1. Atomic Theory

2. 4.1
Atomic Theory

3. Atomic Theory
theory: an explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true

4. Atomic Theory
Dalton's atomic theory
The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's.

5. Greek Philosophers
Many ancient scholars believed matter was composed of such things as earth, water, air, and fire.
Many believed matter
could be endlessly divided
into smaller and smaller
pieces.

6. Greek Philosophers
Democritus (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos.
Aristotle (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist.
Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas.

7. Democritus Came up with idea of the atom.
Greek philosopher B.C.
Came up with idea of the atom.
Used logical thinking - No experimentation.
Atomos = Greek for 'indivisible'.
Everything in the universe is made up of atoms – microscopic, indestructible, solid spheres.
Constantly in motion and can combine in different combinations.

8. Greek Philosophers

9. Dalton
John Dalton revived the idea of the atom in the early 1800s based on numerous chemical reactions. (experiment based!)
Dalton’s atomic theory easily explained conservation of mass in a reaction as the result of the combination, separation, or rearrangement of atoms.

10. Dalton

11. John Dalton Father of the Atom First Atomic Theory stated:
Each element composed of atoms.
Atoms of an element are identical
Different element’s atoms have different characteristics.
Atoms combine in whole # ratios to form compounds.
Chemical reactions occur due to separating and rejoining or rearranging of atoms.
Atoms of 1 element can’t change into another element.

12. 4.1 Check
Who was the first person to propose the idea that matter was not infinitely divisible?
A. Aristotle
B. Plato
C. Dalton
D. Democritus

13. 4.1 Check Dalton’s theory also conveniently explained what?
A. the electron
B. the nucleus
C. law of conservation of mass
D. law of Democritus

14. Subatomic particles and the nuclear atom
4.2
Subatomic particles and the nuclear atom

15. 4.2 Review Vocabulary
model: a visual, verbal, and/or mathematical explanation of data collected from many experiments

16. 4.2 New Vocabulary atom cathode ray electron
nucleus
proton
neutron
Main Idea - An atom is made of a nucleus containing protons and neutrons; electrons move around the nucleus.

17. 4.2 The Atom
The smallest particle of an element that retains the properties of the element is called an atom
An instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen.

18. J. J. Thomson Identified the electron and proton.
British scientist ( )
Identified the electron and proton.
Discovered electrons using the cathode ray tube and magnets.
Concluded that the electron was negatively charged and the proton positively charged.
“Plum Pudding” model: Positive sphere with negative electrons embedded in it. (Like chocolate chip cookie dough)

19. 4.2 The Electron
When an electric charge is applied, a ray of radiation travels from the cathode to the anode, called a cathode ray.
Cathode rays are a stream of particles carrying a negative charge.
The particles carrying a negative charge are known as electrons.

20. 4.2 The Electron
This figure shows a typical cathode ray tube.

21. 4.2 The Electron

22. 4.2 The Electron

23. 4.2 The Electron
J.J. Thomson measured the effects of both magnetic and electric fields on the cathode ray to determine the charge-to-mass ratio of a charged particle, then compared it to known values.
The mass of the charged particle was much less than a hydrogen atom, then the lightest known atom.
Thomson received the Nobel Prize in 1906 for identifying the first subatomic particle—the electron

24. 4.2 The Electron
In the early 1910s, Robert Millikan used the oil-drop apparatus shown below to determine the charge of an electron.

25. Mass of the Electron
Mass of the electron is
9.11 x g
The oil drop apparatus
1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge

26. 4.2 Conclusions about The Electron
Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.
Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons
Electrons have so little mass that atoms must contain other particles that account for most of the mass

27. the mass of a hydrogen atom
4.2 The Electron
Charges change in discrete amounts—1.602  10–19 coulombs, the charge of one electron (now equated to a single unit, 1–).
With the electron’s charge and charge-to-mass ratio known, Millikan calculated the mass of a single electron.
the mass of a hydrogen atom

28. 4.2 The Electron Matter is neutral.
J.J. Thomson's plum pudding model of the atom states that the atom is a uniform, positively changed sphere containing electrons.

29. Ernest Rutherford Discovered the nucleus.
Experimented using alpha radiation and gold foil.
Nucleus is a dense, positive core in the center of the atom
Electrons move around the nucleus.
Atom is mostly empty space.
nucleus

30. James Chadwick Identified the neutron. Neutron has no charge.
Found in nucleus.
Has a mass greater than a proton.
Neutron served as “nuclear cement” by separating the protons and accounted for missing mass of atom.

31. 4.2 The Nucleus
In 1911, Ernest Rutherford studied how positively charged alpha particles (helium nuclei) interacted with solid matter.
By aiming the particles at
a thin sheet of gold foil,
Rutherford expected the
paths of the alpha particles
to be only slightly altered by
a collision with an electron.

