Electron Configurations and Sizes

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Transcript Electron Configurations and Sizes

Section 8.4
Ions: Electron Configurations and Sizes
Electron Configurations in Stable
Compounds
• When two nonmetals react to form a covalent bond,
they share electrons in a way that completes the
valence electron configurations of both atoms.
• When a nonmetal and a representative-group metal
react to form a binary ionic compound, the ions form
so that the valence electron configuration of the
nonmetal achieves the electron configuration of the
next noble gas atom. The valence orbitals of the
metal are emptied.
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Section 8.4
Ions
Ions: Electron Configurations and Sizes
An ion is an atom with a charge
Cation – positively charged atom
Anion – negatively charged atom
The question becomes….why do atoms form
ions?
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Section 8.4
Ions
Ions: Electron Configurations and Sizes
Atoms will gain or lose e- in an attempt to form
the same electron configuration as the closest
noble gas.
***Move the LEAST number of e- possible.
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Section 8.4
Ions
Ions: Electron Configurations and Sizes
• Atoms in groups 1 and 2 will lose the outer
valence e- first. These are the “s” e• Atoms in groups 13-15, below the “stairs” will
lose their outer “p” e- first, then their outer
“s” e• Exceptions: B, Al tend to lose both the “p” and
“s” e- at the same time
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Section 8.4
Ions: Electron Configurations and Sizes
Transition Metals – lose their valence “s” e- first,
then they may lose another e- from the “d”
sublevel.
Exceptions: Ag, Zn, Cd – they do NOT lose e- from
the “d” sublevel
Why?
After they lose their “s” electrons, it takes too
much energy to take from the full “d” sublevel
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Rules for Filling Orbitals
– Any orbital may contain 0, 1, or, at most, 2
electrons.
– In filling the p, d, and f subsets, each orbital gets a
single electron with the same spin as the others
before any pairing takes place.
– This is because more energy would be required to
fill them in any other way.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Elements with atomic numbers 14 have only s electrons
Elements with atomic numbers 510 also have electrons in p orbitals
Elements 2130 have d electrons
Elements 5871 have electrons in f orbitals along with all their other electrons.
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Figure 3.18, pg. 78
Investigating Chemistry, 2nd Edition
Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Beryllium has an atomic number of 4, with two 1s electrons and with two
electrons in the 2s orbital. Adding the superscripts gives the total number of
electrons.
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Note the exceptions in red. Copper, Cu, also has an unexpected
configuration.
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Section 8.4
Ions: Electron
Configurations
and Sizes
ELECTRON
CONFIGURATIONS
• It was once suspected that the deposed Emperor
Napoleon was poisoned with arsenic. What is the
electron configuration of arsenic, As, element
number 33?
• Following the periodic table from H, to He, to Li, Be,
B, C, N, O, F, etc.,
– We get 1s2, 2s2, 2p6, 3s2, 3p6…
– So far we have 2 + 2 + 6 + 2 + 6 = 18 e’s.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
• 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p3
• Let’s check our math.
• 18 + 2 + 10 + 3 = 33, the right number of electrons in
a neutral arsenic atom, As.
• Since we followed the periodic table, we did not have
to memorize the fact that the 4s orbital is filled
before the 3d orbitals.
• The set of three 4p orbitals is only half-filled.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
• Because the elements N and P are directly above
arsenic, As, in the periodic table, they also have halffilled p subshells.
• As a result, these three elements have many
chemical similarities.
• Now we can begin to see why Mendeleev was able to
predict the properties of elements and compounds
that had not yet been discovered in 1869.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Electron Orbital Configurations
The configuration may be written by using boxes to
represent each orbital
All orbitals MUST be in increasing energy and MUST
contain a label
1s
2s
2p
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Electron Orbital Configurations
1s
2s
2p
Arrows are used to represent each electron
Before we begin…..
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Three Rules
Aufbau’s Principle – lower energy orbitals fill before proceeding
