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Electrons, Orbitals and Electron Configurations

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... properties of both particles and waves, and can act as such ... Here's a short-hand method for representing electron configurations. Use the noble gas notation! ... – PowerPoint PPT presentation

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Title: Electrons, Orbitals and Electron Configurations


1
Electrons, Orbitals andElectron Configurations
2
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  • no longer valid)

3
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

4
  • 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

5
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
    _____________

6
  • 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

7
  • 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

8
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

9
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

10
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
  • ________________________________________________
    ___________________________________

11
Representing Electron Configuration
  • Orbital diagram

12
  • Example Carbon
  • C
  • 1s 2s
    2p

13
Representing Electron Configuration
  • Electron configuration notation
  • For example Carbon
  • C 1s2 2s2 2p2

14
z
y
The 3 axes represent 3-dimensional space
x
15
z
y
For this presentation, the nucleus of the atom is
at the center of the three axes.
x
16
The 1s orbital is a sphere, centered around the
nucleus
17
The 2s orbital is also a sphere.
18
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.
19
Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
The s orbitals are spheres
20
There are three 2p orbitals
21
The three 2p orbitals are oriented perpendicular t
o each other
22
z
This is one 2p orbital (2py)
y
x
23
z
another 2p orbital (2px)
y
x
24
z
the third 2p orbital (2pz)
y
x
25
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)
26
once the 1s orbital is filled,
27
the 2s orbital begins to fill around the 1s
orbital
28
once the 2s orbital is filled,
29
the 2p orbitals begin to fill
30
each 2p orbital intersects the 2s orbital and the
1s orbital
31
each 2p orbital gets one electron before pairing
begins
32
once each 2p orbital is filled with a pair of
electrons, then
33
the 3s orbital gets the next two electrons
34
the 3s electrons have a higher energy than 1s,
2s, or 2p electrons,
35
so 3s electrons are generally found further from
the nucleus than 1s, 2s, or 2p electrons
36
Try these
  • Nitrogen
  • Fluorine

37
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

38
Try these
  • Magnesium
  • Chlorine

39
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
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