Electron Configuration

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Electron Configuration

• Chapter 4
• Quantum numbers,
• describe the orbitals in which electrons can be
  found.

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Bohr was wrong!!

• Electrons spend time around the nucleus but NOT
  in nice neat circular orbits.

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Where are the electrons?

• We cannot know exactly where the electrons are.
• We can only know with some degree of certainty
  where it is.
• Quantum numbers describe where the electron may
  be found.
• Quantum numbers are the electrons address.

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Dual nature of light and matter

• Energy travels in packets of energy, sort of like
  steps.
• When an electron is excited to a higher energy
  level, it emits light when it returns to its
  original orbit.
• Law of Conservation of Energy.

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principle quantum number (n)

• Describes the size of the orbital.
• Referred to as the energy level.

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The angular quantum number (l)

• (l) describes the shape of the orbital.
• Spherical , s, (l 0)
• Polar, p. (l 1)
• Cloverleaf ,d, (l 2)
• They can even take on more complex shapes as the
  value of the angular quantum number becomes
  larger.

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magnetic quantum number

• Magnetic quantum number (m)
• Describes the orientation in space of a
  particular orbital. X,Y, Z axis
• Named magnetic quantum number because the effect
  of different orientations of orbitals was first
  observed in the presence of a magnetic field.

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Spin

• Each orbital shape may hold two electrons.
• These two electrons have opposite spins.
• Designated as ½ - ½

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Da Rules

• The principle Quantum Number is an integer
  greater than or equal to 1.
• The angular quantum number (l) can be any integer
  between 0 and n - 1. If n 3, for example, l can
  be either 0, 1, or 2.
• The magnetic quantum number (m) can be any
  integer between -l and l. If l 2, m can be
  either -2, -1, 0, 1, or 2.
• Spin is ½ - ½

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Shells and Subshells of Orbitals

• Orbitals that have the same value of the
  principle quantum number form a shell. Orbitals
  within a shell are divided into subshells that
  have the same value of the angular quantum
  number. Chemists describe the shell and subshell
  in which an orbital belongs with a two-character
  code such as 2p or 4f. The first character
  indicates the shell (n 2 or n 4).

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Shells and Subshells of Orbitals

• The second character identifies the subshell. By
  convention, the following lowercase letters are
  used to indicate different subshells.

s l 0
p l 1
d l 2
f l 3
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The d orbitals
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Electron Configuration

• H 1s1

• A hydrogen atom has only one electron.
• The lowest energy orbital is the 1s orbital.
• This is indicated by writing a superscript "1"
  after the symbol for the orbital.

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Aufbau principle

• Each electron is added to the lowest energy
  orbital available.
• Up to two electrons may be added to each orbital.

• He 1s2
• Li 1s2 2s1
• Be 1s2 2s2
• B 1s2 2s2 2p1
• C ????????
• C 1s2 2s2 2p2

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But

• After all not all the orbitals are filled in
  Energy Level order!!

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Hund's rules can be summarized as follows.

• One electron is added to each of the degenerate
  orbitals in a subshell before two electrons are
  added to any orbital in the subshell.
• Electrons are added to a subshell with the same
  value of the spin quantum number until each
  orbital in the subshell has at least one
  electron.
• Filling the Bus!

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Pauli Exclusion Principle

• No two electron in an atom may have the same set
  of quantum numbers.
• This is Pauli. Dont Mess with Pauli!