32. 4.2 The Nucleus
Although most of the alpha particles went through the gold foil, a few of them bounced back, some at large angles.

33. 4.2 The Nucleus
Rutherford concluded that atoms are mostly empty space.
Almost all of the atom's positive charge and almost all of its mass is contained in a dense region in the center of the atom called the nucleus.
Electrons are held within the atom by their attraction to the positively charged nucleus.

34. 4.2 The Nucleus
The repulsive force between the positively charged nucleus and positive alpha particles caused the deflections.

35. 4.2 The Nucleus
Rutherford refined the model to include positively charged particles in the nucleus called protons.
James Chadwick received the Nobel Prize in 1935 for discovering the existence of neutrons, neutral particles in the nucleus which accounts for the remainder of an atom’s mass.

36. 4.2 The Nucleus
All atoms are made of three fundamental subatomic particles: the electron, the proton, and the neutron
Atoms are spherically shaped.
Atoms are mostly empty space, and electrons travel around the nucleus held by an attraction to the positively charged nucleus.

37. 4.2 Subatomic Particles

38. 4.2 Subatomic Particles
Scientists have determined that protons and neutrons are composed of subatomic particles called quarks.
Chemical behavior can be explained by considering only an atom's electrons.

39. Neils Bohr Developed the Bohr Model of the atom.
Bohr Model: Electrons move around the nucleus in fixed, circular orbitals that have a set amount of energy levels.
Racetrack model

40. Erwin Schrödinger Inventor of the theory of quantum mechanics
Described the electron as a wave function rather than as a particle
Assigned 4 quantum numbers to an electron in an atom to describe its location (s, p, d, f)
Electrons in ‘clouds’

41.      Summary
Greeks (Democritus) BC matter was made of tiny particles elements: earth, wind, fire, water John Dalton  (Father of the Atom)   early 1800's            matter is made of indivisible particles called atoms            all atoms of same element are alike
J.J. Thomson   1897           discovered electron with negative charge; reasoned the existence of positive particle           plum pudding model
Ernest Rutherford             discovered nucleus containing positive particles           gold foil experiment Neils Bohr   1913           energy levels holding electrons           worked with Rutherford and Einstein Erwin Schrödinger   1926           Electrons in clouds           Quantum (wave) theory           Assigned a set of four quantum numbers to describe the location of an electron
James Chadwick             discovered neutron           neutron holds protons apart           explained mystery of mass and 'glue' to hold nucleus together

42. 4.2 Check Atoms are mostly ____. A. positive B. negative
C. solid spheres
D. empty space

43. 4.2 Check
What are the two fundamental subatomic particles found in the nucleus?
A. proton and electron
B. proton and neutron
C. neutron and electron
D. neutron and positron

44. 4.3
How atoms differ

45. 4.3 How Atoms Differ Review Vocabulary
periodic table: a chart that organizes all known elements into a grid of horizontal rows (periods) and vertical columns (groups or families) arranged by increasing atomic number

46. 4.3 How Atoms Differ New Vocabulary
atomic number
isotopes
mass number
atomic mass unit (amu)
atomic mass
Main Idea - The number of protons and the mass number define the type of atom.

47. 4.3 Atomic Number
Each element contains a unique positive charge in their nucleus.
The number of protons in the nucleus of an atom identifies the element and is known as the element’s atomic number.

48. 4.3 Atomic Number
Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.

49. 4.3 Isotopes and Mass Number
Dalton was wrong about all elements of the same type being identical.
Atoms of the same element can have different numbers of neutrons.
Thus, different mass numbers.
These are called isotopes.

50. 4.3 Isotopes and Mass Number
All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ.
Atoms with the same number of protons but different numbers of neutrons are called isotopes.

51. 4.3 Isotopes and Mass Number
The relative abundance of each isotope is usually constant.
Isotopes containing more neutrons have a greater mass.
Isotopes have the same chemical behavior.
The mass number is the sum of the protons and neutrons in the nucleus.

52. 4.3 Isotopes and Mass Number

53. 4.3 Mass of Atoms
One atomic mass unit (amu) is defined as 1/12th the mass of a carbon-12 atom.
One amu is nearly, but not exactly, equal to one proton and one neutron.

54. 4.3 Mass Number of Atoms
The atomic mass of an element is the weighted average mass of the isotopes of that element.

