Transcript Atomic Orbitals and Electron Configurations

Atomic Orbitals & Electron
Configurations
Chemistry
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Atomic Orbitals & Electron Configurations
1. Identify the relationships among a hydrogen atom’s energy
levels, sublevels, and atomic orbitals.
2. Apply the Pauli exclusion principle, the aufbau principle, and
Hund’s rule to write electron configurations using orbital
diagrams and electron configuration notation.
3. Define valence electrons and draw electron-dot structures
representing an atom’s valence electrons.
For the Test:
-be able to answer the objectives
-know all vocabulary
-be able to answer all review/practice questions
-study your notes (anything can be asked from them)
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Atomic Orbitals
Orbitals do not have an exactly defined size, but are just
unoccupied spaces available for electrons should the
atom’s energy increase (or decrease)..
As the energy level increases, the orbital becomes
larger
-n = 1, 2, … 7
The shape of the orbital is represented by the sublevels
in that orbital
-s, p, d, & f
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Atomic Orbitals
Each atomic orbital is designated by energy level and
sublevel:
1s represents ‘s’ orbital in the 1st energy level
each suborbital holds 2 electrons, each with
opposite spin
~s=2
~ p = 6, 3 suborbitals (2 per suborbital)
~ d = 10, 5 suborbitals (2 per suborbital)
~ f = 14, 7 suborbitals (2 per suborbital)
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Electron Configurations
electron configuration: arrangement of electrons in an
atom.
-electrons fill in so they have the lowest possible
energy
-there are three rules we follow
1. Aufbau principle: each electron occupies the lowest
energy orbital available
-follows the aufbau diagram
♦all orbitals in a sublevel are equal energy
♦in multi-electron level, energy sublevels within a
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principle energy level have different energies
♦in order of increasing energy, the sequence of
energy sublevels within a principle energy level is s,
p, d, and f
♦orbitals related to energy sublevels within one
principle level can overlap orbitals related to energy
sublevels within another principle level; begins in
n=3
2. Pauli-exclusion principle: a maximum of 2
electrons may occupy a single orbital, but only if
they have opposite spins
-arrows pointing up (↑)and down (↓) represent
electron spins
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-paired electrons in same orbital: represented by ↑↓.
3. Hund’s rule: single electrons with the same spin
must occupy each equal energy orbital before
additional electrons with opposite spins can occupy
the same orbital
-s sublevel:
p sublevel:
d sublevel:
f sublevel:
max 1 unpaired emax 3 unpaired emax 5 unpaired emax 7 unpaired e-
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Orbital Notation/Electron Configurations
There are three ways to indicate electron configurations.
1. orbital notation: an unoccupied orbital is
represented by a line, ____, with the orbital’s principle
quantum number and sublevel letter written
underneath the line.
___
1s
-an unpaired electron is shown as ____ and
1s
paired electrons as shown as ____ .
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1s
Orbital Notation Practice
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Mg
Al
Si
P
S
Cl
Ar
Cr
As
Kr
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2. electron-configuration notation: eliminates the lines
and arrows of orbital notation
-the number of electrons in a sublevel is shown by
adding a superscript to the sublevel designation;
exs. H configuration is 1s1
(1 electron on the 1s orbital)
He is 1s2
(2 electrons in the 1s orbital)
-use the periodic table to write electron configuration
notation: s, p, d, and f block.
-does not show orbital distributions of electrons
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Electron Configuration Notation Practice
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Mg
Al
Si
P
S
Cl
Ar
Cr
As
Kr
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Noble Gas Notation
3. noble-gas notation: shorthand notation using the
noble gas elements
-noble-gas configuration: outer main energy level
fully occupied by eight electrons, except in He
-ex: Na 1s22s22p63s1 is the electron-configuration
notation (long form)
[Ne]3s1 is the noble gas notation (short form)
because all orbitals are completely filled
up to neon, who’s orbital notation is
1s22s22p6
-this notation is only used for elements above neon!
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(those in n = 3 and above)
Noble Gas Notation Practice
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Mg
Al
Si
P
S
Cl
Ar
Cr
As
Kr
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Exceptions
Some transition metals do not follow this trend.
-includes groups 6 and 11 (Cr and Cu groups)
Cr
[Ar]4s23d4
Cu [Ar]4s23d9
Instead, we write it so that all s and d orbitals after the
noble gas are half filled-increases stablity.
Cr
[Ar]4s13d5
Cu [Ar]4s13d10
Practice with Exceptions:
1. Mo
2. Au
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Valence Electrons
Only certain electrons determine an element’s chemical
properties
-valence electrons: electron’s in the atom’s highest
most energy level
•sulfur has 16 electrons, but only 6 valence electrons
Valence electrons can be determined by writing
electrons configurations:
-S
[Ne]3s23p4
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-Ga
[Ar]4s23d104p1 3
(4th level highest)
[Ar] 3d104s24p1
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Electron Dot Structures
Chemists use valence electrons to show how atom’s are
involved in bonding.
-electron dot structure: consists of the element’s
symbol (which represents the nucleus and inner
electrons) surrounded by dots (that represent the
valence electrons)
•unpair the electrons first along the four sides of the
symbol
S
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Oxidation Numbers
When an atom bonds, it either gains or loses electrons,
forming a charge on the atom
-oxidation number: charge on an atom after bonding
•metals lose to form a positive charge
Ca+2 loses two electrons
•nonmetals gain to form a negative charge
N-3
gains three electrons
Look at the electron dot structure to determine how
many it will lose or gain.
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