Chemical Ideas 2'1'

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Chemical Ideas 2.1.

• A simple model of the atom.

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Whats inside?
In the nucleus?
Protons
And around the nucleus?
Neutrons
Electrons
3
How are they different?
Location
Mass
Charge
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Nuclear symbols
p n
Mass number ?
Na
23
11
p ( e-)

• 11
• 11
• 12

Atomic number ?
p?
e-?
n?
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What are isotopes?
17
17
p?
p?
Cl
Cl
17
17
35
37
e-?
e-?
17
17
18
20
n?
n?

• Atoms of the same element with
• The same atomic number but different mass numbers
• Same number of protons but different numbers of
  neutrons

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Why is 35Cl O.K.?
Chlorine always has an atomic number of 17!
Relative isotopic mass
Cl
Cl
37
35
17
17
Cl-37
Cl-35
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So what is relative atomic mass?
Cl-35
75
25
Cl-37
9
Relative atomic mass is the average of the
relative isotopic masses
Cl-35
75
Cl-37
25
How do we get a relative atomic mass of 35.5?
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What 2 things did we need to know?
Relative isotopic masses.
The relative abundances.
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How do we find them out?
Use a mass spectrometer
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Mass spectrometry
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Mg
Mg
e-
e-
15
Cl-35
Cl-37
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A mass spectrum
100
80
60

40
20
mass
35
37
36
17
A mass spectrum
Try W and Y!
100
80
60

40
20
mass
24
26
25