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Section 5.3 Electron Configurations

Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

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Page 1: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Section 5.3

Electron Configurations

Page 2: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

ObjectivesApply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations using orbital diagrams and electron configuration notation.Define valence electrons and draw electron-dot structures representing an atom’s valence electrons.

Page 3: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron ConfigurationsEnergy and stability play an important role in determining how electrons are arranged in atoms.In the atom, electrons and the nucleus interact to make the most stable arrangement possible.Electrons are “arranged” so that the atom is in its lowest possible energy state.

Page 4: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron ConfigurationsThe ways in which electrons are arranged into various orbitals around the nuclei of atoms are called electron configurations.3 rules or principles define how electrons can be arranged in an atom’s orbitals.

Page 5: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations

1. The Aufbau Principle states that electrons occupy the orbitals of lowest possible energy.

This diagram is called an orbital or Aufbau

diagram.Each box represents

an atomic orbital.

Page 6: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

The Aufbau Principle Since orbitals for any sublevel of a

principal energy level have an equal energy status (all 3 p orbitals have equal energy, for example) AND since within an energy level the energy increases from the s to the p’s to the d’s to the f’s, filling the atomic orbitals with electrons proceeds from the bottom to the top in the Aufbau diagram.

Page 7: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

The Aufbau PrincipleNotice in Fig. 18 (pg. 156) in your text, energy levels begin to overlap at about n=4.We cannot, therefore, follow a simple pattern when placing electrons in orbitals. We need to follow an Aufbau diagram!

Page 8: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations2. The Pauli

Exclusion Principle states that a maximum of 2 electrons may occupy a single atomic orbital. To occupy the same orbital, the electrons must have opposite spin. A vertical arrow indicates an

electron and its direction of spin.

Page 9: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations3. Hund’s rule

states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital.

Carbon has 6 electrons:the first 2 go into the 1s orbital; the next 2 go intothe 2s orbital; the last 2 go into separate 2p orbitals.

Page 10: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Practice Problems

Use an Aufbau diagram to determine electron placement for:

1. nitrogen 2. oxygen 3. fluorine 4. neon

Page 11: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations

Page 12: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron ConfigurationsA shorthand method for indicating an electron configuration involves1. writing the energy level and the symbol for

every sublevel occupied by an electron; 2. then, indicating the number of electrons

occupying that sublevel with a superscript.

Examples: Hydrogen: 1s1

Oxygen: 1s2 2s2 2p4

(Note: the sum of the superscripts equals the number of electrons in the atom.)

Page 13: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations• An even shorter

method for writing electron configuration involves noble gases.

• Noble gas notation uses noble gas symbols in brackets to shorten inner electron configurations of other elements.

Page 14: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron Configurations Write the electron configurations and

noble-gas configurations for each atom.

1. hydrogen 2. lithium 3. boron 4. nitrogen 5. fluorine

Page 15: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

ExceptionsChromium and copper are 2 examples of exceptions to the Aufbau Principle.These exceptions are due to subtle electron-electron interactions in orbitals with similar energies.

Cr 1s2 2s2 2p6 3s2 3p6 4s1 3d5 Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10

Page 16: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Valence ElectronsValence electrons are defined as electrons in the atom’s outermost orbitals. These are the electrons in the atom’s highest principal energy level.Valence electrons DETERMINE THE PROPERTIES of an element.They are easy to identify in electron configuration :

S 1s2 2s2 2p6 3s2 3p4 There are 6 valence electrons, identified as 3s2 3p4

Page 17: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron-dot (or Lewis) Structures

Since valence electrons are involved in bond formation, scientist use a visual shorthand to represent them. The element’s symbol is written. It represents

the nucleus and all inner-level electrons of the atom.

Dots are drawn to represent the valence electrons.

Proper placement of dots is important. They are placed 1 at a time on the 4 “sides” of the symbol and then they are paired up until all are used.

Page 18: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Electron-dot (or Lewis) Structures

Page 19: Section 5.3 Electron Configurations. Objectives Apply the Pauli exclusion principle, the Aufbau principle, and Hund’s rule to write electron configurations

Practice Problems Draw the electron-dot structures

for the following: 1. Phosphorus 2. Argon 3. Nickel 4. Bromine