Download Atomic theory.notebook

Atomic theory.notebook
September 11, 2012
Early Theories of Matter
Atomic Structure
Chapter 4
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• Greek philosophers (Empedocles 450 B.C.)
• air, water, earth, fire
• Democritos (420 B.C.)
• atoms
• John Dalton (1776­1884)
• All matter made of atoms.
• Atoms of same element are identical & vice versa.
• Atoms cannot be created, divided, or destroyed.
• Atoms combine in whole # ratios to make compounds.
• Atoms are separated, combined, or rearranged in chemical reactions.
Aug 30­3:53 PM
Aug 30­3:53 PM
Defining the Atom
Subatomic Particles
What is an atom?
Size of atom
1 cm ≈ 200 000 000 atoms
Scanning tunneling microscope
• Discovering the electron
• William Crookes: cathode ray tubes
• Stream of charged particles
• Carries a negative charge
Si atoms on face of a crystal
Aug 30­3:53 PM
electron cont…
• J.J. Thomson – discovered electron (e­)
• mass of e­ = 9.11 × 10­28 g
• Plum pudding model (1897)
Aug 30­3:53 PM
The Nuclear Atom
• Rutherford – discovered nucleus (1911)
• gold foil experiment
• small positive core
• core contains most of atom’s mass
• mostly empty space
• Robert Millikan – determined charge of electron
• 1.60 × 10­19 coulombs Aug 30­3:53 PM
Aug 30­3:53 PM
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Atomic theory.notebook
September 11, 2012
Bohr Model of the Atom
Discovering protons & neutrons
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Proton (1919)
Discovered by Rutherford
Positively charged; in nucleus
Neutron (1932)
discovered by Chadwick
Neutral; in nucleus
• Neils Bohr – proposed quantum model of the atom
• Electrons move about the atom in circular paths of specific energies
• Termed these paths energy levels
• Later determined to be fundamentally incorrect
Nuclear Model of the Atom
Aug 30­3:53 PM
Aug 30­3:53 PM
Quantum Mechanical Model •
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Summarizing the Atom
Louis de Broglie
Wave­particle duality
Erwin Schrödinger
Electrons treated as waves
Electrons exist in “clouds” around the nucleus
1­
0
1.67x10­24
Aug 30­3:53 PM
Aug 31­9:59 AM
1/1840
9.11x10­28
no
p+
1
1+
1
Aug 30­3:53 PM
Atomic Number (Z)
• Number of protons in the atom
• Since atoms are neutral, number of protons
and number of electrons are the same (if they
are not equal, then have ion, cation, anion)
• Therefore,
Atomic number = # protons = # electrons
1.67x10­24
e­
Mass Number
• Mass number is the sum of the protons and
neutrons in an atom
• Mass number = p+ + n0
p+
n0
e­
Mass #
11
12
11
23
Potassium 19
20
19
39
Bromine
45
35
80
Sodium
35
Aug 31­9:59 AM
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Atomic theory.notebook
September 11, 2012
THE STRUCTURE OF THE ATOM
To calculate the composition of an atom
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Proton
Neucleons
Neutron
A
mass number
Na SYMBOL
X
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Zatomic mass
Electron
<http://education.jlab.org/qa/atom_model_03.gif>
Number of protons + neutrons = A
The mass of the atom is concentrated in the nucleus.
The volume of the atom is determined by the space that the electrons move in, around the nucleus
Number of protons = Z
Number of electrons in neutral atom = Z
Number of neutrons = A ­ Z
Nov 28­11:16 AM
Nov 28­12:50 PM
Isotopes
• Isotopes are atoms of the same element that
have different mass numbers due to a different
number of neutrons
• Same number of protons, but different
number of neutrons
• # neutrons = mass number – atomic number
Nov 28­02:06 PM
Aug 31­9:59 AM
Atomic Mass
• Atomic mass is the average of all the isotopes of that
element
Carbon – 12.011
Isotope
Protons
Electrons
Neutrons
Hydrogen – 1
(protium)
1
1
0
Hydrogen – 2
(deuterium)
1
1
1
Hydrogen – 3
(tritium)
1
1
2
Aug 31­9:59 AM
Composition
% in nature
of nucleus
Isotope
Symbol
Carbon – 12
12C
6 protons
6 neutrons
98.89%
Carbon – 13
13C
6 protons
7 neutrons
1.11%
Carbon - 14
14C
6 protons
8 neutrons
<0.01%
Aug 31­9:59 AM
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Atomic theory.notebook
Nuclear Symbol
235
92
September 11, 2012
Calculating Atomic Mass
Example on page 103
• Chlorine – 37
• Chlorine – 35
• Atomic mass: 34.969 amu • Atomic mass: 36.966 amu
• % abundance: 24.230%
• % abundance: 75.770%
• Mass contribution:
• Mass contribution:
(36.966 amu)(24.230%) = 8.957
(34.969 amu)(75.770%) =
amu
26.496 amu
• Atomic mass of Chlorine = 26.496 amu + 8.957 amu =
35.453 amu
Aug 31­9:59 AM
Aug 31­9:59 AM
Summarizing the Atom
• Atoms are electrically neutral (p+ = e­)
• e­ held in orbit by attraction to nucleus
• n0 present to break up p+ repulsion
Aug 30­3:53 PM
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