Quantum Mechanical Model

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New unit !

• Quantum Mechanical Model
• and Periodicity

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• DeBroglie ? duality
• treated the electron as a function of a wave
  (Bohr treated as a particle)
• If waves of energy have some properties of
  particles, perhaps particles of matter have some
  properties of waves.
• Combined Emc2 with Eh x nu
• Distinction between both particle and wave
  disappears at the atomic level
• Differs from Bohr model in several ways
• 2 of particular note
• The kinetic energy of an electron is inversely
  related to the volume of the region to which it
  is confined (more common electrostatic energy
  decreases as kinetic energy increases creating a
  balance )
• It is impossible to specify the precise position
  of an electron in an atom at a given instant (the
  best that can be done is estimate the
  probability of finding an electron in a
  particular region
• Schrodinger
• Wave function of electron
• Certain allowed amounts of energy due to the
  allowed wave-like motion of an electron
• Electron cloud

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Quantum Mechanical ModelEach electron has its
own region within the atom and has a number
designation describing that region

• Principle quantum number (n)
• main energy level or shell
• represented by whole number
  integers (1, 2, 3 ...the
  period number on the p-table)
• number indicates the distance from the
  nucleus (the gt the pqn the farther the
  electrons are from the nucleus)
• specifies the size of the ORBITAL

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Sublevels, sublevels, sublevels

• 2. Azimuthal quantum
• represented by the letter l
• shape of the electron cloud
• the of sublevels is equal to the value of the
  pqn
• (pqn 2, then there are 2 sublevels)

l integer from 0 to (n-1) l 0, 1, 2, 3 Ex.
1 1 0 ( representing the s sublevel)
Sublevels are? s..p..d..f..g..h..so on
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• Atomic Orbital Shapes and Sizes
• Names derived from the characteristics of their
  spectroscopic lines sharp, principle, diffuse,
  and fundamental
• s
• p
• d
• f
• and so ong, h,

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ORBITALS http//chemed.chem.wisc.edu/chempaths/Gen
Chem-Textbook/Orbitals-896.html

• Within sublevels each electron pair has a
  different place in space.
• This space is called an orbital.

Max. 2 electrons per orbital
ml - l to l
s-sublevel----1 orbital----- ml 0 p-sublevel
----3 orbitals ----- ml -1, 0, 1 d-sublevel
----5 orbitals ----- ml -2, -1, 0, 1,
2 f-sublevel ----7 orbitals ----- ml -3, -2,
-1, 0, 1, 2, 3
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Electrons in the same region?
4. Spin Quantum Number (ms) NOT a property
of the orbital describes a property of the
electron itself indicates the direction of the
electron spin ms 1/2 or -1/2
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Electron Configuration
the distribution of electrons within the
orbitals of an elements atoms
determines behavior and chemical properties
and reactivity of the elements
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Electron Configurations

• Orbital notation
• main energy level (pqn, 1, 2, 3 etc)
• letter sublevel (s, p, d, f)
• orbital
• electrons

3s
2p
2p
2p
Starting order of energy level with sublevel and
orbital
2s
1s
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Here electron, come on boy!

• Aufbau principle
• electrons are added one at a time
• you begin with the lowest energy
• you add electrons until all electrons are
  accounted for

• Pauli exclusion principle
• an orbital can hold a maximum of 2 electrons
• paired and unpaired

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More assigning of electrons

• Hunds rule
• all orbitals within a sublevel must have at
  least one electron before a paired electron can
  be used
• It doesnt matter which one gets an electron
  first, but
• 1. Each electron MUST have the SAME SPIN as the
  others in unfilled orbitals! (up or down)
• 2. NO electron pairs are allowed until every
  orbital in that sublevel has one electron!

