction to the nucleus
• Nucleus made of positive and neutrally charged
  particles
• Proton and Neutron

35
Basic atomic structure
36
Subatomic particles

• Research in this area is still a major interest
  to modern scientists
• Protons and neutrons have their own structure
• Composed of subatomic particles called quarks

37
Section 3

• How Atoms Differ

38
Atomic Number

• Henry Moseley (1887-1915)
• Discovered that atoms of each element contain a
  unique positive charge in their nuclei
• The number of protons in an atom identifies it as
  an atom of a particular element
• The number of protons in an atom

39
Atomic Number

• The periodic table is organized from
  left-to-right and top-to-bottom by increasing
  atomic number
• Hydrogen has the atomic number of 1
• Has 1 proton

40
Atomic Number

• All atoms are neutral
• The number of protons number of electrons
• Atomic number tells you
• Number of protons
• Number of electrons

41
Homework

• Identify the atomic number, number of protons,
  and/or number of electrons of the following
• Helium
• 72 protons
• 111 electrons
• Palladium
• Atomic 52

42
Isotopes and Mass Number

• Dalton stated that
• Atoms are indivisible
• Atoms of an element are identical
• Dalton was wrong!
• All atoms of an element have
• Same of protons
• Same of electrons
• Neutrons can vary!

43
Isotopes and Mass Number

• For example Potassium
• There are three atoms that occur naturally
• All three contain
• Same of protons
• Same of electrons
• As for neutrons
• One has 20
• One has 21
• One has 22

44
Isotopes and Mass Number

• Isotopes
• Atoms with the same of protons, but different
  of neutrons

45
Mass of Isotopes

• Isotopes containing more neutrons
• Have greater mass
• Isotopes of an atom
• Have same chemical behavior
• Chemical behavior determined by electrons

46
Isotope Notation

• Each isotope of an element is identified with a
  mass number
• Mass Number
• The sum of the atomic number/number of protons
  and neutrons in nucleus
• and N Mass

47
Isotope Notation

• Example Copper
• Has 2 isotopes
• Isotope with 29 protons, 34 neutrons has a mass
  of 63
• Known as Copper-63
• Cu-63 63Cu
• Isotope with 29 protons, 36 neutrons has a mass
  of 65
• Known as Copper-65
• Cu-65 65Cu

48
Natural Abundance of Isotopes

• Most elements are found as mixture of isotopes
• Relative abundance tends to be constant
• Example Potassium in Bananas
• 93.26 of K atoms have 20 neutrons
• 6.73 of K atoms have 22 neutrons
• 0.01 of K atoms have 21 neutrons

49
Mass of Atoms

• Atomic Mass Unit
• Amu
• Used b/c extremely small masses in scientific
  notation are hard to work with
• Atomic Mass Unit
• Defined as one-twelfth the mass of a carbon-12
  atom

50
Atomic Mass Unit

• Mass of 1 amu
• Nearly mass of a p or N
• Values are different
• e- 0.000549 amu
• p 1.007276 amu
• N 1.008665 amu

51
Atomic Mass

• The weighted average mass of the isotopes of that
  element

52
Problems Part 1Atomic Mass and Atomic Number

• Find the number of protons for the following
  elements
• Carbon
• Oxygen
• Europium
• Palladium
• Molybdenum
• Nitrogen
• Helium

53
Problems Part 2

• Find the number of electrons for the following
• Tin
• Potassium
• Calcium
• Gold
• Mercury
• Gallium
• Silicon
• Boron
• Lithium

54
Chapter 4

• Section 4

55
Reactions

• Reaction Types
• Chemical and Nuclear
• Chemical reaction
• The change of one or more substances into new
  substances
• Involves only an atoms electrons
• Atoms may be rearranged
• Identity remains the same

56
Nuclear Reactions

• Nuclear Reactions
• Can change an element into a new element
• A reaction that involves a change in an atoms
  nucleus
• Radioactivity
• Late 1890s
• Substances spontaneously emitted radiation
• Radioactivity is the name given to this process

57
Nuclear Reactions

• Scientists discovered
• Radioactive atoms undergo changes
• Changes can alter atoms identities
• Major Breakthrough
• Reaction that involves atoms becoming new atoms
• Radioactive atoms emit radiation, b/c nuclei are
  unstable

58
Radioactive Decay

• Radioactive Decay
• Unstable nuclei lose energy by emitting radiation
  in a spontaneous process
• Unstable atoms
• Undergo radioactive decay until they form stable
  atoms
• Often different elements

59
Types of Radiation

• Late 1800s
• Scientists began researching radioactivity
• They investigated
• The effect of electric fields on radiation
• Radiation either deflected towards the
• Negative plate
• Positive plate
• Not at all
• Identified three different types

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Types of Radiation

• Alpha
• a
• Beta
• ß
• Gamma
• ?

61
Negative
?
a
ß
Positive
62
Alpha Radiation

• Alpha Radiation
• Radiation that was deflected towards negatively
  charged plate
• Made of alpha particles
• Alpha Particle
• Contains 2 protons and 2 neutrons
• Has 2 charge

63
Negative
?
a
ß
Positive
64
Beta Radiation

• Beta Radiation
• Radiation that was deflected toward the positive
  charged plate
• Consists of fast moving beta-particles
• Beta Particle
• An electron with a 1- charge
• ß
• e-

65
Negative
?
a
ß
Positive
66
Gamma Radiation

• Gamma Radiation
• Radiation that was not deflected
• Also called Gamma Rays
• Gamma Ray
• A high energy radiation that possesses no mass
• ?

67
Negative
?
a
ß
Positive