Download electron configuration days 1

Unit 4
Electron Configurations
Unit 4 Learning Goals
• To understand why the electron cloud model of the atom is more appropriate than the orbital model of the atom.
• To understand and apply Heisenberg’s Uncertainty Principle, Aufbau
Principle, Pauli Exclusion Principle and Hund’s Rule to electron configurations. • To write the longhand and shorthand electronic configurations for atoms.
• To identify the period number, block and group number for a given atom from its electron configuration.
• To write the orbital diagram for a given atom or ion.
• To identify the number of valence electrons from an atom’s electron configuration.
• To write a Lewis Dot Diagram for a given atom.
• To explain Planck’s Theory and how the existence of quantized energy levels relate to atomic emission spectra.
Match the Term/Concept with Info
Electron cloud
a
Subdivision of energy level; the numeric value of energy level is equal to the total number of these in that energy level
Energy level
b
You cannot know the location and momentum of an electron at the same time
Orbital
c
The area around the nucleus comprised of all the energy levels; probability of location of electrons is greatest near the nucleus
Energy sublevel
d
Hold a maximum of 2 electrons; Heisenberg’s Uncertainty
Principle
e
3 dimensional regions of space around nucleus where electrons are most likely to be found; aka shell
Match the Term/Concept with Info
Electron Configuration
f
Empty Bus Seat Rule; electrons occupy equal‐energy orbitals so that a maximum number of unpaired electrons results
Pauli Exclusion Principle
g
These describe certain aspects of the locations of electrons; n, l,
m, s
Aufbau Principle
h
Only a max of 2 electrons in each orbital and they must have opposite spins
Hund’s Rule
i
This shows the number of electrons in each sublevel in each energy level of ground‐state atom
Quantum Numbers
j
Lazy Tennant Rule; electrons fill lowest energy orbitals first
Bohr Model of Atom
It is a planetary model in which the negatively‐charged electrons orbit a small, positively‐charged nucleus
Main Points of the Bohr Model
• Electrons orbit the nucleus in orbits that have a set size and energy.
• The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
• Radiation is absorbed or emitted when an electron moves from one orbit to another.
Heisenberg’s Uncertainty Principle • Every particle has a wave associated with it; each particle actually exhibits wavelike behavior. • The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. • Applicability to Electrons:
– you can measure the location of an electron, but not its momentum (energy) at the same time.
http://www.physicsoftheuniverse.com/scientists_planck.html
Clouds and Quantum Numbers
• Instead of traveling in defined orbits or hard, spherical “shells,” as Bohr proposed, electrons travel in diffuse clouds around the nucleus.
• To describe the location of electrons, we use quantum numbers. Quantum numbers are basically used to describe certain aspects of the locations of electrons.
Quantum Mechanical (aka Electron Cloud) Model of Atom
Electron energy levels are not
neat, planet‐like orbits
They are 3‐
dimensional spherical regions of space (clouds) around the nucleus in which electrons are most likely to be found.
Electron Clouds
• The electron cloud is darkest at the nucleus and gradually gets lighter as you travel away. • This color gradient is based on electron probability, the likelihood of finding an electron in a certain location. The chances of finding an electron decrease as you get farther away from the nucleus. • The properties of an atom's electron configuration are described by four quantum numbers
http://education-portal.com/academy/lesson/electron-cloud-definition-model-theory.html#lesson
Quantum Numbers
1. The principal quantum number (n) describes the size of the orbital and indirectly describes the energy of an orbital. (Energy Level 1‐7)
2. The angular quantum number (l) describes the shape of the orbital. (s, p, d, f)
3. The magnetic quantum number (m), describes the orientation in space of a particular orbital. (# of orbitals = # of options)
4. The spin quantum number (s) distinguishes between the two electrons in an orbital. The s-sublevel
(1 orbital)
The p-sublevel
(3 orbitals)
The d-sublevel
(5 orbitals)
The f-sublevel
(7 orbitals)
Electron Configurations
• The principal quantum number (n) = the Energy level (sometimes called the shell)
– n= 1‐7
• Each energy level has sublevels associated with it
– The number of sublevels within a level is equal to n.