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Orbital Diagram
Energy
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Electron Promotion
A d subshell is more stable when it is EXACTLY
1/2 FULL (5 electrons), or EXACTLY FULL! (10
electrons)! The same is true for f subshells!
(7 or 14 electrons) When a d
is ONE electron short of 1/2 full or full It
PROMOTES one electron from the nearest s
subshell!
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Configuration notation (aka REGULAR NOTATION)

• With configuration notation, the concept of
  orbital notation is still usedBUT
• The orbitals are no longer represented by boxes
• The energy level and the sublevel are still
  used (1s, 2s 2p and so on)BUT
• The arrows representing the electrons are not
  used
• The number of electrons is still important AND
• The number of electrons are written as
  superscripts above the sublevel designation
• Example Sodium, Na (11 electrons)
• ? 1s2 2s2 2p6 3s1

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Short hand notation

• With shorthand notation, the same technique as
  configuration notation is used.
• The difference is
• all of the electrons to the previous row NOBLE
  GAS are accounted for
• the configuration continues from the end of the
  noble gas row and picks up at the beginning of
  the next energy level
• the technique is to put the noble gas element
  symbol in brackets Ex. Ar 18
• the configuration notation picks up and continues
  until all the electrons are accounted for
• Ex. Cu29 ? Ar18 4s2 3d9

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d and f Subshells Fill LATE

• d subshells fill 1 shell behind!
• 3d fills after 4s
• 4d fills after 5s

• f subshells fill 2 shells behind! MORE complex!
• The first f subshell is in the 4th shell (4f)
• 4f fills after 6s! (then comes 5d, and then 6p)
• 5f fills after 7s, (then comes 6d, and then 7p)
• Just follow the elements in order!!

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Electron Promotion
Example Silver (Ag) 1s2, 2s2, 2p6, 3s2, 3p6,
4s2, 3d10, 4p6, 5s2, 4d9
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9
2
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4d9 1 short of full!
Silver (Ag) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10,
4p6, 5s1, 4d10
Silver is now more stable with a full4d
subshell! (4d10)
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Electron Promotion
Remember! One s electron will promote to the
nearest d or f subshell if that d or f
is one electron short of being full or 1/2
full! Watch for d 4, d 9, f 6 or f 13!
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• Practice quantum s
• Consider the following sets of quantum numbers
  a) 3, 1, 0, 1/2 b) 1, 1, 0, -1/2 c) 2, 0,
  0, 1/2 d) 4, 3, 2, 1/2
• which ones are valid
• If valid, identify the orbital involved

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VALENCE ELECTRONS

• The electrons in the outermost energy level are
  called valence electrons.
• Valence electrons are the ones that cause
  chemical properties and reactions
• Look for the highest n (principle energy
  level), such as 3s, or 4p, etc.
• Valence electrons will ALWAYS be in s or p
  subshells!

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Lewis Dot Structures
This is EASY! The dots placed around the symbol
of an element represent ONLY THE OUTSIDE
ELECTRONS! These outside electrons are called
the valence electrons! Remember, ONLY s AND
p SUBSHELLS ARE ON THE OUTSIDE!!! This means
that the total number of dots around a symbol can
NEVER exceed 8!! (s 2, p 6) This is called
the OCTET RULE!
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Lewis Dot Diagrams

• A Lewis dot diagram illustrates valence electrons
  as dots around the chemical symbol of an element.

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Lewis Dot Diagrams

• Each dot represents one valence electron.
• In the dot diagram, the elements symbol
  represents the core of the atomthe nucleus plus
  all the inner electrons.

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Lewis Dot Diagrams Represent Valence Electrons
The dots are written around an imaginary box
surrounding the element symbol, up to a maximum
of eight! (no pairs before 5!) (the dots may
start on any side)
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OK WHY does 4s fill before 3d?
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3d subshell
Farther out than 2nd shell, but all 3 an equal
distance from the nucleus.
3p subshell
3s subshell
3rd shell
Farther out than 1st shell, but both an equal
distance from the nucleus.
2p subshell
2s subshell
2nd shell
Closest to the nucleus
1s subshell
1st shell
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Note that, even though the 4th shell is farther
out than the 3rd shell, the energy of 4s is LESS
than 3d!
4th shell
4f subshell
Farther out than 3rd shell, but all 4 an equal
distance from the nucleus.
4d subshell
4p subshell
3d subshell
3rd shell
4s subshell
Farther out than 2nd shell, but all 3 an equal
distance from the nucleus.
3p subshell
3s subshell
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