Electronic Structure of Atoms

• Main energy level or shell


  • Region of space about a nucleus that contains electrons
  • have approximately the same energy and that spend most of their time approximately the same distance from the nucleus
• Sublevel or subshell


  Region of space within an electron shell that contains electrons that have the same energy
• Electron orbital or atomic orbital

  • electron subshell where an electron with a specific energy is most likely to be found
• Electron shells

  • Electron energy increases as the distance of the electron shell from the nucleus increases
  • The maximum number of electrons that an electron shell can accommodate varies; the higher the shell number (n), the more electrons that can be present
• Subshells


  • "The number of subshells within a shell" is the same as the shell number
  • Subshells within a shell differ in size (the maximum number of electrons they can accommodate) and energy
  • Subshell size (type) is designated using the letters s, p, d, and f
• Subshell types


  • s
  • p
  • d
  • f
• Quantum numbers


  Used to describe the distribution of electrons in hydrogen and other atoms
• Principal quantum number (n)


  • "Refers to the main energy level of an orbital" and can have integral values 1, 2, 3, and so forth
  • Relates to the average distance of the electron from the nucleus in a particular orbital
• Angular momentum quantum number or azimuthal quantum number (l)


  • Represents energy sublevels and tells us the shape of the orbitals
  • For a given value of n, l has possible integral values from 0 to (n - 1)
• Magnetic quantum number (ml)


  • Describes the orientation of the orbital in space
  • Within a subshell, the value of ml depends on the value of l
  • The ml can have integral value from -l to +l, including 0
• Spin quantum number (ms)


  • Describes the spin of electron
  • Can be +1/2 (upward arrow) or -1/2 (downward arrow)
• Assigning electrons to orbitals

  1. Aufbau principle: "electrons subshells are filled" in order of increasing energy

  2. Hund's rule: "electrons occupy the orbitals of a subshell such that each orbital acquires one electron" before any orbital acquires a second electron, all with the same spin

  3. Pauli exclusion principle: ""no more than two electrons may exist in a given orbital," and they must have opposite spins
• Electron configuration


  Describes how the electrons are distributed among the subshells
• Orbital diagram


  Notation that shows how many electrons an atom has in each of its occupied electron orbitals