1. Section 3: Electron Configuration
Three rules are used to determine electron arrangement in an atom. K
What I Know W
What I Want to Find Out L
What I Learned

2. 6(E) Express the arrangement of electrons in atoms through electron configurations and Lewis valence electron dot structures.
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Electron Configuration

3. Essential Questions
How are the Pauli exclusion principle, the aufbau principle, and Hund’s rule used to write electron configurations?
How do electron-dot structures represent an atom’s valence electrons?
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Electron Configuration

4. Vocabulary Review New electron electron configuration aufbau principle
Pauli exclusion principle
Hund’s rule
valence electron
electron-dot structure
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Electron Configuration

5. Ground-State Electron Configuration
The arrangement of electrons in the atom is called the electron configuration. The aufbau principle states that each electron occupies the lowest energy orbital available.
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Electron Configuration

6. Ground-State Electron Configuration
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Electron Configuration

7. Ground-State Electron Configuration
The Pauli exclusion principle states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins.
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 energy level orbitals.
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Electron Configuration

8. Ground-State Electron Configuration
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.
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Electron Configuration

9. Valence Electrons
Valence electrons are defined as electrons in the atom’s outermost orbitals—those associated with the atom’s highest principal energy level. Electron-dot structure consists of the element’s symbol representing the nucleus, surrounded by dots representing the element’s valence electrons.
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Electron Configuration

10. Electron-Dot Structures
SOLVE FOR THE UNKNOWN
Tin has an atomic number of 50. Thus, a tin atom has 50 electrons.
Write out tin’s electron configuration using noble-gas notation. The closest noble gas is Kr.
[Kr]5s24d105p2
The two 5s and the two 5p electrons (the electrons in the orbitals related to the
atom’s highest principal energy level) represent tin’s four valence electrons. Draw the four valence electrons around tin’s chemical symbol (Sn) to show tin’s electron-dot structure.
Use with Example Problem 3.
Problem
Some toothpastes contain stannous fluoride, a compound of tin and fluorine. What is tin’s electron-dot structure?
Response
ANALYZE THE PROBLEM
Consult the periodic table to determine the total number of electrons in a tin atom. Write out tin’s electron configuration, and determine its number of valence electrons. Then use the rules for electron-dot structures to draw the electron-dot structure for tin.
EVALUATE THE ANSWER
The correct symbol for tin (Sn) has been used, and the rules for drawing electron-dot structures have been correctly applied.
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Electron Configuration

11. Review Essential Questions Vocabulary
How are the Pauli exclusion principle, the aufbau principle, and Hund’s rule used to write electron configurations?
How do electron-dot structures represent an atom’s valence electrons?
Vocabulary
electron configuration
aufbau principle
Pauli exclusion principle
Hund’s rule
valence electron
electron-dot structure
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Electron Configuration