Download Unit 3 – Quantum Mechanical Model of the Atom

Chapter 4:
Quantum Mechanical
Model of the Atom
Radiant Energy
• Waves: energy travels through
space by electromagnetic
radiation
• All electromagnetic radiation
travel at the “speed of light”
• c=3.0 x 108 m/s
Visible Light
Parts of a Wave
Wave Terms
• Wavelength: distance between 2 waves
– Symbol: λ, measured in meters, centimeters, etc.
• Frequency: how often a wave crest passes a
given point in one second.
– Symbol: υ, measured in seconds-1 (s-1)or Hertz (Hz)
• Wavelength & Frequency are inversely
proportional
– Speed of a wave = wavelength x frequency
Practice Problem
KDWB broadcasts on a frequency of 101.3
MHz (101.3 FM = 101,300,000 s-1). What
is the wavelength?
Energy “Quantized”
• Energy is absorbed by objects in quantized or
fixed amounts.
• Photoelectric effect: Electrons are ejected
from the surface of a metal when light shines
on its surface.
• Each metal requires a minimum frequency of
energy to release electrons.
• Light consists of quanta of energy that behaves
like tiny particles, or photons.
Atomic Line Spectra
• Spectrum that contains only certain
colors.
• Giving elements energy causes the
electrons to jump up energy levels, fall
back and emit light.
• The light corresponds to a certain
wavelength & certain color.
Bohr Model of the Hydrogen Atom
• If elements give off unique line spectra, then
the energy of the electron must be quantized.
• Each energy level was given a specific value;
1, 2, etc.
• When an electron absorbs a specific amount of
energy, it jumps from its ground state to an
excited state.
• When the electron falls back to the ground
state, energy is given off in the form of light.
• Bohr used Planck’s equation, E = hv, to verify
this theory for hydrogen.
Wave-Particle Duality
• Louis DeBroglie verified that matter
can have wave properties and waves
can have matter properties.
• We don’t see the wave behavior of a
particle unless the particle is
extremely small (like an atom).
Heisenberg’s Uncertainty Principle
• It is impossible to know both the position
& the momentum of an object (particle)
at the same time.
• Treating an electron like a wave helps us
trace it’s movement in a more predictable
pattern.
• Schrodinger came up with a complicated
wave equation to determine the location
of the electrons in an atom.
Quantum Numbers
• Each electron in an atom is described
by 4 quantum numbers.
• Pauli Exclusion Principle: no 2
electrons in an atom can have the
same set of 4 quantum numbers.
Quantum-Mechanical Model
• Electrons live in “orbitals”.
• An orbital can hold up to 2 electrons.
• Orbitals are found in sublevels in an
energy level.
• An orbital describes where we can find
an electron 90% of the time.
Energy Levels & Sublevels
Main Energy Levels & Accompanying Sublevels:
n = 1 has an s sublevel
(1 sublevel)
n = 2 has s & p sublevels
(2 sublevels)
n = 3 has s, p & d sublevels
(3 sublevels)
n = 4 has s, p, d & f sublevels
(4 sublevels)
Maximum electrons in each sublevel:
s holds up to 2 electrons
p holds up to 6 electrons
d holds up to 10 electrons
f holds up to 14 electrons
1 orbital
3 orbitals
5 orbitals
7 orbitals
4f
n=4
4d
4p
3d
4s
n=3
3p
3s
2p
n=2
2s
n =1
1s
Energy
Nucleus
Summary: Principle Levels & Sublevels for a Neutral
Zn atom (30 electrons).
f
d
n=4
Energy
p
d
s
p
n=3
s
p
s
s
n=2
n=1
1s2 2s2 2p6 3s2 3p6 4s2 3d10
- When adding electrons to an atom or ion, then start at lowest principle level & lowest
sublevel and work on up to highest energy.
- Two Problems:
1) Need simple writing method: Number = Principle Level & Letter = Sublevel
2) n= 3, 4, 5, 6 & 7 levels have overlaps.
Following diagram predicts order of filling.
1s
2s
2p
3s
3p
3d
4s
4p
4d
4f
5s
5p
5d
5f
6s
6p
6d
6f
7s
7p
7d
7f
Electron Configurations - Practice
Write the electron configuration of each of the
following elements:
a. Na
b. Zn
c. Te
d. Pt
III. Electronic Energy Levels
1A s1
1e
2A s2
2e
3A s2p1
3e
4A s2p2
4e
5A s2p3
5e
Transition Metals – filling d
subshell
Inner Transition
Metals – filling f
subshell
6A s2p4
6e
7A s2p5
7e
8A s2p6
8e