55. Mass Number
Mass number is the number of protons and neutrons in the nucleus of an isotope:
Mass # = p+ + n0
Nuclide p+ n0 e-
Mass #
Oxygen - 10 - 33 42
- 31 15 18 8 8 18
Arsenic 75 33 75
Phosphorus 16 15 31

56. Isotope Symbols
Contain the symbol of the element, the mass number and the atomic number.
Mass
number X
Superscript →
Atomic
number
Subscript →

57. Br Symbols 80 35 Find each of these: number of protons
number of neutrons
number of electrons
Atomic number
Mass Number 80 Br 35

58. Symbols
If an element has an atomic number of 34 and a mass number of 78, what is the:
number of protons
number of neutrons
number of electrons
complete symbol

59. If an element has 91 protons and 140 neutrons what is the
Symbols
If an element has 91 protons and 140 neutrons what is the
Atomic number
Mass number
number of electrons
Isotope symbol

60. Symbols If an element has 78 electrons and 117 neutrons what is the
Atomic number
Mass number
number of protons
complete symbol

61. We can also put the mass number after the name of the element:
Naming Isotopes
We can also put the mass number after the name of the element:
carbon-12
carbon-14
uranium-235

62. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.
Protons
Electrons
Neutrons
Nucleus
Hydrogen–1
(protium) 1
Hydrogen-2
(deuterium)
Hydrogen-3
(tritium) 2

63. Isotopes Elements occur in nature as mixtures of isotopes.
Isotopes are atoms of the same element that differ in the number of neutrons.

64. Atomic Mass How “heavy” (mass) is an atom of oxygen?
It depends, because there are different kinds of oxygen atoms.
We are more concerned with the average atomic mass.
This is based on the abundance (percentage) of each variety of that element in nature.
We don’t use grams for this mass because the numbers would be too small.

65. Measuring Atomic Mass
Instead of grams, the unit we use is the Atomic Mass Unit (amu)
It is defined as one-twelfth the mass of a carbon-12 atom.
Carbon-12 chosen because of its isotope purity.
Each isotope has its own atomic mass, thus we determine the average from percent abundance.

66. To calculate the average:
Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.
If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

67. Composition of the nucleus
Atomic Masses
Atomic mass is the average of all the naturally occurring isotopes of that element.
Isotope
Symbol
Composition of the nucleus
% in nature
Carbon-12
12C
6 protons
6 neutrons
98.89%
Carbon-13
13C
7 neutrons
1.11%
Carbon-14
14C
8 neutrons
<0.01%
Carbon =

68. Ex: Oxygen has three isotopes
Isotope Mass in amu Abundance
168O %
178O %
188O %
x = amu (for SF)
x = amu
x = amu
Atomic Mass O = amu (SF)

69. 4.3 Check
An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A. 38 B. 40 C. 19 D. unable to determine

70. 4.3 Check
Elements with the same number of protons and differing numbers of neutrons are known as what?
A. isotopes
B. radioactive
C. abundant
D. ions

71. 4.4
RAdioactivity

72. 4.4 Unstable Nuclei and Radioactive Decay
Review Vocabulary element: a pure substance that cannot be broken down into simpler substances by physical or chemical means

73. 4.4 Unstable Nuclei and Radioactive Decay
New Vocabulary
radioactivity
radiation
nuclear reaction
radioactive decay
alpha radiation
Main Idea
alpha particle
nuclear equation
beta radiation
beta particle
gamma rays
Unstable atoms emit radiation to gain stability.

74. 4.4 Radioactivity
Nuclear reactions can change one element into another element.
In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity.
The rays and particles emitted are called radiation.
A reaction that involves a change in an atom's nucleus is called a nuclear reaction.

75. 4.4 Radioactive Decay
Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay.
Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements.

76. 4.4 Radioactive Decay
Alpha radiation is made up of positively charged particles called alpha particles.
Each alpha particle contains two protons and two neutrons and has a 2+ charge.

77. The mass is conserved in nuclear equations.
4.4 Radioactive Decay
The figure shown below is a nuclear equation showing the radioactive decay of radium-226 to radon-222.
The mass is conserved in nuclear equations.

78. Each beta particle is an electron with a 1– charge.
4.4 Radioactive Decay
Beta radiation is radiation that has a negative charge and emits beta particles.
Each beta particle is an electron with a 1– charge.

79. 4.4 Radioactive Decay

80. Gamma rays are high-energy radiation with no mass and are neutral.
4.4 Radioactive Decay
Gamma rays are high-energy radiation with no mass and are neutral.
Gamma rays account for most of the energy lost during radioactive decay.

81. Few exist in nature—most have already decayed to stable forms.
4.4 Radioactive Decay
Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus.
Few exist in nature—most have already decayed to stable forms.

82. 4.4 Check
A reaction that changes one element into another is called what? A. chemical reaction B. beta radiation C. nuclear reaction D. physical reaction

83. Why are radioactive elements rare in nature?
4.4 Check
Why are radioactive elements rare in nature?
A. They do no occur on Earth.
B. Most have already decayed to a stable form.
C. They take a long time to form.
D. They are too hard to detect.