quantum mechanical model (and periodicity) new unit !
DESCRIPTION
u DeBroglie u treated the electron as a function of a wave (Bohr treated as a particle) u Differs from Bohr model in several ways u 2 of particular note u The kinetic energy of an electron is inversely related to the volume of the region to which it is confined (more common – electrostatic energy decreases as kinetic energy increases creating a balance ) u It is impossible to specify the precise position of an electron in an atom at a given instant (the best that can be done is estimate the “probability” of finding an electron in a particular region u Schrodinger u Wave function of electron u Electron cloudTRANSCRIPT
Quantum Mechanical Model(and periodicity)
New unit !
* the distribution of electrons within the orbitals of an
element’s atoms
* determines the chemical properties and reactivity of the elements
DeBroglie treated the electron as a function of a wave (Bohr treated as a particle)
Differs from Bohr model in several ways 2 of particular note
The kinetic energy of an electron is inversely related to the volume of the region to which it is confined (more common – electrostatic energy decreases as kinetic energy increases creating a balance )
It is impossible to specify the precise position of an electron in an atom at a given instant (the best that can be done is estimate the “probability” of finding an electron in a particular region
Schrodinger Wave function of electron Electron cloud
Quantum Mechanical ModelEach electron has it’s own region within the atom and has a number
designation describing that region
1. Principle quantum number (n) ~ main energy level or shell ~ represented by whole number
integers (1, 2, 3 ...the period number on the p-table) ~ number indicates the distance from the nucleus (the > the ‘pqn’ the farther the electrons are from the nucleus)
~ specifies the size of the ORBITAL
Sublevels, sublevels, sublevels2. Azimuthal quantum #~ represented by the letter ‘l ’~ shape of the electron cloud~ the # of sublevels is equal to
the value of the ‘pqn’(‘pqn’ = 2, then there are 2
sublevels)
l = integer from 0 to… (n-1)l = 0, 1, 2, 3…Ex. 1 – 1 = 0 (# representing the “s” sublevel)
Sublevels are?s..p..d..f..g..h..so on
s-sublevel----1 orbital----- ml = 0
p-sublevel ----3 orbitals ----- ml = -1, 0, +1
d-sublevel ----5 orbitals ----- ml = -2, -1, 0, +1, +2
f-sublevel ----7 orbitals ----- ml = -3, -2, -1, 0, +1, +2, +3
ORBITALS
3. Magnetic Quantum number ( ml )
• the quantum number that represents the appropriate orbital
Orbital-orientation quantum #
Within sublevels each electron pair has a different place in space. This space is called an orbital. Max. 2
electrons per orbital
ml = - l to + l
4. Spin Quantum Number (ms)
~ NOT a property of the orbital
~ describes a property of the electron itself
~ indicates the direction of the electron spin ms= +1/2 or -1/2
Electron ConfigurationsElectron Configurations
Orbital notation# = main energy level (pqn, 1, 2, 3 etc…)
letter = sublevel (s, p, d, f)= orbital
= electrons
Here electron, come on boy! Aufbau principle~ electrons are added one
at a time~ you begin with the
lowest energy ~ you add electrons until
all electrons are accounted for
Pauli exclusion principle
~ an orbital can hold a maximum of 2 electrons
~ paired and unpaired
More assigning of electrons Hund’s rule~ all orbitals must have at least one
electron before a paired electron can be used
It doesn’t matter which one gets an electron first, but…
1. Each electron MUST have the SAME SPIN as the others in unfilled orbitals! (up or down)
2. NO electron pairs are allowed until every orbital in that subshell has one electron!
OK…WHY does 4s fill before 3d?
1st shell
Higher energy
“1s” subshell
“2s” subshell“2p” subshell
“3s” subshell“3p” subshell
“3d” subshell
Farther out than 1st shell, but both an equal distance from the nucleus. 2nd shell
3rd shell
Farther out than 2nd shell, but all 3 an equal distance from the nucleus.
Closest to the nucleus
Higher energy
“3s” subshell“3p” subshell
“3d” subshell3rd shellFarther out than 2nd shell, but all 3 an equal distance from the nucleus.
“4s” subshell“4p” subshell
“4d” subshell
4th shellFarther out than 3rd shell, but all 4 an equal distance from the nucleus.
“4f” subshell
Note that, even though the 4th shell is farther out than the 3rd shell, the energy of 4s is LESS than 3d!
