This document provides an overview of key concepts in general chemistry including: 1. The physical and chemical properties of matter, the different physical states of substances, and examples of physical and chemical changes. 2. The structure of atoms including protons, neutrons, electrons, and isotopes. Key atomic structure concepts like atomic number and mass number are introduced. 3. Energy levels of electrons in atoms, specifically the Bohr model of the hydrogen atom. Light is emitted when electrons change energy levels. 4. The quantum mechanical model which describes electrons existing as waves around the nucleus at different energy levels rather than classical orbits.

1. Matter
and
Change P Squires
General Chemistry
2005-2006

2. Observing Chemical
Change
• Open book to page 55 and
conduct Discovery Lab
• (50 pts)

3. Properties of Matter
•What is a substance?
• Physical Properties
• Chemical Properties

4. Physical States
Solid What are some
Liquid characteristics
of each?
Gas
Plasma

5. Give the physical state of each of
these:
1. Silver Solid
2. Gasoline Liquid
3. Helium Gas
4. Rubbing alcohol Liquid
5. Air Gas
6. Glass Solid or liquid
7. Lightning Plasma

6. Plas
ma

7. Physical Changes
• Physical changes only
involve changes in state or
appearance.
• What are some examples of
physical change?

8. Catch words for Physical
Change
• Boil •Split
• Freeze •Grind
• Melt •Cut
• Condense
•Crush
• Break
•Bend

9. Chemical Changes
• Chemical changes and
chemical properties always
produce new substances.

10. Chemical or physical change ???
• Food spoiling Chemical
• Nail rusting Chemical
• Oil burning Chemical
• Sugar dissolving Physical
• Water boiling Physical
• Firefly flashing Chemical
• Egg cooking Chemical
• Snowflake melting Physical

11. Percent mass
Percent mass (%) = mass of element_ x 100
mass of compound

12. Calculations
1. A 78.0 g sample of an unknown
compound contains 12.4 g of
hydrogen. What is the percent by mass
of hydrogen in the compound?
2. If 1.0 g of hydrogen reacts completely
with 19.0 g of fluorine, what is the
percent by mass of hydrogen in the
compound that is formed?

13. Pure Substances
• Elements are the building blocks of
matter.
• Atoms are the smallest part of an
element.

14. Mixtures
… do not have a definite
composition
… are either heterogeneous,
with clearly visible components
… or homogeneous,
which are uniform in
appearance

15. Solutions
• Solutions are homogeneous
mixtures containing a solute
which is dissolved in a solvent.

16. Classify as heterogeneous,
or homogeneous (solution)
• Blood Homogeneous
• Choc. chip ice cream Heterogeneous
• Brass (Cu-Zn alloy) Homogeneous
• Homogenized milk Homogeneous
• Hummingbird food Homogeneous
(solution)

17. We separate mixtures …
… based on differences in the
chemical and physical
properties of the components in
the mixture.

18. Separating Mixtures
• Quick Lab Handout
• (50 points)

19. How would you separate the
following?
Aluminum filings and iron filings?
Saw dust and sand?
Salt and powdered charcoal?
Water and alcohol?

20. Elements
• A pure substance that can not be
separated into simpler substance by
physical or chemical means.

21. Compounds
• A combination of two or more different
elements that are combined
chemically.
• What are some examples
of compounds?

22. The Law of Conservation of
Mass
Matter can neither be
created or destroyed
during a chemical
reaction.

23. Law of Definite Proportions
Elements comprise
compounds in definite
proportions by mass.

24. Law of Multiple Proportions
When different compounds are
formed, they combine in
whole number ratios.
H2O H2O2

25. ChemLab
• Read and complete ChemLab
page 78. (100 points)
• Answer Questions at end:
Analyze and Conclude.

26. Structure of the
Atom

27. Part of the Atom
• Electron
• Proton
What charge does each have?
• Neutron
Where are they found?
Which ones make up the mass of the
atom?
Which ones make up the size of the
atom?

