Chemistry Notes: Chapter 4: sections 4-2 and 4-3: Properties of Light
What happens when white light passes through a prism?
The white light is ___________________________________ into its component wavelengths – it contains light
of all _______________________________ and thus a
__________________________________________________ is produced.
Not all radiation sources produce a continuous spectrum.
When different _______________________ are placed under low pressure in a tube, and high voltage is
applied, the gases emit different ________________________________ of light.
When the light from such a tube is passed through a __________________________, the resulting spectrum
only contains a few ____________________________________ of light.
The colored lines are separated by _______________________________.
Each element has its own _______________________________ spectrum
A spectrum containing radiation of only specific wavelengths is called a
______________________________________________________
Scientists first detected the line spectrum of hydrogen in the mid-1800’s, but couldn’t explain it.
The ______________________________energy state of an atom is called its
__________________________________________________________.
A state in which an atom has a __________________________________________________ than it has in its
ground state is an ___________________________________________.
When current is passed through a gas at low pressure, the potential energy of some of the gas atoms
_______________________________________.
The atoms go from their ____________________________________ to an
___________________________________________________.
When an excited atom returns to its ground state, it ___________________________ the excess energy in the
form of ______________________________________________.
Hydrogen Line Spectrum
Scientists first detected the line spectrum of hydrogen in the mid-1800’s, but couldn’t explain it.
They predicted that the hydrogen atoms could absorb whatever amount of _______________ was added to
them, and thus emit a _______________________________ of light.
When an _______________________ hydrogen atom falls back from an excited state to its
_______________________________ state (or lower energy state) it emits a _______________________ of
radiation
Ephoton=_____________________
The ____________________ of the photon is equal to the difference in energy between the atom’s
___________________________________________
What they saw: hydrogen atoms only emit ____________________________________ of light
What it means: the ______________________________ between the atoms’ energy state are
___________________
The electron of a hydrogen atom exists only in ______________________________________.
In addition to the spectral lines in the ____________________ part of the spectrum, hydrogen also produces
spectral lines in the ________________________ and __________________ regions of the EM spectrum.
Scientists still needed to come up with a model of the hydrogen atom that explained this…
Bohr Model
In 1913 _______________________________ proposed a model of the hydrogen atom that linked hydrogen’s
electron with photon emission.
Bohr Model
The electron can circle the __________________________ only in allowed paths, called
_____________________________.
The electron (and therefore the hydrogen atom) is in its ___________________________ when it is in the orbit
______________________________________to the nucleus.
The electron cannot exist in the _____________________________________ between orbits
The energy of the electron is ______________________________ when it is in orbits that are farther from the
nucleus (__________________________________)
Bohr Model & Spectral Lines
An electron can move to a ____________________________ by gaining an amount of energy
_____________________ to the energy difference between the two orbits.
When the electron falls back to the _____________________________, the excess energy is released as a
_____________________________________________
Draw an example:
From the _________________________________ of the emitted spectral lines, Bohr was able to calculate the
allowed _______________________________ for hydrogen
Bohr’s success in explaining mathematically the spectral lines of hydrogen did not work when trying to explain
the spectra of atoms with more than one electron.
Nor did Bohr’s theory fully explain the _______________________________ behavior of atoms.
Warm-Up – Day 2
Lithium has an atomic weight of 6.941 g/mol. When 10.4115 g of lithium is heated, it emits an energy
measured at 262,500 joules. What is the energy given off by one atom?
4-2 The Quantum Model of the Atom
To explain why energy states of an atom are ____________________, scientists had to change the way they
viewed the nature of the _____________________________.
The ______________________________, and ________________________ showed that light could behave as
both a wave and a particle.
Louis de Broglie – 1924
Suggested that electrons were ____________________ confined to the space around the
__________________________
the waves could only exist at certain _____________________________ that corresponded to specific
__________________________—the quantized energies of Bohr’s orbits
(where E = _____________).
Some more about waves
A beam of electrons passed through a crystal shows the pattern to the right
Why is there a pattern of light and dark rings?
What would you expect to see if you passed light through a tiny slit?
The pattern is due to wave _______________________ and
___________________________.
Wave Interference
Interference is when two waves ____________________________ to form a resultant wave of greater or
lesser magnitude.
Examples:
Wave Diffraction
diffraction involves a change in direction of waves as they pass through an opening or around an obstacle in
their path.
As the waves ______________________ around the obstacle, they experience _____________________
(constructive and destructive)
Further Evidence Shows That The Electron Also Acts As __________________________
Electron beam __________________________ experiments showed the bending of an electron wave as it
passes by the edge of an object, such as an atom in a crystal. The resulting
__________________________________ pattern occurs when waves overlap, resulting in a reduction of
energy in some areas and an increase of energy in others.
Take Home Message…
Diffraction shows that __________________ behaves like a _________________, and
_____________________ also behave like a _________________________.
Why only certain frequencies?
Bohr showed that electron orbits are _________________________ (only exist at certain frequencies).
If we think of the electron wave as being like a wave that is confined to a box of a specific distance, the wave
can only exist stably if it is showing harmonics.
Oh Joy, Another Formula
The wavelength of any orbital can be related to size of the orbit. How?
The value of n gives the first _____________________________, which
indicates the __________________________________ occupied by the
electron.
The Heisenberg Uncertainty Principle (1927)
It is impossible to determine simultaneously both the ______________________ and
___________________________ of an electron or any other particle.
Wave-Particle Duality
Think of the wave-particle duality of matter as this:
A quantum entity, such as a photon or an electron _________________________________, but
_________________________________________.
The Schrödinger Wave Equation (1926)
Together with the uncertainty principle, the wave equation laid the foundation for
___________________________________________________________.
Quantum theory describes mathematically the ___________________________ of
_________________________ and other very small particles.
Solutions to the equations = Wave Functions
The wave functions give only the _____________________________ of finding an electron at a given
place around the nucleus.
