CHEM2

• Importance of electrons in determining the chemical properties of an element:

  • Valence Electrons and Reactivity
  • Chemical Bonding and Chemical Reactions
  • Ion Formation
  • Molecular Structure
  • Electronegativity
  • Chemical Families
  • Chemical Reactivity Trends
  • Material Properties
• Three rules in electron configuration:

  1. Aufbau Principle:

  • Electrons are first placed in the orbital of the lowest energy, then the orbital of the next lowest energy and so on

  2. Pauli Exclusion Principle:

  • Each orbital can only hold a maximum of 2 electrons
  • If there are 2 electrons in the same orbital, they must have opposite spins

  3. Hund's Rule:

  • Electrons are added to orbitals in a subshell singly and with parallel spins before orbitals are occupied in pairs
• Standardized notation for writing electron configurations:

  • Energy level and the type of orbital are written first
  • Followed by the number of electrons present in the orbital written in superscript
  • Example: the electronic configuration of carbon (atomic number: 6) is 1s2 2s2 2p2
• An electron is a stable subatomic particle with a negative electrical charge
• Electrons are found outside the nucleus
• The mass of an electron is 9.10938 x 10-31 kg, which is about 1/836 the mass of a proton
• Importance of electrons in determining the chemical properties of an element:
• Electron configuration determines how an element will react chemically
• Electron Configuration:
• The number of subshells in a shell is equal to the shell number
• The first subshell, s, has 1 orbital
• Each successive subshell adds 2 more orbitals (1, 3, 5, 7, etc.)
• Each orbital can hold 2 electrons of opposite spin
• An atom with n=3 indicates all subshells and orbitals for n<3: 1s, 2s, 2p, 3s, 3p, 3d
• Writing Electron Configuration:
• Aufbau Principle: Electrons are first placed in the orbital of the lowest energy, then the orbital of the next lowest energy, and so on
• Pauli Exclusion Principle: Each orbital can only hold a maximum of 2 electrons. If there are 2 electrons in the same orbital, they must have opposite spins
• Hund's Rule: Electrons are added to orbitals in a subshell singly and with parallel spins before orbitals are occupied in pairs
• Standardized notation for electron configurations: energy level and the type of orbital are written first, followed by the number of electrons present in the orbital written in superscript
• Example: The electronic configuration of carbon (atomic number: 6) is 1s2 2s2 2p2