1s2s
2p3s
3p3d4s
4p4d
4f5s
5p5d
5f6s
6p6d
6f7s
7p7d
7fHigher energy
•“d” subshells fill 1 shell behind!•3d fills after 4s•4d fills after 5s
•“f” subshells fill 2 shells behind! MORE complex!
•The first “f” subshell is in the 4th shell (4f)…•4f fills after 6s! (then comes 5d, and then 6p)
•5f fills after 7s, (then comes 6d, and then 7p)
Just follow the elements in orderJust follow the elements in order!!!!
““d” and “f ” Subshells Fill LATE d” and “f ” Subshells Fill LATE
Electron “Promotion”Electron “Promotion”A “d” subshell is more stable when it is…EXACTLY 1/2 FULL (5 electrons), or…EXACTLY FULL! (10 electrons)!The same is true for “f ” subshells! (7 or 14 electrons)When a “d” is ONE electron short of 1/2 full or full…It PROMOTES one electron from the nearest “s” subshell!
Electron “Promotion”Electron “Promotion”
Silver (Ag) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s1, 4d10
5s4d
Example: Silver (Ag) 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d9
5s4d
4d9 – 1 short of full!29
110
Silver is now more stable with a full4d subshell! (4d10)
Electron “Promotion”Electron “Promotion”
Remember! One “s” electron will “promote” to the nearest “d” or “f ” subshell if……that “d” or “f ” is one electron short of being full or 1/2 full!Watch for d 4, d 9, f 6 or f 13!
With configuration notation, the concept of orbital notation is still used…BUT The orbitals are no longer represented by boxes
The energy level # and the sublevel are still used (1s, 2s 2p and so on)…BUT The arrows representing the electrons are not used
The number of electrons is still important AND The number of electrons are written as superscripts above the
sublevel designation
Example: Sodium, Na (11 electrons) 1s2 2s2 2p6 3s1
Configuration notationConfiguration notation
Short hand notationShort hand notation With shorthand notation, the same technique as
configuration notation is used. The difference is …
all of the electrons to the previous row NOBLE GAS are accounted for
the configuration continues from the end of the noble gas row and picks up at the beginning of the next energy level
the technique is to put the noble gas element symbol in brackets Ex. [Ar 18]
the configuration notation picks up and continues until all the electrons are accounted for
Ex. Cu29 [Ar18] 4s2 3d9
Practice quantum #’s Consider the following sets of quantum
numbers … a) 3, 1, 0, +1/2 b) 1, 1, 0, -1/2 c) 2, 0, 0, +1/2 d) 4, 3, 2, +1/2
which ones are valid If valid, identify the orbital involved
Atomic Orbital Shapes and Sizes Names derived from the characteristics of their
spectroscopic lines: sharp, principle, diffuse, and fundamental
s p d f and so on…g, h, …
VALENCE ELECTRONSVALENCE ELECTRONS The electrons in the outermost energy level
are called valence electronsvalence electrons. Valence electrons are the ones that cause
chemical properties and reactions Look for the highest “n” (principle energy
level), such as 3s, or 4p, etc. Valence electrons will ALWAYS be in “s” Valence electrons will ALWAYS be in “s”
or “p” subshells!or “p” subshells!
Lewis Dot StructuresLewis Dot StructuresThis is EASY!
The dots placed around the symbol of an element represent ONLY THE OUTSIDE ELECTRONS!These outside electrons are called the…
“valence electrons”!Remember, ONLY “s” AND “p” SUBSHELLS ARE ON
THE OUTSIDE!!!This means that the total number of dots around a
symbol can NEVER exceed 8!! (“s” = 2, “p” =6)This is called the “OCTET RULE”!
Lewis Dot Diagrams
• A Lewis dot diagram illustrates valence electrons as dots around the chemical symbol of an element.
Lewis Dot Diagrams• Each dot represents one valence electron.
• In the dot diagram, the element’s symbol represents the core of the atom—the nucleus plus all the inner electrons.
The dots are written around an imaginary box surrounding the element symbol, up to a maximum of eight!: (no pairs before 5!)
(the dots may start on any side)
Lewis Dot Diagrams Represent Valence Electrons
One outside electron: SyTwo outside electrons: Sy
Three outside electrons: SyFour outside electrons: Sy
Five outside electrons: SySix outside electrons: Sy