Orbitals
The electrons do not travel around the nucleus in neat orbits, as Bohr had thought.
Instead, the electrons exist in certain regions called _________________________________.
An _______________________________ is a three dimensional region around the nucleus that indicates the
probable location of an electron.
Atomic Orbitals and Quantum Numbers
In order to completely describe orbitals, quantum numbers are used.
Quantum numbers specify the _________________________ of atomic orbitals and the properties of electrons
in orbitals.
The first 3 quantum numbers result from solutions to the
____________________________________________________.
Principal Quantum Number ______________
Indicates the ______________________________________ occupied by the electron.
Values of n are positive integers (1, 2, 3…)
As n _______________________, the electron’s energy and average distance from the nucleus
_____________________________.
Angular Momentum Quantum Number ____________
Indicates the __________________________ of the orbital.
For each n the number of orbital shapes possible is equal to n.
The values of l that are allowed are zero and all positive integers less than or equal to n-1.
Angular Momentum Quantum Number (l)
l=0 designates an ______________________________
l=1 designates a ______________________________
l=2 designates a _____________________________
l=3 designates an ______________________________
Magnetic Quantum Number _______________
Indicates the ____________________________ of an orbital around the nucleus.
The values allowed are
m = -l……0…….+l
Spin Quantum Number
Only two possible values, ________________ or _________________
Indicates the two fundamental spin states of an electron in an orbital.
A single orbital can hold a __________________________________________, which must have opposite
spins.
The Quantum Model
Improves upon Bohr’s model because it _______________________________________________________ in
atoms other than hydrogen.
The arrangement of electrons in an atom is known as the atom’s
____________________________________________.
Electrons in atoms tend to assume arrangements that have the lowest possible energies _________________________________________________________________________
Some background info…
To simplify things, we show electrons in orbits around ________________________ (it’s really 3-D orbitals).
There can be a maximum of ________________________________ in the outer shell!!!
But only __________________ gases (Group _____________) are full (ex. Neon)
Rules Governing Electron Configurations
The energy levels of the orbitals are determined and electrons are added to the orbitals one by one according to
3 basic rules:
1. ________________________ principle
2____________________________________________________________________
3____________________________________ rule
Aufbau (“Build-up”) Principle
An electron occupies the
___________________________________________________ that can receive it.
Note: Starting with the third main energy level (n = 3), the energies of the sublevels
begin to _________________________________ (see diagram on p. 105).
Pauli Exclusion Principle (1926)
No _______________________________ in the same atom can have the same set of
____________________________________________________. Thus electron pairs in orbitals must be of
_________________________________ spin.
Hund’s Rule
Orbitals of _____________________ energy are each occupied by _________________________________
before any orbital is occupied by a ______________________ electron, and all electrons in singly occupied
orbitals must have _________________________________________________________
The rule above minimizes ________________________________________________________.
Four Ways of Representing Electron Configurations
1. ______________________________________________________
2. _______________________________________________________________________
3. ______________________________________________________________________
4. By the quantum numbers associated with each electron (you will NOT be held responsible for this on a test).
Terminology that you need to know follows:
1. ________________________________________________________- The electron-containing main energy
level with the _______________________________________________________.
AKA: The outermost shell/orbit
_______________________________ Electrons
Electrons that are _________________ in the highest occupied energy level.
AKA: Everything that is NOT in the outer shell/orbit
Orbital Notation
An unoccupied orbital is represented by a ___________________. The lines are labeled with the
__________________________ quantum number and ___________________________________.
Why 1 line for s-orbitals?
Why 3 lines for p orbitals?
Why 5 lines for d orbitals?
Why 7 lines for f orbitals?
Orbital Notation
1. Draw and label the energy levels of the orbitals (see Fig 4-16 p. 105)
2. Make sure your energy levels are spaced appropriately!
3. Add electrons to the orbitals one by one following the 3 rules.
Orbital Notation - Example
Draw the orbital notation for Boron
Draw the orbital notation for Nitrogen
Draw the orbital notation for Oxygen
Draw the orbital notation for Magnesium
Electron Configuration Notation
Don’t have to draw the lines and arrows 
The number of electrons in a sublevel is shown by adding a ________________________ to the sublevel
designation
Electron Configuration Notation
Write the electron configuration notation for Boron
Write the electron configuration notation for Nitrogen
Write the electron configuration notation for Oxygen
Write the electron configuration notation for Magnesium
Warning!!!!
The electron-configuration notation on your periodic table in the book is NOT in the proper order!!! Do not
copy from the table, use the “yellow brick road”!!!
Example
The electron configuration for an atom is ______________________________________
How many electrons does it have?
What is the atomic number?
What element is it?
In the highest occupied energy level, how many p orbitals are filled?
How many unpaired electrons does this atom have?
Noble Gas Configuration
The outer main energy level is __________________________________, in most cases, by
_______________________ electrons (sometimes called “completing the octet”).
Which noble gas does not complete the octet?
Noble Gas Notation
This is a shorthand method to show _______________________________, usually for atoms in the 3rd period
and beyond. You show the ______________________________ as the core, and then only denote the
__________________________________________ electrons.
Examples:
Weird Variations
Chromium (Cr) expect [Ar]4s23d4, is [Ar]4s13d5
Copper (Cu) expect [Ar]4s23d9, is [Ar]4s13d10
The reason is that mixes of half and/or fully filled orbitals are more stable (in a lower-energy state), than a fully
or half filled orbital with a partially filled orbital.
Which other elements are going to have this same “weird” variation?