Unit 6: Chapters 11-12. Pages 295-366 ATOMIC ELECTRON CONFIGURATIONS AND PERIODICITY. Bohr Model. First model of the electron behavior Vital to understanding the atom Does not work for atoms with more than 1 electron. Collision of Ideas. Matter. Dalton. Thompson. Rutherford. Bohr. ?.
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more than 1 electron
Duality of Light
Light was “known” (thought) to be a wave, but
Einstein showed that it also acts particle-like
Electrons were particles with known mass & charge
What if ……
electrons behaved as waves also
Diffraction pattern obtained with firing a beam of electrons through a crystal.
This can only be explained if the electron behaves as a wave!
Nobel Prize for de Broglie in 1929
A baseball behaves as a particle and follows a predictable path.
An electron behaves as a wave, and its path cannot be predicted.
All we can do is to calculate the probability of the electron following a specific path.
All we can predict is…..
The Uncertainty Principle
Wave Equation & Wave Mechanics
Gives the most probable location of electron in 3-D space around nucleus (probability map)
- most probable
location called an
- orbitals can hold a
maximum of 2 e-
Electron’s energy is quantized
Mathematics of waves to define orbitals
Suppose the size of the probability distribution is defined
as where there is a % chance of all hits being confined.
The electron's movement cannot be known precisely.
We can only map the probability of finding the electron at various locations outside the nucleus.
The probability map is called an orbital.
The orbital is calculated to confine 90% of electron’s range.
Electrons in atoms are arranged as
SHELLS (n) = distance from nucleus
1, 2, 3, …
SUBSHELLS (l) = shape of region of probability
s, p, d, f
ORBITALS (ml) = orientation in space
Principal quantum number (n) = number of subshells
The 2s orbital is similar to the 1s orbital, but larger in size.
”Larger” means that the highest probability for finding the electron lies farther out from the nucleus.
Each can hold a maximum of
The 2p orbital is in the n = energy level.
There are 2p orbitals oriented in three directions.
Each orbital can hold a maximum of electrons.
The maximum number of electrons in the 2p sublevel is .
Adding all 2p orbitals would result in a sphere.
The five 3d orbitals are generally oriented in different directions.
Adding all five orbitals, would result in a sphere.
The five orbitals, taken together, make up the d subshell of the n = 3 shell.
Each orbital can hold a maximum of two electrons.
This sublevel has a maximum of electrons.
Each orbital can be assigned no more than 2 electrons! And each electron spins in opposite directions.
Diamagnetic: NOT attracted to a magnetic field
Paramagnetic: substance is attracted to a magnetic field. Substance has unpaired electrons.
n ---> shell1, 2, 3, 4, ...
l ---> sublevels, p, d, f
ml ---> orbital -l ... 0 ... +l
ms ---> electron spin+1/2 and -1/2
Determine the quantum numbers for the outer two valence electrons in the lithium atom.
for H, atomic number = 1
value of l
value of n
Two ways of writing configs. One is called thespdf notation.
Broad Periodic Table Classifications
Two ways of writing configs. Other is called theorbital box notation.
One electron has n = 1, l = 0, ml = 0, ms = + 1/2
Other electron has n = 1, l = 0, ml = 0, ms = - 1/2
Energy ordering of orbitals for multi-electron atoms
Different subshells within the same principal shell have different energies.
The more complex the subshell, the higher its energy. This explains why the 3d subshell is higher in energy than the 4s subshell.
Rules for Filling Orbitals
Bottom-up (Aufbau’s principle)
Fill orbitals singly before doubling up (Hund’s Rule)
Paired electrons have opposite spin (Pauli exclusion principle)
Hund’s Rule- electrons in the same sublevel will spread out into their own orbital before doubling up.
Valence Electrons by Group
All the elements in a group have the same electron configuration in their outermost shells
Example: Group 2
Mg 2, 8, 2
Ca 2, 2, 8, 2
Specify if each pair has chemical properties that are similar (1) or not similar (2):
A. Cl and Br
B. P and S
C. O and S
Higher effective nuclear charge
Electrons held more tightly
Electrons held less
1. Atomic and ionic size2. Electron affinity
3. Ionization energy 4. Metallic Character
Electron cloud for 1s electrons
Increase in Z* across a period
Does the size go
up or down when losing an electron to form a cation?
, 78 pm
2e and 3 p
Forming a cation.
3e and 3p
Does the size go up or down when gaining an electron to form an anion?
F, 71 pm
, 133 pm
9e and 9p
10 e and 9 p
Forming an anion.
IE = energy required to remove an electron from an atom in the gas phase.
Mg (g) + 738 kJ ---> Mg+ (g) + e-
Mg (g) + 735 kJ ---> Mg+ (g) + e-
Mg+ (g) + 1451 kJ ---> Mg2+ (g) + e-
Mg2+ (g) + 7733 kJ ---> Mg3+ (g) + e-
Energy cost is very high to dip into a shell of lower n. This is why ox. no. = Group no.
A few elements GAIN electrons to form anions.
Electron affinity is the energy involved when an atom gains an electron to form an anion.
A(g) + e- ---> A-(g)
E.A. = ∆E
∆E is EXOthermic because O has an affinity for an e-.
EA = - 141 kJ
The text links metallic character to the tendency to lose electrons in chemical reactions, and nonmetallic character to the tendency to gain electrons in chemical reactions. The metallic character trends therefore follow the ionization energy trends