Download Ch. 5 Atomic Structure

Chapter 5
Atomic Structure and the
Periodic Table
Just How Small is an Atom?
You don’t need to write.
A penny contains about 2.4 × 1022 atoms.
 A speck 0.1 mm in diameter (about half the size
of a period at the end of the sentence) requires
one million atoms.
 It would require a million atoms, edge to edge,
to match the thickness of a page of paper.

History of the Development of Atomic Models
A.
Democritus (400 B.C.)
 1st suggested matter is made of atoms
 atom- means “indivisible”
John Dalton
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John Dalton (1766-1844),
was an English schoolteacher.
 Performed experiments to
test his atomic theory.

Formulated hypothesis and theories to
explain his observations.

History of the Development of Atomic Models
B. Dalton (1766-1844)
 Dalton’s
1.
Atomic Theory
All elements are composed of tiny
indivisible particles called atoms
Is this still true?
YES
Dalton’s Atomic Theory
2. Atoms of same element are identical.
The atoms of any one element are
different from those of any other
element.
Is this still true?
 atoms
of the same element can have
different masses (isotopes)
Dalton’s Atomic Theory
3. Atoms form compounds by
combining in whole number ratios
Is this still true?
 YES: Law of Definite Proportions
Dalton’s Atomic Theory
4. Chemical reactions occur when atoms
are separated, joined or rearranged.
Atoms of one element can never change
into another element.
Is this still true?
No, These changes CAN occur in nuclear
reactions!
Structure of the Atom

Nucleus:
 Electron Cloud:
– contains protons and neutrons -contains electrons
-takes up most of space
– takes up very little space
Discovery of Nucleus
C. Rutherford (1871-1937) discovered the nucleus by
shooting alpha particles (have positive charge) at a
very thin piece of gold foil
– he predicted that the particles would go right through the
foil at some small angle
Discovery of Nucleus
Discovery of Nucleus
some particles (1/8000) bounced back
from the foil
 this meant there must be a “powerful
force” in the foil to hit particle back

Predicted Results
Actual Results
Subatomic Particles
D. J.J. Thomson (1856-1904) – discovered
electrons in atoms; his model was of a
positive sphere with e- embedded in it.
E. Milliken (1868-1953) found the mass of the
electron
F. Goldstein found protons in 1886
G. Chadwick (1891-1974) found the neutron
Discovery of Electron
You don’t need to write.
resulted from scientists passing electric current
through gases to test conductivity
 used cathode-ray tubes
 noticed that when current was passed through a
glow (or “ray”) was produced

Discovery of Electron
This led scientists to believe there were negatively charged
particles inside the cathode ray
Properties of Subatomic Particles
Relative
Particle
Symbol
electrical
charge
Relative
Actual mass
mass
(g)
Electron
e-
1-
1/1840
9.11 × 10-28
Proton
p+
1+
1
1.67 × 10-24
Neutron
n0
0
1
1.67 × 10-24
How to find:
A.
B.
C.
# of protons = atomic number
# of neutrons = rounded mass #
– atomic #
# of electrons = # of protons
1.
Chemical Symbols
a) Printed: 1st letter capital, 2nd letter lower
case
b) Represents one atom of an element
Fe Cl B
2. Important principles about the atom
a)
b)
c)
d)
All atoms are electrically neutral (p+ = e-)
Nearly all mass is in the nucleus
Lots of space between nucleus and eEvery atom of the same element has the
same # of p+
3. Atomic Number is the # of p+
Element
Atomic #
# of Protons
Carbon
6
6
Phosphorus
15
15
Gold
79
79
4. Mass Number is the # of p+ + n0
Mass Number
Atomic Number
12
6
C
Element Symbol
5.
Isotope of an element- same # p+,
different # of n0
(Same atomic #, different mass #)
6. Atomic mass unit (amu)- defined
as 1/12 of the mass of a Carbon-12
atom
7. Atomic Mass- mass averaged of all the
isotopes of an element.
Mass Number
8. Isotopic Name:
Carbon-12 or Carbon-14
a.
21
10
Ne
p+
10
e-
10
n0
11
p+ 1
b. Hydrogen-3
e- 1
n0 2
c. Magnesium-27
27
12
Mg
Isotope Lab
Avg. mass = Mass (of that type of veggie)
# of pieces of that type of veggie
% abundance =
# of pieces of that veggie × 100
Total # of pieces of all veggies
Bell Work 9/21
The nucleus consist of ______ and _______. The ______
number of an atom gives the number of protons. The
_____ number gives you how many protons and neutrons
are in the nucleus.
_________
_________
23
_________
11
Na
Copper-63
Atoms that have the same _______ ________ but
different numbers of neutrons are ________ of the same
element. Since isotopes have different numbers of
neutrons, they have a different _______ ______.
C. Nuclear Symbols
 Chlorine-37
–atomic #:
17
–mass #:
37
–# of protons:
17
–# of electrons:
17
–# of neutrons:
20
37
17
Cl
Nuclear Symbol Examples
35
17
Cl
Atomic Number
Mass Number
17
35
Mg
Number of
Protons
Number of
Electrons
Number of
Neutrons
17
17
18
27
12
Atomic Number
12
Mass Number
27
Number of
Protons
Number of
Electrons
Number of
Neutrons
12
12
15
Average Atomic Mass
 weighted
average of all naturally
occuring isotopes
 on the Periodic Table
 round to 2 decimal places
Avg.
Atomic
Mass
(mass)(% )  (mass )(% )

100
Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if
its abundance in nature is 99.76% 16O, 0.04%
17O, and 0.20% 18O.
Avg.
(16)(99.76 )  (17)(0.04)  (18)(0.20)
Atomic 
 16.00
100
amu
Mass
Average Atomic Mass

EX: Calculate the avg. atomic mass of oxygen if
its abundance in nature is 99.76% 16O, 0.04%
17O, and 0.20% 18O.
Avg.
(16)(99.76 )  (17)(0.04)  (18)(0.20)
Atomic 
 16.00
100
amu
Mass
E. Average Atomic Mass

EX: Find chlorine’s average atomic mass if
approximately 8 of every 10 atoms are
chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
(35)(8)  (37)(2)

 35.40 amu
10
Example:
A sample of cesium is 75% 133Cs, 20%
and 5% 134Cs. What is the average atomic
mass?
132Cs
Answer:
.75 x 133 = 99.75
.20 x 132 = 26.4
.05 x 134 = 6.7
132.85 = average atomic mass