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CHEMISTRY of the Atom
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CHEMISTRY of the Atom
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PARTICLES:
Mass
Charge
Symbol
Nucleus:
 PROTON
1 amu
+1
H+, H, p
 NEUTRON
1 amu
0
n
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 ELECTRON very small -1
eThe particle is said to “hold” atoms together in molecules.
© Copyright 1998-2000 R.J. Rusay
Periodic Table
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• Mendeleev’s Table 1868-1871
Mural at St.Petersburg University, Russia
© Copyright 1998-2000 R.J. Rusay
Periodic Table
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Elements are classified by:
properties & atomic number
metals, non-metals, metalloids
Groups or Families (vertical)
1A = alkali metals
2A = alkaline earth metals
7A = halogens
8A = noble gases
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Periods (horizontal)
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Group 1 and Group 2 Metals
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Modern Periodic Table
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From Los Alamos National laboratory:
© Copyright 1998 R.J. Rusay
Using the Periodic Table
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Atoms, Molecules & Ions
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Atoms:
• # Protons = Atomic Number
• Atomic Mass = # Protons + # of
Neutrons
• Isotope: same atomic number but
different atomic mass
• Periodic Table atomic mass is a
weighted average of isotopic masses
© Copyright 1998-2000 R.J. Rusay
Atoms, Molecules & Ions
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Atomic Mass of Carbon:
Exact Mass
12.00000
98.98
13.00335
1.110
14.00
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% Occurence
negligible
What is the “weighted” atomic mass?
© Copyright 1998-2000 R.J. Rusay
Atoms, Molecules and Ions
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Atomic Number = 6 (atom’s identity)
Carbon
Atomic Mass = 13 (isotope 13)
6 protons; # neutrons = 13 - 6
neutral atom has 6 electrons
© Copyright 1998-2000 R.J. Rusay
Atomic Symbols
Mass number 
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K
19
 Element Symbol
Atomic number 
Atoms, Molecules and Ions
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Atomic Number = 12 (atom’s identity)
Atomic Mass = 24
12 protons; # neutrons = 24 - 12
neutral atom has 12 electrons
Ion contains 10 electrons: symbol?
24
12
+2
Mg
• 12 p+ + 10e- = +2
© Copyright 1998-2000 R.J. Rusay
Atoms, Molecules and Ions
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Atomic Number = 17 (atom’s identity)
Atomic Mass = ?
# protons = ? ; # neutrons = ?
neutral atom has ? electrons
Ion contains 18 electrons: symbol?
35
17
-1
Cl
• 17 p+ + 18e- = -1
© Copyright 1998-2000 R.J. Rusay
Ions
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Cation: A positive ion
 Mg2+, NH4+
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Anion: A negative ion
 Cl, SO42
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Ionic Bonding: Force of attraction
between oppositely charged ions.
Molecules
Neutrally Charged
 Eg. Salt: NaCl -> 1 Na+ and 1 Cl  What is the proportion of ions for a
compound formed from Mg ion and
chlorine?
 Mg2+ and Cl
 1 Mg2+ combines with 2 Cl
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Chemical Formulas
Molecular Formula:
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Elements’ Symbols = atoms
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Subscripts = relative numbers of
atoms
 How many atoms of each element are in
the following componds?
 MgCl2
CCl4
NaOH
(NH4) 2CO3
 C20H26N2O (Ibogaine, not ionic)
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