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ATOMS AND Isotopes
Fundamental Chemical Laws
1
2
• Lavosier = Law of Conservation of Mass
– During a chemical change the mass of the reactants
must equal the mass of the products.
– The number and kinds of atoms are the same on each
side of a chemical equation
• Proust = The Law of Definite Proportions
– A given
i
compound
d always
l
contains
t i the
th same
proportions of elements by mass
• Dalton = 4 postulates (proved the law above)
– When 2 elements form a series of compounds, the
ratios of the masses of the second element that
combine with 1 gram of the first element can be
reduced to small whole number ratios
– READ TEXT
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ATOMIC COMPOSITION
J.J. Thomson did experiments with a
cathode ray tube and discovered that the
atom contained a negative charge
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• Protons
– + electrical charge
– mass = 1.672623 x 10-24 g
– relative mass = 1.007 atomic
mass units (amu)
The modern view of the
atom was developed by
Ernest
Rutherford
R th f d
• Electrons
– negative electrical charge
– relative mass = 0.0005 amu
of New Zealand
(1871--1937).
(1871
• Neutrons
–
–
no electrical charge
relative mass = 1.009 amu
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AN ATOMS COMPOSITION
Atomic Number, Z
The atom is mostly empty space
All atoms of the same element
have the same number of
protons in the nucleus, Z
•protons and neutrons in the nucleus.
•the number of electrons is equal to the
number
b off protons
t
in
i neutral
t l atom
t
•electrons in space around the nucleus.
13
Al
•extremely small. One teaspoon of water has
3 times as many atoms as the Atlantic Ocean
has teaspoons of water.
26.981
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Atomic number
Atom symbol
Atomic weight
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Mass Number, A
Mass Number
• C atom with 6 protons and 6 neutrons
is the mass standard
• = 12 atomic mass units
• There exist varieties of an element
called isotopes.
• They have the same number of protons,
but various numbers of neutrons,
th f
therefore
having
h i
various
i
mass numbers
b
+
• Mass Number = the total # p (1 a.m.u.)
and the number of n0 (1 a.m.u.)
• For every element there are at least 2
isotopes (sometimes more)
• Mass Number (A)
= # protons
t
+ # neutrons
t
• A boron atom can have
A = 5 p + 5 n = 10 amu
A
10
Z
5
B
9
Isotopes
10
Complete the isotope chart
Name of
Isotope
• Atoms of the same element (same Z)
but different mass number (A).
• Boron
Boron--10 has 5 p and 5 n: 105B
• Boron
B
Boron-11 h
has 5 p and
d 6 n: 115B
Isotope
Symbol
#p+
#n0
#e-
16
18
16
Carbon -14
23 Mg
12
11B
10B
Isotopes &
Their Uses
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Complete the isotope chart
Name of
Isotope
Isotope
Symbol
#p+
#n0
#e-
Carbon -14
14 C
6
6
8
6
Bone scans with
radioactive
technetium--99.
technetium
99
Magnesium23
23 Mg
12
12
11
12
99
Sulfur -34
34 S
16
16
18
16
12
43Tc
Emits gamma rays
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