Transcript 3.4_Orbitals_and_Electron_Configuration

Quantum Mechanical Model of
the Atom
Orbitals and Electron
Configuration
Mrs. Hayes
Chemistry
Quantum Mechanical Model
Orbitals and the Quantum
Mechanical Model of the Atom
• Since we know that Bohr’s model of
hydrogen will not work for all atoms, we
need another way to predict where
electrons are located.
• We use “orbitals” not “orbits” to make this
prediction.
s, p, d orbital shapes
Quantum Mechanical Model
Energy Levels
• The energy levels in an atom
are sort of like rungs of a ladder.
• The more energy an electron
has, the farther away from the
nucleus it usually will be.
• The energy levels are not
evenly spaced. They get closer
together as you travel farther
away.
• To move from one “rung” to
another requires a “quantum”
of energy.
e- Movement is Based on 3 Factors
• Their energies.
• Their orientation in space.
• How wildly they swing about in their path
(some swing back and forth like waving
your arms instead of making a full circle).
Quantum Numbers
• Describe the locations of the e-’s around
the nucleus.
• Quantum #’s are sort of like a home
address for the electron.
Quantum Numbers
• Principal Q. #: Describes the distance that the electron
is from the nucleus. The bigger the number, the farther
away the electron is. Example: (1=closest, 2, 3,
4...farther away)
• Magnetic Q. #: tells how many orientations in 3-D there
are about the nucleus for each orbital shape.
• s = 1 orientation
• p= 3 orientations... (x, y, and z)
• d= 5 orientations
• f= 7 orientations
Quantum Numbers
• Angular Momentum Q. #: Describes the shape of the
electron’s path around the nucleus with a letter: (s, p, d,
& f) These are sometimes called “sublevels”.
• Spin Q. #: describes how the electron in an orientation
is spinning around the nucleus. Some like to imagine it
spinning “clockwise” and “counterclockwise”.
•
The spin is represented as an arrow in the direction of
the spin.
Electron Configurations
• “Configuration” means the arrangement of
the parts of something.
• Electron configuration is the arrangement
of electrons in space around the nucleus.
Rules for e- configurations
• Rule #1 (Aufbau Principle):
Electrons fill lowest
energy orbitals first.
• Rule #2: Only 2 electrons can fit into each
orientation.
• Rule #3 (Pauli Exclusion Principle):
Electrons in
the same orientation have opposite spin.
• Rule #4 (Hund’s Rule):
□
“Monopoly rule”--->
Every “ ” in an orbital shape gets an electron
before any orientation gets a second e-.
Electron Configurations
• The orientations are represented with a line or a
box.
• Examples: ___ This means a spherical orbital at
a distance of 1s, “1” (close) to the nucleus. This
orbital is centered about the x, y, and z axis.
•□ □ □
This represents an ellipsoid
orbital with its 4p with 3 possible orientations at
a distance of “4 ”from the nucleus
Electron Configuration Pattern
What do the Numbers and Letters
Represent?
• The large numbers represent the main
energy levels and are determined by the
electrons’ average distance from the
nucleus.
• The letters are the sublevels in which the
electrons are found (s, p, d, f)
• Each main energy level has a certain
number of sublevels.
How to Use the Configuration
• We move across the periodic table from left
to right just like we read a book.
• Let’s take the element Lithium (Li, 3)
• Lithium has 3 protons, so a neutral atom of Li
will have 3 electrons
• We need space for 3 electrons:
– 1s2, 2s1
• There are 2 electrons in the first sublevel, and
one electron in the second sublevel.
• 2 + 1 = 3…that’s it!
Orbital Diagrams
We can DRAW the Configuration, too.
2s orbital can hold 2
electrons, but we have only
one to place there.
1s2
Lithium
2s1
You must fill the first sublevel
before going to the next one.
Electrons have opposite
“spins” in an orbital, so we
have the arrows going in the
opposite direction.
Let’s Try Fluorine…
• Fluorine has an atomic number of 9, so it
has 9 electrons in a neutral atom.
• 1s2,2s2, 2p5
The 2p orbital can hold 6 electrons, but we only
have five to place there.
1s2
2s2
2p5
What About Arsenic?
• Atomic number = 33, so 33 electrons
• Fill up the s orbitals first
• Fill up the sublevels until we get to
4p…then we have only three left there.
4p3
3d10
4s2
3p6
3s2
2p6
2s2
1s2
Aufbau principle
Pauli says
no two
electrons in
orbital can
be alike, so
opposite
spins.
Hund’s
Rule. Each
orbital of
equal
energy must
be occupied
before a
second
electron can
enter. All
single
electrons
have the
same spin.
We Also Have ShorthandThe “Noble Gas Configuration”
• Use the nearest noble gas BEFORE the
element to replace the sublevel orbitals in
your configuration.
– Example for Magnesium:
• Neon, 3s2
• Neon replaces 1s2, 2s2, and 2p6