Download The Atom

The Atom
By: M. Silverman
Structure
The Proton
• Location: Nucleus
• Charge: Positive (+)
• Responsible for identity of atom and
physical properties.
+
Neutron
• Location: Nucleus
• Charge: Neutral (0)
• Responsible for nuclear properties
(stability)
0
Electron
• Location: Electron Cloud
• Charge: Negative (-)
• Responsible for chemical properties
-
JJ Thomson
1897
• Discovered
charge to mass
ratio of electrons
(=1.759 x 108
coulombs/gram)
Early cathode ray tube
Modern cathode ray tube
Ernest Rutherford
1898
• Determined the atom
has small, dense
nucleus surrounded by
electrons and mostly
empty space.
Nucleus
Electron cloud
R.A. Millikan
1909
• Oil drop experiment determined the
charge (e=1.602 x 10 -19 coulomb)
and the mass (m = 9.11 x 10 -28
gram) of an electron.
James Chadwick
1932
• Using alpha particles discovered
a neutral atomic particle with a
mass close to a proton. Thus, he
discovered the neutron.
Dalton’s Atomic Theory
1) All elements are composed of atoms.
2) Atoms of one element are identical and
different from those of any other element.
3) Atoms combine in whole number ratios to
form compounds.
4) Chemical reactions rearrange atoms, but
do not change them.
Atoms and Elements
Atomic Number (Z)
• Equals number of protons in the atom.
• Functions as an ID number.
• Read directly off the periodic table.
What is the atomic number of this
Element? What element is it?
56, Barium
Atomic Weight
• More correctly: Average Atomic Mass (Ar)
• Read directly off periodic table
• Rounded off, gives Mass number of most
common isotope.
What is the atomic mass of this
Element?
137.3 amu
Mass Number (A)
• Found by adding protons + neutrons
• Is for an individual atom, not an average.
What is the mass number of
this isotope of Barium?
56 + 81 = 137 amu
Isotopes
• Varying forms of an element with different
numbers of neutrons and thus, different
mass numbers.
Barium - 137
Many larger Isotopes are
Unstable = radioactive
Unbalanced ratios of protons to neutrons also make
the nucleus unstable.
Nuclear Fission
Mass Notation
• A way of representing isotopes by putting
the mass number to the upper left of the
symbol and optionally, the atomic number
on the bottom left.
Write the mass notation
for Carbon - 12 and
Carbon – 14.
12
6
Sometimes E is used in place of X.
C
14
6
C
Summary
Rules for Atoms:
•
Number of Protons = Atomic number
p+ = Z
• Electrons = Protons in a neutral atom
e- = p+
• Average atomic mass rounded off equals mass number
of most common isotope
AM rounded off = A
• Neutrons = mass number – atomic number
no = A - Z
Bohr Diagrams
•
•
•
•
Named for Niels Bohr.
Place protons and neutrons in center.
Place electrons around nucleus in shells.
Electron energy levels have limits to what
they can hold.
•
Electron energy levels maximum numbers:
1. 2 e2. 8 e3. 18 e4-7. 32 e-
What element is drawn here?
F
Niels Bohr
Who’s hanging out with
Niels here???
Next:
1. Calculating Average Atomic Mass
2. Nuclear Chemistry
3. Waves, electrons, light, and Quantum
Theory!!!