Atomic Structure

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Atomic Structure

• From Indivisible to Quantum Mechanical Model of
  the Atom

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Quantum mechanical model(Modern Atomic Theory)

• SchrÖdinger
• Heisenberg
• Pauli
• Hund

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Heisenbergs Uncertainty Principle

• Impossible to determine both the position and the
  velocity of an e- in an atom simultaneously with
  great certainty.

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SchrÖdinger

• e- not in neat orbits, but exist in regions
  called orbitals

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Definitions

• Orbital ? region in space where the probability
  of finding an electron is the highest

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Quantum Numbers

• Definition specify the properties of atomic
  orbitals and the properties of electrons in
  orbitals
• There are four quantum numbers

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Quantum Numbers (1)

• Principal Quantum Number, n

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Quantum Numbers

• Principal Quantum Number, n
• Values of n 1,2,3, ?
• Positive integers only!
• Indicates the main energy level occupied by the
  electron

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Quantum Numbers

• Principal Quantum Number, n
• Values of n 1,2,3, ?
• Describes the energy level, orbital size

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Quantum Numbers

• Principal Quantum Number, n
• Values of n 1,2,3, ?
• Describes the energy level, orbital size
• As n increases, orbital size increases.

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Principle Quantum Number

• More than one e- can have the same n value
• These e- are said to be in the same e- shell
• The total number of orbitals that exist in a
  given shell n2

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Orbital Shapes

• For a specific main energy level, the number of
  sublevels possible is equal to n.
• Ex. n2, can have two sublevels.
• A sublevel is assigned a letter
• s , p , d, f , g, h

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Energy Level and Orbitals

• n1, only s orbitals
• n2, s and p orbitals
• n3, s, p, and d orbitals
• n4, s,p,d and f orbitals

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Atomic Orbitals

• Atomic Orbitals are designated by the principal
  quantum number followed by letter of their
  subshell
• Ex. 1s s orbital in 1st main energy level
• Ex. 4d d sublevel in 4th main energy level

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The area where an electron can be found, the
orbital, is defined mathematically, but we can
see it as a specific shape in 3-dimensional space
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Orbital Shapes

• s is spherical.
• One possible orientation.

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z
y
x
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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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1s orbital
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2s orbital
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Orbital Shapes

• p orbital.
• dumbbell shape

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There are three p orbitals
3 possible orientations
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DEGENERATE ORBITALS
The three 2p orbitals are oriented perpendicular t
o each other
All three orbitals are identical of each other
by energy, size and shape.The only difference is
their orientation in space.
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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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z
The three 2p orbitals, 2px, 2py, 2pz
y

• 3p, 4p, 5p, etc have the same shape and number,
  just larger

x
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Orbital Shapes

• d orbital.
• double dumbbell or four-leaf clover
• It has 5 degenerate orbitals
• 5 possible orientations
• The 4d orbitals etcare the same shape, only
  larger

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Orbital Shapes

• f orbital
• It has 7 degenerate orbitals
• 7 possible orientations

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Energy Level and Orbitals

• n1, only s sublevel
• n2, s and p sublevels
• n3, s, p, and d sublevels
• n4, s,p,d and f sublevels

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In the same energy level, energies of orbitals

• s lt p lt d lt f
• (because of the amount of repulsion between
  electrons)

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Quantum Numbers (4)

• Electron Spin Quantum Number,
• ms 1/2, ?1/2)

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• Electron Spin QN
• 1. Relates to the spin states of
• the electrons.
• 2. Electrons are 1 charged and
• are spinning
• 3. The two possible spin directions are called ½
  and ½

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Pauli Exclusion Principle
No 2 e- in an atom can have the same set of four
quantum numbers (n, l, ml, ms ). Therefore, no
atomic orbital can contain more than 2 e-. and
they must have opposite spin.
Wolfgang Pauli
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Sublevels

• There are 4 sublevels(different shaped orbitals)
• s (has 1 orbital)
• p (has 3 orbitals)
• d (has 5 orbitals)
• f (has 7 orbitals)
• Each orbital can hold 2 electrons

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Energy Level (n) Sublevels in Level Orbitals in Sublevel Total of Orbitals in Level
1 s 1 1
2 s 1 4
2 p 3 4
3 s 1 9
3 p 3 9
3 d 5 9
4 s 1 16
4 p 3 16
4 d 5 16
4 f 7 16
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Electron Configurations

• Electron Configurations arrangement of e- in an
  atom
• There is a distinct electron configuration for
  each atom
• There are 3 rules for writing electron
  configurations

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Aufbau Principle

• Aufbau Principle an e- occupies the lowest
  energy orbital that can receive it.

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Aufbau order

ENERGY
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Writing Electron Configurations
of e-
Describes e- location.

• 3p4

Principal Energy Level
Sublevel
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Electron Configuration

• The total of the superscripts must equal the
  atomic number (number of electrons) of that atom.

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Orbital Diagrams

• These diagrams are based on the electron
  configuration.
• In orbital diagrams
• Each orbital (the space in an atom that will hold
  a pair of electrons) is shown.
• The opposite spins of the electron pair is
  indicated.

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Orbital Diagram Rules

• Represent each electron by an arrow
• The direction of the arrow represents the
  electron spin
• Draw an up arrow to show the first electron in
  each orbital.
• Hunds Rule(the principle of multiplicity)
  Distribute the electrons among the orbitals
  within sublevels so as to give the most unshared
  pairs.
• Put one electron in each orbital of a sublevel
  before the second electron appears.

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Hunds Rule

• One electron enters each orbital of equal energy
  (degenerate orbitals)until all the orbitals
  contain one electron with the same spin
  direction
• then they pair up.

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configuration 1s 2s 2px 2py 2pz
H 1s1 ?
He 1s2 ? ?
Li 1s22s1 ? ? ?
Be 1s22s2 ? ? ? ?
B 1s22s22p1 ? ? ? ? ?
C 1s22s22p2 ? ? ? ? ? ?
N 1s22s22p3 ? ? ? ? ? ? ?
O 1s22s22p4 ? ? ? ? ? ? ? ?
F 1s22s22p5 ? ? ? ? ? ? ? ? ?
Ne 1s22s22p6 ? ? ? ? ? ? ? ? ? ?
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Orbital Diagram Examples

• H ?_
• 1s
• Li ?? ?_
• 1s 2s
• B ?? ?? ? __ __
• 1s 2s 2p
• N ?? ?? ? ? ?_
• 1s 2s 2p

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Orbital filling table
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• We can use the previous Noble Gas as an
  abbreviation to indicate filled inner orbitals
• a. Na 1s22s22p63s1 or Ne3s1
• b. Ca Ar4s2
• c. Cl Ne3s23p5
• d. Rb Kr5s1

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Dot Diagram of Valence Electrons

• When two atom collide, and a reaction takes
  place, only the outer electrons interact.
• These outer electrons are referred to as the
  valence electrons. Valence electrons are
  available to be lost, gained, or shared in the
  formation of chemical compounds

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Lewis Dot(electron dot) diagrams

• A way of keeping track of valence electrons.
• Write the symbol.
• Put one dot for each valence electron
• Start at 3 oclock move in a counterclockwise
  direction Video

X
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• Distribute one valence electron at a time
• Do not pair (double up) any electrons until there
  is one electron in each of the four directions
• Pair up electrons once there is one in each of
  the four directions

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The Lewis Dot diagram for Nitrogen

• Nitrogen has 5 valence electrons.
• First we write the symbol.

N

• Then add 1 electron at a time to each side.

• Until they are forced to pair up.