as we saw earlier, the bohr model had several short comings the model currently used to describe...
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As we saw earlier, the Bohr Model had several short comings
The model currently used to describe the atom is the Quantum Mechanical Model of the atom
This is the current theoretical framework that is used to describe all of the information we have about atoms and how they function
Quantum (plural ‘quanta’)A finite amount of energy
i.e. – an energy level in an atomThe amount of energy required to move
an electron from its present energy level to the next higher one
MechanicalMovement of parts in relation to a whole
i.e. – electrons in an atom Hence the Quantum Mechanical
Model deals with the movement and location of electrons in an atom
The double-slit experiment showed that electrons could be anywhere, they are not confined to one path
We cannot know where an electron is and where it is going
Because of this, we use probability to determine where an electron is most likely to be
Using the electron probabilities, we find areas where electrons are most likely to be
These areas are called electron clouds where the probabilities of finding electrons is very high
The shapes and distance from the nucleus of these electron clouds depends on several factors
To describe electron clouds and where electrons probably are, we use quantum numbers
There are a total of four (4) quantum numbers as illustrated in the chart:Principal Quantum NumberAngular Quantum NumberMagnetic Quantum NumberSpin Quantum Number
Principal Quantum Number
n
n can equal 1-7
Refers to the energy level or distance from the nucleus; Represented by the letter n. n is a number from 1-7 to describe the period on the periodic table the element is in
Angular Quantum Number
L
L can equal
0 to (n-1)
The shape of the orbital; represented the letters s, p, d, and f. Each letter also has a corresponding number
s=0, p=1, d=2, f=3
Magnetic Quantum Number
mL
ml = -L to +L
Determines the orientation of the orbital in space in reference to other orbitals
Spin Quantum Number
ms
ms = +1/2 and -1/2
Specifies the value for spin; electrons in the same orbital must spin in opposite directions
Principal Quantum NumberEnergy levelDistance away from the nucleus
As # increases, distance from the nucleus also increases
As the number increases, so does the energy of the electrons in those orbitals
Represented by integers 1,2,3,4,5,6,7 that correspond to the seven horizontal rows on the periodic table Determined by counting as you move down (top
to bottom) the periodic table
Angular Quantum Number Also known as “sub-shells” Refer to the shape of the orbital There are four (4) different shapes
S, P, D, F These correspond to the s, p, d, f blocks on the periodic table
“S” Sub-shell Spherical shape N=0
Only one (1) orbital per energy level
This is because the Magnetic Number, mL is from –L to +L
The 1 sub shell can hold 2 electrons One with +1/2 spin One with -1/2 spin
“P” Sub-shell Dumbbell shape n=1 Three (3) orbitals per
energy level mL and be from –L to +L
Each shell can hold 2 electrons 3 orbitals mean the p-
shell can hold up to 6 electrons
“D” Sub-shellTend to have a
clover-leaf shapen=2Five (5) orbitals per
energy levelEach can hold a
maximum of two (2) electrons Can hold a max of 10
electrons
“F” Sub-shellShape contains 6
lobes for the most part
Seven (7) orbitals per energy level
Each can hold a maximum of two (2) electrons
Fourteen (14) electrons total at each energy level
Sub-shellSub-shell Energy Energy level (n) in level (n) in which it is which it is first foundfirst found
Number of Number of sub-shells sub-shells at a levelat a level
Number of Number of electrons in electrons in these sub-these sub-shellsshells
SS 11 11 22
PP 22 33 66
DD 33 55 1010
FF 44 77 1414
Spin Quantum NumberRemember, in each
sub-shell there can be two (2) electrons
These electrons must have spins that go in opposite directions
Represented by arrows pointing in opposite directions
1. Which of the following describes the 4p orbital?
a. n=1, L=0b. n=4, L=1c. n=2, L=-1d. n=3, L=0
2. Which of the following is not a possible set of quantum numbers?
a. n=1, L=2, mL=-2
b. n=1, L=1, mL=-1
c. n=1, L=0, mL=1
d. n=1, L=0, mL= 0
There are two (2) different types of notation used to represent the quantum mechanical model:Orbital NotationElectron Configuration Notation
Illustrates the following quantum numbers: principal, second (shape), and spin
Use the template to draw and “fill” the sub-shells with electrons
Order of filling electrons is governed by three (3) rules:Aufbau PrinciplePauli Exclusion PrincipleHund’s Rule
Aufbau Principle:Electrons enter sub-shells of lowest
energy first1st energy level fills up before the next
Pauli Exclusion Principle:All atomic sub-shells contain a maximum
of two (2) electrons. Each MUST have a different spin
Hund’s Rule:when electrons occupy sub-shells of equal
energy, ONE electron enters EACH sub-shell until all the sub-shells contain one electron with identical directions
Electrons are added to sub-shells so that a maximum number of unpaired electrons result