1. Atoms: The Building Blocks of Matter
Ch. 3

2. Dimensional Analysis
*A method of problem-solving using conversion factors Conversion Factor *Is essentially an equality ex/ 12 inches = 1 foot *Is written as a ratio to cancel units 12 inches OR 1 foot 1 foot 12 inches

3. Dimensional Analysis Problems
1. Convert 15 feet to inches. 2. Convert 176 feet to yards.

4. 1. Convert 2,500 inches to yards. 2. Convert 0.0034 miles to inches.

5. 25 days to seconds
1,000,000 minutes to years

6. Early atomic theory Democritus (400 B.C.) Aristotle
Atoms are nature’s basic particles
“atom”  Greek word meaning “indivisible”
Aristotle
Disagreed, thought matter was continuous
Aristotle's theory prevailed for next 2000 yrs.

7. 1700s
1st experimentation
Definition of element (pure sub. made of 1 kind of atom)
Elements combine  compounds

8. Late 1700s Quantitative studies of reactions
law of conservation of mass

9. Dalton’s Atomic Theory
All matter composed of atoms
Atoms…
of same element are identical; atoms of diff. elements are diff.
cannot be divided, created, destroyed
combine in simple whole # ratios to form compounds (Law of Definite Proportions)
are combined, separated or rearranged in chem. rxns.

10. Modern Atomic Theory Not all of Dalton’s ideas were correct
Atoms can be divisible
Atoms of same element can have diff. masses
Most still holds true

11. Sec. 2 - Structure of the Atom
nucleus – protons & neutrons
electron cloud

12. Discovery of the e- (1897)
Cathode ray tube – electric current passed through gases, found neg. charged particles
JJ Thomson
Did more expts. and found particles identical (no matter which gas used)
Named them electrons

13. Choc. chip cookie model Millikan Oil drop exp.
Mass of e- extremely small, neg. charged
Atom is neutral, therefore must contain + charge also
Choc. chip cookie model +

14. Discovery of Nucleus Rutherford Chadwick discovered
1900
Gold foil exp.
Confirmed dense
nucleus with + charge
Chadwick discovered
neutrons ~30 yrs. Later

15. Modern atomic model nucleus: p+ and n0 e- cloud
All the mass, very little space
e- cloud
No mass, lots of space

16. Nuclear forces Like forces repel, normally
BUT when protons are really close there is a strong attractive force
Same with neutrons
Called nuclear forces (energy, bombs)

17. Size of atom Tiny Radius  from center of nucleus to edge of e- cloud
Measured in pm (10-12)
Atomic radii range from pm

18. Sec. 3 - Counting Atoms Atomic # Ex: oxygen is 8  8 p+ and 8 e-
# of protons in nucleus
Determines what element
Ex: oxygen is 8  8 p+ and 8 e-

19. Mass #
Total # of p+ and n0 in an isotope
Calculate # of neutrons:
Mass # - atomic #
(p + n) – (p) = n

20. Isotopes Atoms of same element with diff. # neutrons Diff. masses
Ex: hydrogen
H protium %
H deuterium %
H tritium trace, synthetic
*Don’t differ much in chem. props. 1 1 2 1 3 1

21. Isotope symbols
Hyphen uranium-235
Nuclear symbol U
235 92

22. Charges Br Ca+2 Atomic # Mass # Protons Neutrons electrons 35 80 4536
Ca+2 20 40 18 80 35 80 35 40 20

23. masses so small, came up with scale that is relative
amu’s
atomic mass units
masses so small, came up with scale that is relative
amu = mass of 1/12 mass of carbon-12 atom
Average atomic masses
# on periodic table
Decimals  averages

24. Copper – 63 53%
Copper – 64 47%
Arsenic – 74 13%
Arsenic – 75 80%
Arsenic – 76 7%

25. Relating Mass to Numbers of Atoms
The mole is the SI unit for amount of substance
A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.

26. Avogadro’s Number Avogadro’s number 6.022 1415  1023
is the number of particles in exactly one mole of a pure substance.
Can find:
Atoms  moles
Moles  atoms

27. Molar Mass Molar mass - The mass of one mole of a pure substance
usually written in units of g/mol
numerically equal to the atomic mass of the element in amu’s.

29. Examples
What is the mass in grams of 3.50 mol of the element copper, Cu?
A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced?

30. How many moles of silver, Ag, are in 3.01  1023 atoms of silver?
What is the mass in grams of 1.20  108 atoms of copper, Cu?

31. Chapter Review
Pg. 89
# 1-3, 5-7, 11, 14-21, 27