Download The Quantum Model of the Atom

THE QUANTUM MODEL OF THE
ATOM
QUANTUM MECHANIC MODEL
• Louis de Broglie
• Werner Heisenberg
• Erwin Schrodinger
ELECTRONS AS WAVES
• Louis de Broglie
• 1924
• Suggested that electrons be considered waves
confined to the space around an atomic nucleus
• Electron waves could only exist at specific
frequencies that correspond to specific energies
THE HEISENBERG UNCERTAINTY
PRINCIPLE
• Werner Heisenberg
• 1927 – German theoretical physicist
• Idea involved the detection of electrons, which are
detected by their interactions with photons
• Because photons have about the same energy as
electrons, any attempt to locate a specific electron
with a photon knocks the electron off its course
•  Results in uncertainty in trying to locate an electron
or any other particle
• Heisenberg uncertainty principle: states that it is
impossible to know both the position and velocity of
an electron or any other particle at a given time
THE SCHRODINGER WAVE EQUATION
• Erwin Schrodinger
• 1926 – Austrian physicist
• Developed an equation that treated electron in
atoms as waves
• Schrodinger equation (+ the Heisenberg uncertainty
principle) laid the foundation for modern quantum
theory
• Quantum theory: describes mathematically the
wave properties of electrons and other small
particles
• Solution to Schrodinger
equation is known as a
wave function
• Only gives the probability
of finding an electron at a
given place around the
nucleus
• Electrons do not travel in
neat orbitals
• Orbital: 3-dimensional
region around the nucleus
that indicated the
probable location of an
electron
ATOMIC ORBITALS AND QUANTUM
NUMBERS
• Quantum numbers: specify the properties of atomic
orbitals and the properties of electrons in orbitals
• Four quantum numbers:
• 1. Principal quantum number
• 2. Angular momentum quantum number
• 3. Magnetic quantum number
• 4. Spin quantum number
• Principal quantum number (n): indicates the main
energy level occupied by an electron
• Only positive integers  n= 1, 2, 3, 4…
• As n increases, the electron’s energy and average
distance from the nucleus increases
• Each main energy level has sub-levels
• Maximum number of electrons in a principal energy
level is n2
• Angular momentum quantum number (l):
indicates the shape of the orbital
• For a specific main energy level, the
number of orbital shapes possible is equal
to n
• Values of l allowed are 0 and all positive
integers less than or equal to n-1
• n=1 has one sublevel (s)
• n=2 has two sublevels (s and p)
• n=3 has three sublevels (s, p, and d)
• n=4 has four sublevels (s, p, d, and f)
Orbital Letter Designations
According to Values of l
Principal
(n)
Angular
momentu
m (l)
Letter
1
0
s
2
1
p
3
2
d
4
3
f
S ORBITAL
P ORBITAL
D ORBITAL
F ORBITALS
• Each atomic orbital is designated by the principal
quantum number followed by the letter of the sublevel
• Examples:
• 1s = the s orbital in the first main energy level
• 1p = the p orbital in the first main energy level
• 2p = the p orbital in the second main energy level
• 4d = the d orbital in the fourth main energy level
• Magnetic quantum number (m): indicates the orientation
of an orbital around the nucleus
• Describes the orientations that correspond to various
values of m  m= -l to +l
• One s orbital in each s sublevel
• Three p orbitals in each p sublevel
• m=-1, m=0, m=+1
• Five d orbitals in each d sublevel
• m=-2, m=-1, m=0, m=+1, m=+2
• Seven f orbitals in each f sublevel
• m=-3,m=-2, m=-1, m=0, m=+1, m=+2, m=+3
• Spin quantum number: indicates the two fundamental
spin states of an electron in an orbital
• Only two possible values: - ½ and + ½
A single orbital can hold a maximum of two
electrons, which must have opposite spins