Download CHEMISTRY of the Atom

Atoms-Molecules-Ions
Dr. Ron Rusay
Fall 2001
© Copyright 2001 R.J. Rusay
National Prayer & Remembrance
Noon, September 14, 2001
Let us join these 6th graders
in Nablus Palestine in a
moment of silence to
remember & pray for the
fallen.
Modern History of the Atom
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1
1909: Millikan determines charge and mass of e
1913-19: Rutherford & Bohr’s atom;
The proton.
http://www.yrbe.edu.on.ca/~mdhs/science/chemistry/ch2_2.htm

1927: Waves & Particles, Quantum Mechanics
http://www.nmsi.ac.uk/on-line/electron/section3/1927.html

1932: James Chadwick “discovers” the neutron
http://www.nmsi.ac.uk/on-line/electron/section3/1932a.html
© Copyright 1998, 1999, 2000, 2001 R.J. Rusay
CHEMISTRY of the Atom
Ernest Rutherford (1871-1937)
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Modern History of the Atom
1

1897: J.J. Thomson “discovers” the electron:
http://www.nmsi.ac.uk/on-line/electron/section2/
Photo © The Nobel Foundation
http://pl.nobel.se/laureates/physics-1906-1-bio.html
© Copyright 1998,1999, 2000, 2001 R.J. Rusay
Milliken Oil Drop Experiment
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View of the Atom
CHEMISTRY of the Atom
1
PARTICLES:
Mass
Charge
Symbol
Nucleus:
 PROTON
1 amu
+1
H+, H, p
 NEUTRON
1 amu
0
n
_________________________________________
 ELECTRON very small -1
eThe particle is said to “hold” atoms together in molecules.
© Copyright 1998-2001 R.J. Rusay
Atoms, Molecules & Ions

1
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
1

Atomic Mass of Carbon:
Exact Mass
12.00000
98.98
13.00335
1.110
14.00

% Occurence
negligible
What is the “weighted” atomic mass?
© Copyright 1998-2000 R.J. Rusay
Atoms, Molecules and Ions
1
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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 1998-2001 R.J. Rusay
Atomic Symbols
Mass number 
39
K
19
 Element Symbol
Atomic number 
The Sodium Atom
The Fluorine Atom
An Unknown Atom
Name the atom.
Atoms, Molecules and Ions
1
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Atomic Number = 12 (atom’s identity)
Atomic Mass = 24
12 protons; # neutrons = 24 - 12
neutral atom has 12 electrons
With ten electrons an ion is formed:
24
12
© Copyright 1998-2001 R.J. Rusay
+2
Mg
Atoms, Molecules and Ions
1
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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 1998-2001 R.J. Rusay