electron configuration revised by ferguson fall 2014
TRANSCRIPT
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Electron Configuration
Revised by Ferguson
Fall 2014
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How do the chemical properties arise from the structure of atoms?
pages144 ->
• Our first understanding of the arrangement of electrons around the nucleus began in 1920, by Neils Bohr, and is called the Quantum Theory.
• The quantum theory provides insight into why some atoms tend to “gain” electrons and other atoms “donate” electrons to form ions in chemical bonds.
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What is a “quantum” state?• a specific combination of values of
variables such as energy and position that is allowed by quantum theory.
• Electrons are grouped into different “quantum states” as a way to describe the electron arrangement around a nucleus of an atom.
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• Quantum-Mechanical Model of the Atom–Describes the probability that the electron
will be in a certain region of space at a given instant.
–Orbitals are regions of different energies where the electrons can be found.
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• The quantum-mechanical model uses 3 quantum numbers to describe an orbital: –The principal quantum number (n)
•Can be any positive integer
(n=1, n=2, n=3, etc.)•Describes the energy level
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– The angular momentum quantum number (l)Lowercase cursive
L• Can have values from 0 to (n–1)• Defines the shape of the orbital
– The magnetic quantum number (ml)
• Can have integer values between – l and + l • Describes the orientation of the orbital in space
Value of l 0 1 2 3
Orbital shape s p d f
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Value of n
Possible values of l
Subshell possible values of ml
# of orbitals in subshell
1 0 1s 0 1
2 0 2s 0 1
1 2p -1, 0, 1 3
3 0 3s 0 1
1 3p -1, 0, 1 3
2 3d -2, -1, 0, 1, 2 5
4 0 4s 0 1
1 4p -1, 0, 1 3
2 4d -2, -1, 0, 1, 2 5
3 4f -3,-2, -1, 0, 1, 2,3 7
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Orbitals• Orbitals hold electrons, and show the
area in which the electrons can be found.
• “s” orbitals can hold 2 electrons• “p” orbitals can hold 6 electrons• “d” orbitals can hold 10 electrons• “f” orbitals can hold 14 electrons
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Quantum States and Orbitals• There are 4 shapes associated with
quantum states: s, p, d, and f.
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s orbitals
• Have a spherical shape.
• There is one orbital in each s subshell.
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p orbitals• Dumbbell shaped orbitals• Each p subshell contains 3 orbitals.• Each of the 3 orbitals is oriented along a different
axis (x, y, or z)
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d orbitals• Each d sublevel contains 5 orbitals.• 4 of the 5 orbitals have a four-leaf clover
shape. The dz2 orbital has lobes on the z
axis and a “doughnut” shape in the x-y plane.
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f orbitals• An f sublevel will contain 7 orbitals
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Electron Configurations• Electron configuration = a
description of which orbitals contain electrons for a particular atom.
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• All orbitals in the same subshell are said to be degenerate, meaning that they have the same energy. (i.e. the 3 orbitals in the 2p sublevel each have the same energy).
• A maximum of 2 electrons can be located in a given orbital.
Subshell # of orbital Max # of Electrons
s 1 2
p 3 6
d 5 10
f 7 14
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Finding Electron Configuration:
• The complete list of orbitals and the order in which they fill for all of the currently discovered elements is:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Aufbau Principle: orbitals are filled in order of increasing energy (lowest energy orbitals filled first).
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• The fourth quantum number– The magnetic spin quantum number (ms)
– Can have a value of either + ½ or – ½ – Represents the electron’s spin about its axis, which
can generate a magnetic field in two possible directions.
• The Pauli Exclusion Principle– No two electrons in an atom can have the same
quantum numbers. – Therefore two electrons found in the same orbital will
have opposite spins (+ ½ and – ½)
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How to find electron configuration:
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Hund's rule of maximum multiplicity
• When more than one orbital of equal energies are available then the electrons will first occupy these orbitals separately with parallel spins.
• The pairing of electrons will start only after all the orbitals of a given sub level are singly occupied.
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Arrow Notation• We have learned the long method of
writing out electron configuration.• We can also write electron config.
using the orbital diagram or arrow method.
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For example, the three electrons that are filled into the three 'p'
orbitals can be represented in two different ways:
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• Valence Electrons – outer-shell electrons – Include s and p electrons in the highest energy level– Electrons that are involved in chemical bonding
• Core Electrons = inner-shell electrons• For example, a phosphorus atom has 15 total electrons
– Phosphorus has 5 valence electrons (the electrons in the 3s and 3 p orbitals)
– Phosphorus has 10 core electrons (found in the first and second energy levels)
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• The octet rule atoms tend to form chemical bonds to reach a full outer-shell of 8 valence electrons.
• For example, the phosphorus atom on the previous slide would gain three electrons to reach a full outer shell. This P3- ion would have the same electron configuration as the element argon.
• When an atom and an ion have the same electron configuration, they are said to be isoelectronic.
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• Transition metal ions– d and f electrons are not considered valence
electrons.– Outer shell s and p electrons will be lost first.
• For example:
Fe
Fe2+
Fe3+
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Nobel Gas Notation (Short-Hand)