1. Chapter 11 Introduction to Atoms

2. An atom is the smallest particle into which an element can be divided and still be the same substance.
See timeline handout for the development of the model of the atom.
Identify atom models of Dalton, Thomson, Rutherford, Bohr, and the Modern Model.

3. Structure of the atom
nucleus
energy
level

4. What do I need to know? Know the scientist
their contribution to the developing model of an atom (their experiment)
their atom model!

5. Dalton’s Atomic Theory
Today, we are going to look at the development of the atomic theory. We are going to define Dalton’s atomic model.

6. Which is not part of Daltons Theory?
Atoms cannot be divided, created, or destroyed.
All atoms of an element are identical.
Chemical Reactions destroy matter.
Atoms combine in specific ratios.

7. Which is not part of Daltons Theory?
Atoms cannot be divided, created, or destroyed.
All atoms of an element are identical.
Chemical Reactions destroy matter.
Atoms combine in specific ratios.
Chemical Reaction Rearrange atoms.

8. Thomson’s Atomic Model
Then we are are going to look at Thomson’s modifications, or Thomson’s atomic model.

9. Thomson’s Atomic Model: A sphere with an evenly distributed positive charge with negative electrons mixed in - - - - -
Thomson’s Atomic Model said that an atom is a sphere with an evenly distributed positive charge with negative electrons mixed in - -

10. Cathode Ray Tube
Thomson began experimenting on a cathode ray tube to see if rays had charges.

11. Cathode Ray Tube
In his experiment, Thomson shot cathode rays through a tube and saw the wire bend towards the positive plate.

12. Why did Thomson’s experiment lead him to believe cathodes were
negatively charged?
The wire bent towards the positive

13. Thomson’s Atomic Model: A sphere with an evenly distributed positive charge with negative electrons mixed in - - - - - -
As a reminder, Thomson’s Atomic Model said that an atom is a sphere with an evenly distributed positive charge with negative electrons mixed in. Just like a plum pudding. -

14. What charge does the red section have?
Positive.

15. Why are there both positive
and negative charges?
The overall net charge is neutral.

16. Rutherford Atomic Model
Then we will define Rutherford’s Atomic Model.

17. Rutherford’s Atomic Model: atoms consist of a positive center surrounded by electrons in negative space
Positive Center
Atoms have a positive center surrounded by electrons in negative space

18. Gold Foil Experiment
Here Rutherford shown alpha particles at a piece of gold foil and expected the particles to travel straight through

19. Reflection
Instead the light was sometimes reflected.

20. Dense Space= Reflected by Foil
This meant the alpha particle was hitting a dense space when it was reflected.

21. Empty Space= Through Foil
This meant the alpha particle was hitting empty space, when it traveled through.

22. Positive central nucleus
Rutherford concluded there was a positive central core, or the nucleus

23. Electrons in empty space
And also that that electrons are in the negative space.

24. Rutherford’s Atomic Model: atoms consist of a positive center surrounded by electrons in negative space
Positive Center
So, he knew that atoms have a positive center surrounded by electrons in negative space

25. Where is the positive charge located?
The nucleus

26. What experiment did Rutherford use?
The Gold Foil Experiment.

27. Why is the atom mostly empty space?
Most of the particles went through the foil.

28. Bohr’s Atomic Model
Bohr’s Atomic Model will also be discussed.

29. Bohr’s Atomic Model: electrons move in orbitals and, when they change orbitals, they gain energy

30. What did he observe to discover this model?

31. Modern Atomic Model
And finally we will address the modern atomic model.

32. Modern Atomic Model

33. Modern Atomic Model: orbitals are clouds and shows where electrons are most likely to be
The modern model is similar to Bohrs model except it looks at orbitals as clouds. Instead it shows the area where the electron is most likely to be.

35. Which model defines the characteristics
of an atom?
Dalton

36. Which model has a positive sphere with negative charges embedded?
Plum Pudding

37. Which scientist introduced orbitals?
Rutherford

38. How is Bohr’s Model different
from Rutherford’s?
Bohr included oribtals.

39. What is the key characteristic of modern
atomic theory?
Electron cloud

40. Structure of the atom
The atom contains a nucleus surrounded by one or more electrons
The nucleus contains protons and neutrons.
Draw an atom here
(Page 320)

41. Structure of the atom
nucleus
energy
level

42. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral
Electron
Negative
(-)
Outside nucleus
1/2000
amu

43. Particle
Charge
Location
Mass
Proton

44. Particle
Charge
Location
Mass
Proton
Positive
(+)

45. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus

46. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu

47. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron

48. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral

49. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral

50. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral

51. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral
Electron

52. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral
Electron
Negative
(-)

53. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral
Electron
Negative
(-)
Outside nucleus

54. Particle
Charge
Location
Mass
Proton
Positive
(+)
Inside nucleus
1 amu
Neutron
Neutral
Electron
Negative
(-)
Outside nucleus
1/2000
amu

55. Terms to copy in notes:
atomic number – the number of protons in the nucleus of an atom.
(*The number of protons identifies an element!)
atomic mass – the average mass of one atom of an element.
atomic mass unit (amu) – a measurement of the mass of one proton or one neutron.

