2.4.1 Electron configuration

• What does the Aufbau principle describe in chemistry?

  Order of filling orbitals
• Each orbital can hold a maximum of 2 electrons with opposite spin
• Arrange the orbitals in order of increasing energy level according to the Aufbau principle.

  1️⃣ 1s

  2️⃣ 2s

  3️⃣ 2p

  4️⃣ 3s

  5️⃣ 3p

  6️⃣ 4s

  7️⃣ 3d
• Why does Hund's rule result in unpaired electrons with parallel spin?

  Increases atomic stability
• Without the Pauli Exclusion Principle, all 6 electrons could occupy the 2p orbitals without spin restriction
• What determines the electron configuration of an atom?

  Atomic orbitals
• Electrons fill orbitals in order of increasing energy
• Arrange the following atomic orbitals in the order they are filled according to the Aufbau principle:

  1️⃣ 1s

  2️⃣ 2s

  3️⃣ 2p

  4️⃣ 3s

  5️⃣ 3p
• Hund's rule maximizes the multiplicity of an atom by ensuring unpaired electrons have parallel spin.


  True
• What is the electron configuration of a chromium (Cr) atom when Hund's rule is applied?

  [Ar] 3d^5 4s^1
• Without the Pauli Exclusion Principle, electrons in the 2p orbitals would all have the same spin.


  True
• What does the Pauli Exclusion Principle state about the maximum number of electrons in an orbital?

  2 electrons with opposite spin
• Electrons first fill the 1s orbital, which has the lowest energy.


  True
• Arrange the following orbitals in the correct order of increasing energy:

  1️⃣ 3p

  2️⃣ 4s

  3️⃣ 3d

  4️⃣ 4p

  5️⃣ 5s
• Cations are formed by losing electrons from the highest energy level.
• Match the atom/ion with its correct electron configuration:

  Neutral Sodium (Na) ↔️ 1s^2 2s^2 2p^6 3s^1

  Sodium Cation (Na^+) ↔️ 1s^2 2s^2 2p^6
• The Pauli Exclusion Principle states that each orbital can hold a maximum of 2 electrons with opposite spin.
• What is the term for the number of unpaired electrons in an atom according to Hund's rule?

  Multiplicity
• Electrons fill orbitals in order of increasing energy level, starting with the 1s orbital.


  True
• What does Hund's rule state regarding the filling of degenerate orbitals?

  Singly with parallel spin
• Hund's rule maximizes the multiplicity
• The Pauli Exclusion Principle states that each orbital can hold two electrons with the same spin.

  False
• Match the principle with its description:

  Aufbau principle ↔️ Order of filling orbitals

  Pauli Exclusion Principle ↔️ 2 electrons with opposite spin

  Hund's rule ↔️ Electrons occupy singly with parallel spin
• The Aufbau principle describes the order in which electrons fill atomic orbitals in an atom.


  True
• What is the maximum number of electrons an atomic orbital can hold according to the Pauli Exclusion Principle?

  Two
• Why is understanding the Aufbau principle crucial?

  Chemical properties
• Match the orbital filling scenario with the correct description:

  2p orbitals without Hund's rule ↔️ 2p^6 (all paired)

  2p orbitals with Hund's rule ↔️ 2p^3 (3 unpaired)
• The Pauli Exclusion Principle states that each atomic orbital can hold a maximum of 2 electrons with opposite spin
• Steps to write the electron configuration for a neutral atom:

  1️⃣ Fill the lowest energy 1s orbital

  2️⃣ Fill the 2s orbital

  3️⃣ Fill the 3 degenerate 2p orbitals

  4️⃣ Continue filling in order of increasing energy
• The order of filling orbitals in electron configurations follows the Aufbau principle.
• What is the next orbital filled after 2s in the order of increasing energy?

  2p
• What does Hund's rule state about filling degenerate orbitals?

  Electrons occupy them singly with parallel spin
• Anions are formed by adding electrons to the lowest available orbital.


  True
• What does the Aufbau principle describe about atomic orbitals?

  The order of filling
• Hund's rule maximizes the multiplicity of an atom by ensuring unpaired electrons have parallel spin.

  True
• What does the Pauli Exclusion Principle state about electrons in an atomic orbital?

  2 electrons with opposite spin
• Why is understanding the Aufbau principle crucial?

  Determining electron configurations
• What is the electron configuration of 2p orbitals according to Hund's rule?

  2p^3
• What is the observed electron configuration of chromium (Cr) according to Hund's rule?

  [Ar] 3d^5 4s^1
• Without the Pauli Exclusion Principle, each 2p orbital could hold more than 2 electrons.

  True