The Atom

1
The Atom

• Chapter 2

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Daltons Atomic Theory (1803)
Do you know which of these statements are still
valid?

• Elements are made up of atoms that are
  indivisible and indestructible.
• All atoms of an element have the same mass. No
  two different elements have the same mass.
• Compounds consist of small whole number ratios of
  elements.
• Elements are not changed during chemical reaction.

False!
False!
True!
True!
3
Models of the Atom
4
1903 Thomson The plum pudding model
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Rutherfords Alpha Scattering Experiment
Movie
Movie
6
The Results!
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Rutherford model
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Subatomic Particles
Particle symbol location charge mass Electron e-
orbital -1 1/1836 Proton p nucleus 1 1 Neu
tron n nucleus 0 1
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Describing Individual Atoms
Example
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Lets see if you have it!

• Fill in the blanks
• Symbol neutrons protons electrons
• 60Co
• 81Br
• 36 29 27

27
27
33
-
35
36
46
65Cu2
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Isotopes
Stable?

• Isotopes are atoms with the same number of
  protons but different numbers of neutrons.
• Same element, different mass.
• Some isotopes are stable, others are not.
• The masses on the periodic table are weighted
  averages.
• Isotopes of hydrogen and carbon.

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Chlorine

• Chlorine is 75 chlorine-35 and 25 chlorine-37.
  What is the average mass?

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Wave Nature of Light
Wavelength the distance light travels to
complete one cycle. Frequency the number of
wave cycles in one second.
Red light
Which wave has the higher frequency?
UV
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Radiant Energy Spectrum
High energy, short waves
Low energy, long waves
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Bohr Model of Atom (Year 1913)
nucleus
Energy Levels
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What was the evidence?
link
Discontinuous line spectra of atoms!
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Final Statements on the Bohr model
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The electron as a wave

• Einstein, Light, a wave, can have particle like
  properties
• De Brolie, particles, like electrons, can have
  wave-like properties
• Scrödinger, Came up with an equation that
  describes an electron

The Players
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The outcome

• n, principle quantum number. Correlates with
  shell of Bohr model
• l, subshell. Correlates with type of orbital, s
  p d or f.
• ml, orientation. px, py or pz.
• s, spin. ?or ?

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Energy Levels and Subshells

• Each energy level is divided into sublevels,
  often called subshells.
• Types of subshells s, p, d, f
• Number of subshells in an energy level depends on
  the energy level.

E. Level 1 2 3
4 Subshell s s,p s,p,d s,p,d,f
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Subshells and Orbitals

• Electrons exist in orbitals.
• Most probable location for finding an electron.
• The number of orbitals depends on the subshell
• 2 electrons per orbital
• s orbitals come in groups of 1
• p orbitals come in groups of 3
• d orbitals come in groups of 5

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S orbitals

• S orbitals are spherical

1s
3s
2s
How does a 1s orbital differ from a 3s orbital?
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p Orbitals
How many electrons fit in a 2 p orbital?
pz
py
px
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The first shell only has an s orbital The second
shell has s p orbitals The third shell has s, p
d orbitals
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Orbitals in the third shell
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Electron Configurations
(Shell-subshell notation)
Lets investigate Electron Housing!
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Electron Configuration - N
5p
5s
4p
3d
EPOT
4s
3p
3s
2p
2s
Each arrow represents an electron 1s2 2s2 2p3
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Electron Configuration - Na
5p
5s
4p
3d
EPOT
4s
3p
3s
2p
2s
Each arrow represents an electron 1s2 2s2 2p6
3s1
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Electron Configuration - V
3d
EPOT
4s
3p
3s
2p
2s
Each arrow represents an electron 1s2 2s2 2p6
3s2 3p6 4s2 3d3
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An Easier Way
n energy level period number
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Electron Configuration Al
1s2 2s2 2p6 3s2 3p1
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Electron Configuration - Co
1s2 2s2 2p6 3s2 3p6 4s2 3d7
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Electron Configuration - Sr
1s2 2s2 2p6 3s2 3p6 4s2 3d104p65s2