56. Know the Following Elements!
The first 20 elements and symbols, plus 7 others, must be properly identified together.
iron copper
silver gold
mercury tin lead
The symbols must be written in correct form.
Spelling counts!

57. Chemical Symbols Hydrogen symbol is H Cobalt symbol is Co
A chemical symbol is one or two letter(s) representing an element.
If the symbol is one letter, it is a printed capital.
Hydrogen symbol is H
If two letters, the first is a printed capital and second is lower case.
Cobalt symbol is Co

58. Electrons
Electrons are located in an electron cloud around the nucleus.
There are different energy levels (“orbits” in the Bohr model) that electrons fill.
1st energy level can hold 2 electrons
2nd can hold 8 electrons
3rd can hold 18 electrons
4th can hold 32 electrons

59. Energy Levels of carbon atom

60. Fe Today’s periodic table is based on atomic number.
Each element’s square contains:
atomic number (protons)
chemical symbol
element name
atomic mass (protons &
neutrons)
This is an average 26 Fe
Iron
55.847

61. How to find the number of neutrons in an atom
Round the atomic mass to the nearest whole number.
Subtract the number of protons (atomic number).
The difference is the number of neutrons.
boron atomic mass (protons + neutrons)
rounded
atomic number (protons)
6 neutrons

62. Aluminum
atomic mass
rounded
- atomic number
neutrons

63. Gaining or losing a neutron makes an atom an isotope.
Isotopes are still the same element, just more or less neutrons.
carbon 12
has 6 neutrons (always 6 protons)
carbon 14
has 8 neutrons (always 6 protons)
The 12 refers to
the mass number
(protons + neutrons)

64. Practice calculating the number of neutrons in an atom
Number a blank sheet of paper 1 to 10.
Write the name for each element from the periodic table for elements 1-10.
Use the right side of your paper to calculate the number of neutrons for elements 1-10.
Write your answer next to the elements name.

65. Valence electrons are electrons farthest away
Valence electrons are electrons farthest away from the nucleus (outer energy level).
- involved with chemical reactions.
- gives an atom its chemical characteristics.
- can be shared, or transferred.
- Atoms with a full valence energy level are most stable (less reactive).

66. hydrogen oxygen carbon neon
electron dot diagram – represents the valence electrons of an element.
- uses an element symbol surrounded by dots representing valence electrons.
H O C Ne
hydrogen oxygen carbon neon

67. The Periodic Table of Elements
Chapter 12 Notes
The Periodic Table of Elements
In 1869 a Russian scientist Dmitri Mendeleev arranged elements in order of increasing atomic mass, and chemical properties.
He used his table to predict properties of elements not yet discovered!

68. Fe Today’s periodic table is based on atomic number!
Each element’s square contains:
atomic number (protons)
chemical symbol
element name
atomic mass (protons &
neutrons)
This is an average 26 Fe
Iron
55.847

69. An element’s properties can be predicted by its location on the periodic table.
Groups or families:
vertical columns numbered 1-18.
elements have similar properties
Periods:
across rows numbered 1-7
elements have predictably different patterns.

70. Metals Metals are found to the left of the stair step.
Physical properties:
Hardness
Shininess (luster)
Malleability (pound into shapes)
Ductility (drawn out into a wire)
Good conductors
Magnetic (Co, Ni, Fe)
Mostly solids at room temp.

71. Metals Chemical properties: wide range
Some violently react with water (Na, K)
Some unreactive (Au, Cr)
Some corrode (react slowly with O2 and flake off)
Alloys (mixture of metals)
bronze (Cu + Sn)
stainless steel

72. Metals
Elements are increasingly nonmetallic reading left to right.
Tend to lose electrons forming
positive ions (1+, 2+)
Alkali Metals
Group 1 (1 valence electron)
Most reactive metals!
Very soft & shiny

73. Metals Alkaline Earth Metals Group 2 (2 valence electrons)
Not as reactive as Group 1 but more reactive than most metals.
Fairly hard, grey-white color
Good conductors of electricity

74. Metals Transition Metals Groups 3-12
Fairly stable, react slowly with H2O
Similar reactivity between columns
Hard and shiny
Good conductors of electricity

75. Metals Lanthanides and Actinides Called rare earth metals
Fit in Periods 6 and 7 between alkaline earth metals and the transition metals.
Placed below periodic table for convenience.
Soft, malleable, shiny, very conductive

76. Nonmetals Located right of the stair step Physical properties:
Most are gases at room temp. (low boiling point).
dull
brittle
lower densities
poor conductors of heat & electricity

77. Nonmetals Halogen Family Chemical properties:
Most readily form compounds
Will take electrons from metals forming
negative ions (1-, 2-)
Will also share electrons
Many form diatomic molecules (O2, N2, H2)
Halogen Family
Group 17 (7 valence electrons)
Very reactive!
Dangerous to humans

78. Nonmetals Noble Gases Hydrogen Group 18 Chemically stable (unreactive)
Do not gain, lose, or share valence electrons
Hydrogen
Alone in upper left corner
Simplest element
Not grouped in a family

79. Metalloids Along the stair step (7 elements)
Have some properties of metals & nonmetals
Used to make semiconductors