Chapter 5. Electron Configurations and Periodic Trends. True Nature of Waves and Particles. Bohr’s model has some flaws. Bohr’s model has set tracks for electrons to travel, but in reality they were in all space almost at the same time. Like a ceiling fan rotating in three dimensions.
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Electron Configurations and Periodic Trends
Bohr’s model has some flaws.
Bohr’s model has set tracks for electrons to travel, but in reality they were in all space almost at the same time. Like a ceiling fan rotating in three dimensions.
Heisenberg uncertainty principle – it is impossible to know both the exact position and the exact momentum of an object at the same time.
 the more that we know of one, the less we know of the other.
 treats electrons as particles
 tried to treat electrons as waves.
 came up with an elaborate equation to describe the location of an electron based upon certain quantum numbers
 Measured in meters
Highest Frequency Lowest Frequency
Higher Energy Lower Energy
MICROWAVES
Communication
Electromagnetic Spectrum
5
(m/s) (m) (Hz)
Ex. 1 What is the frequency of yellow light which has a wavelength of 580 nm?
Ex. 2 What is the wavelength of the signal from 1100AM which has a frequency of 1100 Megahertz?
We can actually see electrons moving down in energy level through flame tests…energy given off corresponds to the color of the flame produced…
Schrodinger proposed four different quantum numbers to describe the location of an electron around a nucleus.
Principle quantum number (n) through flame tests…energy given off corresponds to the color of the flame produced…– corresponds to energy level
 goes in order of 1,2,3,…with one being the lowest in energy
 n is also used to tell us the distance that an electron is from the nucleus.
 based on the period (or row) in periodic table
Greatest number of electrons per energy level is given by the equation 2n2.
(ex: How many e in the 1st energy level?
 the 2nd?
 the 3rd?
 Sublevels  smaller energy states grouped inside a larger energy level
s < p < d < f
Mnemonic tool: “some people don’t fart” or make up your own
Number of types of principal quantum energy level?
orbitals in energy level = number
Energy LevelSublevels
1st energy level 1s
2nd energy level 2s 2p
3rd energy level 3s 3p 3d
4th energy level 4s 4p 4d 4f
An orbital is the region that you are most likely going to find a specific electron.
Shapes of orbitals:
s – spherical p – barbell shaped (each centered on a different axis – x,y,z)

Orbital energy level? – region occupied by one pair(2) of electrons.
 s has one orbital = 1pair (2 electrons)
 p has three orbitals = 3 pairs (6)
 d has five orbitals = 5 pairs (10)
 f has seven orbitals = 7 pairs (14)
Overlapping occurs in the third and fourth energy level, as it takes more energy to put an electron into a “d” than an “s” or a “p”…
 “d” is filled one energy level later.
 “f” is filled two levels later.
These shapes are filled later because they are so complex and require additional energy to enter.
 electrons will singly fill each orbital until all orbitals have one atom before putting two electrons in one orbital.
 example: filling rooms in a hotel, seats on an airplane
– describes difference between two electrons occupying the same orbital.
with differing spins:
We can use arrows or number and letter configurations to represent the electron configurations.
 for arrows, all arrows should add up to the total number of electrons (atomic number)
 for plain configurations, superscripts should add up to the total number of electrons
Ex: H, He, O, Ca, Cd, let’s do both arrow and plain config.
Electron dot diagram – shows only electrons in the outermost energy levels  only looks at the “s” and the “p”
 diagrams should represent filled orbitals
Ex: H, He, O, Ca, Cd
Summation: How do we treat electrons: as a particle, wave, or a cloud of charge?
Whichever way works best. Electrons prescribe to all three.