Electrons, Orbitals and Electron Configurations

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Electrons, Orbitals andElectron Configurations
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DeBroglie

• One part of Bohrs model was incorrectthe fact
  that electrons __________move around the nucleus
  in circular orbits
• Along came _____________he
• stated that all moving particles
• have ___________ characteristics
• (so the circular orbit theory is
• no longer valid)

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Quantum Mechanical Model

• Electrons have properties of both particles and
  waves, and can act as such
• Like the Bohr model, the quantum mechanical model
  of the atom restricts the energy of electrons to
  certain valuesbut it does not define an exact
  path an electron takes around the nucleus

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• A __________-dimensional region around the
  nucleus called the _____________________
  describes the electrons probable location
• The electron __________ is more dense around the
  positive nucleus indicating the electrons
  probable location

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Hydrogens Atomic Orbitals

• Because the atomic orbital has no definite
  boundary, the orbital does not have an exactly
  defined size
• To overcome this uncertainty, chemists
  arbitrarily draw an orbitals surface to contain
  90 of the electrons total probability
  distribution
• There are _____________________________ (n) that
  indicate the relative sizes and energies of
  atomic orbitals.
• As n increases, the orbital becomes ___________,
  the electron spends more time farther away from
  the nucleus, and the atoms energy level
  _____________

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• We will now discuss how the electrons are
  arranged in atomic orbitals of atoms having more
  than one electron
• This arrangement follows a few very specific
  rules
• The aufbau principle
• Pauli exclusion principle
• Hunds rule

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• The arrangement of electrons in an atom is called
  the atoms _______________________
• Low energy systems are ______ stable than
  high-energy systems so electrons tend to assume
  the arrangement that gives the atom the lowest
  possible energythis is called the elements
  ground-state electron configuration

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The Aufbau Principle

• The Aufbau principle states that each electron
  occupies the ___________ energy orbital available
• You need to know the sequence of atomic orbitals
  from lowest energy to highest energy
• The energy sublevels
• are filled
• in a specific
• order that is shown
• by the arrow diagram

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The Pauli exclusion principle

• Each electron in an atom has an associated spin,
  similar to the way a top spins on its axis
• Like the top, an electron can spin in only one of
  two directions
• An arrow pointing up indicates an electron
  spinning in one direction and an arrow pointing
  down indicates an electron spinning in the
  opposite direction
• The Pauli exclusion principle states that a
  maximum of two electrons may occupy a single
  atomic orbital, but only if the electrons have
  opposite spins
• An atomic orbital containing paired electrons
  with opposite spins is written as

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Hunds rule

• Negatively charged electrons repel each other and
  this has an impact on the distribution of
  electrons in equal energy orbitals
• For example
• all three 2p orbitals are of equal energy
• 2p
• ________________________________________________
  ___________________________________

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Representing Electron Configuration

• Orbital diagram

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• Example Carbon
• C
  
• 1s 2s
  2p

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Representing Electron Configuration

• Electron configuration notation
• For example Carbon
• C 1s2 2s2 2p2

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z
y
The 3 axes represent 3-dimensional space
x
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z
y
For this presentation, the nucleus of the atom is
at the center of the three axes.
x
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The 1s orbital is a sphere, centered around the
nucleus
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The 2s orbital is also a sphere.
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The 2s electrons have a higher energy than the
1s electrons. Therefore, the 2s electrons are
generally more distant from the nucleus, making
the 2s orbital larger than the 1s orbital.
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
The s orbitals are spheres
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There are three 2p orbitals
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The three 2p orbitals are oriented perpendicular t
o each other
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z
This is one 2p orbital (2py)
y
x
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z
another 2p orbital (2px)
y
x
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z
the third 2p orbital (2pz)
y
x
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
This is the shape of p orbitals (dumbbell shaped)
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once the 1s orbital is filled,
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the 2s orbital begins to fill around the 1s
orbital
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once the 2s orbital is filled,
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the 2p orbitals begin to fill
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each 2p orbital intersects the 2s orbital and the
1s orbital
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each 2p orbital gets one electron before pairing
begins
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once each 2p orbital is filled with a pair of
electrons, then
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the 3s orbital gets the next two electrons
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the 3s electrons have a higher energy than 1s,
2s, or 2p electrons,
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so 3s electrons are generally found further from
the nucleus than 1s, 2s, or 2p electrons
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Try these

• Nitrogen
• Fluorine

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Heres a short-hand method for representing
electron configurations

• Use the noble gas notation!
• Neon
• Sodium
• Using noble gas notation, sodiums configuration
  can be shortened to the form

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Try these

• Magnesium
• Chlorine

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Valence Electrons (revisited)

• Only certain electrons, called ____________
  electrons, determine the chemical properties of
  an element
• Valence electrons are electrons in the atoms
  outermost orbitals
• For example
• Sulfur has 16 electrons only six of which occupy
  the outermost 3s and 3p orbitalstherefore,
  sulfur has 6 valence electrons
• S Ne3s2 3p4
• Cesium has 55 electrons, but only one valence
  electron
• Cs Xe6s1