28. How Do Atoms Differ?
•Atomic Number
•Atomic Mass

29. Element Atomic Protons Electrons Atomic
Number Mass
He 2
Pb 82
8
30

30. Mass Number
Number of neutrons =
mass number – atomic number

31. Isotopes …
…of the same element have the
same number of protons and
electrons but different numbers of
neutrons.
Therefore, isotopes of the same
element have different masses.

32. Symbols for Isotopes
Mass number
A is the
A Symbol
E
symbol
for mass Z of
Element
number
Z is the symbol for
Atomic
number
atomic number

33. MiniLab
• Do modeling isotope lab on
page 102.

34. Energy
and
Electrons

35. Light and Energy
• Frequency = f or f with units of
Hertz (Hz)
• Wavelength = λ with units of
meters (m)

36. What is the relationship
between frequency and
wavelength?

39. For electromagnetic
energy, the equation is:
c = fλ
c is the speed of light
c = 3.00 x 10 m/sec
8

40. Electromagnetic
Spectrum
• Electromagnetic waves
carry energy.
• Light is part of the
electromagnetic spectrum

41. The Electromagnetic Spectrum
gamma rays
microwaves
visible light
ultraviolet
infrared
X-rays
radar
radio
TV
Shorter wavelength Longer wavelength
Higher frequency Lower frequency
Higher energy Lower energy

42. gamma rays
X-rays
400 nm
ultraviolet
visible light
infrared
microwaves
Increasing energy
radar
TV
700 nm
radio
The Electromagnetic Spectrum

43. The visible spectrum was
discovered by …
Dr. Roy G. Biv
Red Orange Yellow Green Blue Indigo Violet
700 nm 400 nm
Lower energy Higher energy

44. Niels Bohr
Bohr said that electrons could exist only
in certain discrete energy levels …
… and that electrons can only change
energy levels when they absorb or give
off a certain amount of energy. (1913)

45. Hydrogen
atom
Discrete energy levels for electrons
electron nucleus

46. Hydrogen
atom
Electrons can exist in this orbit,

47. Hydrogen
atom
…or in this orbit,

48. Hydrogen
atom
…or in
this orbit,

49. Hydrogen
atom
…but not in between the orbits.

50. Hydrogen
atom
Unless the electron is
absorbing energy, or …
Giving off energy

51. When high voltage is connected to
the hydrogen discharge tube, a
bluish light is given off.
When observed through a
diffraction grating, specific lines
of color are observed.

52. The electron in a hydrogen
atom gains energy from the
electricity passing thru the
tube and …
… the electron moves up to a
higher energy level.

53. The electron in the excited
state is “unstable”.
The electron drops to a lower
energy level, and …
… gives off light of a certain
energy and wavelength.

54. Hydrogen
atom

55. Hydrogen
The electron
absorbs atom
energy and …
ener
g y

56. Hydrogen
atom
…the
electron is
elevated
to the next
energy level

57. Hydrogen
atom
The electron is
unstable and
“wants” to
return to a lower
energy level

58. Hydrogen
atom
Light of a
particular
wavelength
is given off

59. Helium

60. Neon

61. Hydrogen

62. “Regardless of it’s
shortcomings and the
modifications that were later
applied, Bohr’s model of the
atom was the first
successful attempt to make
the internal structure of the
atom agree with
spectroscopic data.”
Asimov, 1964

63. Quantum
Mechanical Model of
the Atom
1. A small, dense positively
charged nucleus which
contains protons and neutrons.
2. Electrons which exist outside of
the nucleus at …
– various distances from the nucleus,
and at …
– various energy levels.

64. The Electrons
3. The electrons can have both a mass,
as does matter, and a wavelength,
as does light energy.
4. The electrons themselves are not
little solid spheres in orbit around the
nucleus, but exist as a “fog” of half-
energy, half-matter. The electrons
can behave as either matter or
energy, depending on the
experiment.

65. Energy Levels
5. Based on the ideas of Bohr, the
electrons are located …
– … in major energy levels,
– … in energy sublevels within major
energy levels,
– … in orbitals within each sublevel.

66. Next up….
The Periodic Table