– They are called s, p, d, f, etc. (n=1 has s; n=2 has s & p; n=3 has s, p, & d; n=4 has s, p, d, & f, etc.) • Each sublevel has one or more orbitals within it
– s has 1, p has 3, d has 5, f has 7
• Each orbital can hold no more than 2 electrons
– “spin up” and “spin down”
Electron SubLevels
Principle Quantum Number
1
2
3
4
5
6
7
Number of Sublevels
Labels for Sublevels
1
2
3
4
5
6
7
s
s,p
s,p,d
s,p,d,f
s,p,d,f,g
s,p,d,f,g,h
s,p,d,f,g,h,i
Due to maximum atomic number, no sublevel g, h, or i exists.
Apartment Building Analogy
• Energy levels are like floors in an apartment building – Higher energy level means bigger floor and more sublevels
• Each energy level is divided into sublevels which are like the apartments on the floor
– Higher energy levels are larger, so they have more
sublevels or apartments
• Each sublevel contains orbitals which are like the bedrooms in an apartment – Bigger sublevels or apartments have more bedrooms
• Each orbital can contain no more than 2 electrons or roommates in a room
Connecting l quantum number to number of sublevels • To identify what type of possible sublevels n
has, these sublevels have been assigned letter names. The value of l determines the name of the subshell
Name of Sublevel
Value of l
s sublevel
0
p sublevel
1
d sublevel
2
f sublevel
3
Connecting quantum numbers with total number of orbitals
s orbitals
p orbitals
d orbitals
f orbitals
l
0
1
2
3
m
0
‐1, 0, +1
Number of orbitals in designated sublevel
1
3
‐2, ‐1, 0, +1, ‐3, ‐2, ‐1, 0, +2
+1, +2, +3
5
7
http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/10%3A_Multi‐
electron_Atoms/Quantum_Numbers#A_Closer_Look_at_Shells.2C_Subshells.2C_and_Orbitals
Electron Orbitals and Sublevels
Each orbital holds 2 electrons
Electron Sublevels and Orbitals
(2 Electrons per Orbital)
Sublevel
# of Orbitals # of Electrons
s
1
2
p
3
6
d
5
10
f
7
14
Expanding the Analogy
• Imagine electrons are moving into an apartment complex:
Electrons don’t like to waste energy climbing to apartments on higher floors. Electrons don’t like to waste energy caring for larger apartments. Electrons move into the most energy efficient apartments first.
Electron Configurations
• The electron configuration of an atom shows the number of electrons in each sublevel in each energy level of the ground‐state atom.
• The basis of this prediction is a rule known as the aufbau principle, which assumes that electrons are added to an atom, one at a time, starting with the lowest energy orbital, until all of the electrons have been placed in an appropriate orbital.
Aufbau Principle
–Electrons fill the lowest energy orbitals first.
–This creates stable atoms
–“Lazy Tenant Rule”
Pauli Exclusion Principle
 Each suborbital can hold at most TWO electrons and these electrons must have opposite spins.
Hund’s Rule
 Electrons occupy equal‐energy orbitals so that a maximum number of unpaired electrons results.
 “Empty Bus Seat Rule”
 To draw, fill each orbital with an “up” arrow first, then fill in the “down” arrow
WRONG
RIGHT
Example
O
16
8
Orbital (Aufbau) Diagram
1s
2s
Electron Configuration
2
2
4
1s 2s 2p
2p
Aufbau Diagram, Electron Configuration, Lewis Dot Structure
1s
2s
2p
3s
3p
4s
3d
Electron configuration _____________________________ Dot structure
1s
2s
2p
3s
3p
4s
3d
Electron configuration _____________________________ Dot structure
1s
2s
2p
3s
3p
4s
3d
Electron configuration _____________________________ Dot structure
1s
2s
2p
3s
3p
4s
3d
Electron configuration _____________________________ Dot structure
Blocks in the Periodic Table
Each “suborbital” holds 2 electrons spinning
in opposite directions
Filling Sequence with Rules
How and Where are Electrons “Stored”
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f 5g
6s 6p 6d 6f 6g 6h
7s 7p 7d 7f 7g 7h 7i
• Electrons fill in the order that creates the most stability (Aufbau Principle)
• Use a diagonal pattern to establish filling sequence.
• When comparing the sequence to the “blocked out” periodic table, you will notice not all sublevels are in use
How and Where are Electrons “Stored”
•
Electrons fill in the order that creates the most stability (Aufbau Principle)
•
You sometimes fill sublevels in the 4th
energy level before all of the sublevels in the 3rd energy level are filled.
•
Use a diagonal pattern to establish filling sequence.