1.1.3 Electron Configuration

• What does the electron configuration of an atom describe?

  Arrangement of electrons
• The general format for electron configuration is $1s^{2}$
• Match the element with its electron configuration:

  Hydrogen ↔️ $1s^{1}$

  Helium ↔️ $1s^{2}$

  Lithium ↔️ $1s^{2} 2s^{1}$

  Oxygen ↔️ $1s^{2} 2s^{2} 2p^{4}$
• What is the purpose of quantum numbers?

  Describe electron state
• The principal quantum number (n) determines the energy
• What does the azimuthal quantum number (l) determine?

  Shape of orbital
• The spin quantum number can only have two values: +1/2 or -1/2.
• What does the Aufbau principle state?

  Electrons fill lowest energy first
• The order of filling atomic orbitals according to the Aufbau principle is $1s < 2s$
• Arrange the following sub-shells in the order they are filled according to the Aufbau principle:

  1️⃣ 1s

  2️⃣ 2s

  3️⃣ 2p

  4️⃣ 3s

  5️⃣ 3p

  6️⃣ 4s

  7️⃣ 3d
• What does Hund's rule state about electron configuration within a sub-shell?

  Electrons singly occupy orbitals
• Hund's rule maximizes the overall spin multiplicity
• All unpaired electrons in a sub-shell must have the same spin according to Hund's rule.
• What is the electron configuration of carbon (atomic number 6)?

  $1s^{2} 2s^{2} 2p^{2}$
• In the 2p sub-shell of oxygen, the electron configuration is $↑↓ \, ↑ \, ↑$
• When applying Hund's rule, electrons first fill each orbital singly
• All unpaired electrons in a sub-shell must have the same spin according to Hund's rule
• The electron configuration of carbon is $1s^{2} 2s^{2} 2p^{2}$
• In the 2p sub-shell of carbon, the two electrons occupy the same orbital

  False
• What is the atomic number of oxygen?

  8
• The electron configuration of oxygen is $1s^{2} 2s^{2} 2p^{4}$
• In the 2p sub-shell of oxygen, electrons fill orbitals individually before doubling up
• Match the principle with its focus:

  Aufbau Principle ↔️ Filling lowest energy levels first

  Pauli Exclusion Principle ↔️ Maximum two electrons per orbital

  Hund's Rule ↔️ Maximizing spin multiplicity
• Following Hund's rule leads to the most stable and energetically favorable electron configurations
• What does Hund's rule state about the spin of unpaired electrons?

  They must be the same
• Electrons must double up in an orbital before filling each orbital singly according to Hund's rule

  False
• Order the principles by their focus from lowest to highest energy: Aufbau, Pauli Exclusion, Hund's

  1️⃣ Aufbau Principle

  2️⃣ Pauli Exclusion Principle

  3️⃣ Hund's Rule
• Hund's rule ensures the most stable and energetically favorable electron configurations
• The electron configuration describes the arrangement of electrons in an atom's shells
• What is the general format of an electron configuration?

  1s^{2} 2s^{2} 2p^{6}3s^{2} 3p^{6} 4s^{2} 3d^{10}...</latex>
• The electron configuration of hydrogen is $1s^{2}$


  False
• What is the atomic number of helium?

  2
• The electron configuration of helium is $1s^{2}$
• Lithium has an atomic number of 3 and its electron configuration is 1s^{2} 2s^{1}</latex>
• What is electron configuration used to describe?

  Arrangement of electrons
• Electron configuration specifies which orbitals are occupied and their energy levels.
• Electron configuration determines the chemical properties of an atom.
• Match the element with its electron configuration:

  Hydrogen ↔️ $1s^{1}$

  Helium ↔️ $1s^{2}$

  Lithium ↔️ $1s^{2} 2s^{1}$
• What is the electron configuration of Oxygen?

  1s^{2} 2s^{2} 2p^{4}</latex>
• Arrange the four quantum numbers in the order they describe an electron's state:

  1️⃣ Principal quantum number (n)

  2️⃣ Azimuthal quantum number (l)

  3️⃣ Magnetic quantum number (m_l)

  4️⃣ Spin quantum number (m_s)