1. Chapter 5 Electrons in Atoms
Section 5.3 Electron Configuration
Where is the electron?

2. Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom.
Schrödinger’s equation applied equally well to elements other than hydrogen.
The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.

3. The Quantum Mechanical Model designates energy levels as “principal quantum numbers” (n). The average distance from the nucleus increases with increasing n = 1, 2, 3, 4…
Within each principal energy level, the electrons occupy energy sublevels (as many as the value of n)

4. Probability (Electron cloud)

5. Electron probability clouds are called Atomic Orbitals
Each energy sublevel relates to orbitals of different shape.
one s (spherical) and three p orbitals
all s orbitals are spherical, but as n = 1,2,3 etc. increases, so does its size and energy

6. Each orbital can be occupied by 2 electrons
Four of the five d orbitals have the same shape but different orientations in space.
Each orbital can be occupied by 2 electrons
The maximum number of electrons that can occupy a principal energy level is given by the formula 2n2

7. Which atomic orbitals have a “dumbbell” shape?
A. s
B. f
C. p
D. d

8. Electron Configuration
In most natural phenomena, change proceeds toward the lowest possible energy. High-energy systems are unstable. Unstable systems lose energy to become more stable.
The ways in which electrons are arranged around the nuclei of atoms are called electron configurations
Three rules tell you how to find the electron configurations of atoms.

10. 1. Aufbau Principle Electrons enter orbitals of lowest energy first.
Orbitals within a sublevel (e.g. 2p) are always of equal energy. Within a principal energy level the s sublevel is always the lowest energy sublevel. Yet the range of energy levels within a principal energy level can overlap the energy levels of an adjacent principal level.

13. 2. Pauli Exclusion Principle
An atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins (clockwise and counter-clockwise). A vertical arrow indicates an electron and its direction of spin ( or ).
empty
orbital
orbital,
filled with
2 electrons
orbital, filled
with 1 electron

14. 3. Hund’s Rule
Orbitals of equal energy are being filled with one electron first until all the orbitals contain one electron with parallel spins. (Only subsequent electrons will then completely fill each orbital.)
Three electrons in the 2p energy sublevel
The fourth electron will then pair up in opposite spin

16. 1s2 2s2 2p6 3s2 3p6 4s2 3d8

17. 1s2 2s2 2p6 3s2 3p6 4s2 3d2

20. Orbital diagram (using boxes symbolizing orbitals and arrows up and down as electrons; all in one row)

21. Electron Configuration for Some Selected Elements
Atomic # 1 2 3 6 7 8 9 10 11

22. 3) Noble-gas notation simplifies electron configuration notation by using the chemical symbol in brackets of the last appropriate noble gas which corresponds to the replaced part.
Example silicon: 1s2 2s2 2p6 3S2 3p [Ne] 3S2 3p2
since 1s2 2s2 2p6 is the electron configuration of Neon, Ne

23. The s-, p-, d-, and f-Block Elements
The shape of the periodic table becomes clear if it is divided into blocks representing the atom’s energy sublevel being filled with valence electrons.

26. Without a periodic table a second method can be used, following the diagonal lines. But in our class you will always be allowed to use a periodic table.

27. Exceptions
The Aufbau diagram can be used to write correct ground-state electron configurations for all elements up to and including Vanadium, atomic number 23.
The electron configurations for certain transition metals, like chromium and copper, do not follow the aufbau diagram due to increased stability of half-filled and filled sets of s and d orbitals.

28. Exceptional Electron Configurations
Filled energy sublevels are more stable than partially filled sublevels. Half-filled levels are not as stable as filled levels, but they are more stable than other configurations.
Using the three rules to determine the electron configuration, we would assign chromium and copper the following incorrect configurations
Cr 1s22s22p63s23p63d44s2
Cu 1s22s22p63s23p63d94s2
The correct electron configurations are
Cr 1s22s22p63s23p63d54s1
Cu 1s22s22p63s23p63d104s1

29. Lewis Electron Dot Structures
show valence electrons as dots around the four sides of the element’s symbol.
Your turn:
Cl H Al Ca Xe P .

32. Group 1 metals: alkali metals (Li, Na, K, Rb, Cs) (not, hydrogen)
Group 2 elements alkaline earth metals
Group 17 elements: halogens
Group 18 elements: noble gases = unreactive or inert, because they have the most stable electron configurations with completely filled energy levels or 8 valence electrons (He only 2 valence electrons 1s2, completely filled n=1 level)

33. Which of the following is NOT one of the elemental blocks of the periodic table?
A. s-block
B. d-block
C. g-block
D. f-block

34. Which block spans 14 elemental groups?
A. s-block
B. p-block
C. f-block
D. g-block

35. 2 Review: 1. Who compared atoms with plum pudding? J. J. Thomson
2. Who found the nucleus?
3. Who introduced the Planetary model?
4. In the Quantum mechanical model the
electrons are found in …
5. How many electrons fit in one orbital?
What is the shape of an s-orbital?
What is the shape of a p-orbital?
J. J. Thomson
Rutherford
Bohr
Orbitals 2
Spherical
Dumbbell-shape