Module 2.2.1- Electrons and bonding

• Number of electrons that can fill the first 4 shells

  2,8,18,32
• Principle quantum number


  Shell number or energy level number symbolized by n
• Shells are regarded as _______ and the energy _____ as the shell number increases

  energy levels, increases
• Atomic orbital


  A region around the nucleus that can hold up to two electrons with opposite spins
• s-orbitals


  spherical, 2 electrons

  
• p-orbitals


  orbitals that are dumbbell shaped and directed along the x, y, and z axes

  
• d-orbitals

  can hold a total of 10 electrons in 5 sub-shells
• Subshells


  different orbital types within a shell (s, p, d, f)

  
• Energy levels of subshells anomaly

  3d subshell is at a higher energy level than the 4s subshell. Therefore the 4s subshell fills in before the 3d subshells.The order is 3p 4s 3d

  
• Electron pairs with opposite spins


  electrons are negatively charged2 electrons in an orbital have opposite spins which help counteract the repulsion between negative charges of the two electrons

  
• Orbitals with the same energy are occupied singly first

  
• Example: electron configuration of Krypton (Z= 36)


  1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d10 4p6
• Example: electron configuration of Lithium (Z= 3)


  1s2 2s1
• Shorthand electron configuration


  Backtracking the last noble gas and writing what is left
• Shorthand electron configuration example Li

  [He] 2s1

  Since [He] = 2
• Ca -> Ca2+ electron configurationCa (Z= 20)


  Ca: 1s2 2s2 2p6 3s2 3p6 4s2

  Ca2+: 1s2 2s2 2p6 3s2 3p6
• Special rule of 4s subshell


  first IN

  first OUT
• Ni -> Ni2+Ni (Z= 28)


  Ni: 1s2 2s2 2p6 3s2 3p6 4s2 3d8

  Ni2+: 1s2 2s2 2p6 3s2 3p6 3d8

  4s2 empties first!!