to higher energy orbitals
Hund’s Rule – When there are multiple orbitals available in a
sublevel, one electron is placed in each orbital before
doubling up the electrons
Pauli’s Exclusion Principle – Within each orbital, e- must spin in
opposite directions; each orbital in a sublevel must spin in the
same direction.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Aufbau’s Principle
To get the orbitals in increasing energy, just
follow the periodic table like you would read a
book.
1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Hund’s Rule
Never double up electrons in an orbital until
each orbital in that sublevel has one electron.
Once each orbital in a sublevel has one electron,
then begin to double up the electrons.
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Pauli’s Exclusions
Principle
Electrons will take the lowest energy configuration
possible. This means:
1. All unpaired e- must spin in the same direction.
2.
All paired e- must spin in opposite directions
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Electron Orbital Configurations
1s
2s
2p
Hydrogen Atomic # =1 , 1e-
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Electron Orbital Configurations
1s
2s
2p
Helium – Atomic Number = 2
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Electron Orbital Configurations
1s
2s
2p
Boron – Atomic Number = 5
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Section 8.4
ELECTRON
Ions:CONFIGURATIONS
Electron Configurations
and Sizes
Stable Compounds
• Atoms in stable compounds usually have a noble gas
electron configuration.
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Noble Gas Configuration
What is a noble gas?
Noble gases are located in group 8A, 18 on
the periodic table.
Noble gases are extremely unreactive,
because their outer energy level is filled
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Noble Gas Configurations
Noble gases include:
He
Ne
Ar
Kr
Xe
Rn
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Noble Gas Configurations
Aufbau tells us that all lower sublevels MUST
be filled before filling sublevels of higher
energy.
This results in us writing the same information
repeatedly when making short hand
configurations:
Mn 1s22s22p63s23p64s23d5
Cl
1s22s22p63s23p5
Ca 1s22s22p63s23p64s2
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Noble Gas Configurations
Rules: Choose the largest noble gas that has
an atomic number LESS than the element
you are working with.
For Mn, the largest noble gas is Ar
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Noble Gas Configurations
Because we know that lower sublevels are
already filled, we can substitute part of the
configuration with a noble gas:
Mn
1s22s22p63s23p64s23d5
Ar
1s22s22p63s23p6
Therefore we write: [Ar] 4s23d5
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Noble Gas Configurations
Now try it for Cl
Cl
1s22s22p63s23p5
The largest noble gas is Ne 1s22s22p6
[Ne] 3s23p5
Valence electrons – these ARE used in
bonding
Core electrons – these are NOT used when
bonding
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Noble Gas Configurations
Write the noble gas configurations for:
As
I
Pb
Au
W
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Noble Gas Configurations
Write the noble gas configurations for:
As
[Ar] 4s23d104p3
I
[Kr] 5s24d105p5
Pb
[Xe] 6s24f145d106p2
Au
[Xe] 6s24f145d9
W
[Xe] 6s24f145d4
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Exceptional
Configurations
….and ions
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Exceptions to Aufbau
There is a general stability associated with
electron configurations



Filled sublevels are MOST stable
½ Filled sublevels are stable
All other configurations for sublevels are
LEAST stable
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Exceptions to Aufbau
Sometimes by moving electrons between
sublevels that are close in energy, atoms can
achieve a more stable configuration.
Examples include:
s 2d 4
Because d5 is ½ filled and more stable, the
atom takes on the configuration of
s 1d 5
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Exceptions to Aufbau
Cr
[Ar] 4s13d5
Mo
[Kr] 5s14d5
W
[Xe] 6s14f145d5
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Exceptions to Aufbau
Another exception occurs with the configuration:
s2d9
Again, by moving 1e- from the “s” sublevel to
the “d” sublevel, the “d” sublevel becomes
filled.
s1d10
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Exceptions to Aufbau
Cu
[Ar]4s13d10
Ag
[Kr]5s14d10
Au
[Xe]6s14f145d10
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WARNING
Exceptional configurations only
happen between “s” and “d”
sublevels….NEVER between “s” and
“p” sublevels.
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