Electron configuration

• The principal quantum number indicates the shell occupied by the electrons
• A shell is a group of orbitals with the same principal quantum number
• The 1st shell can hold 2 electrons
• The 2nd shell can hold 8 electrons
• The 3rd shell can hold 18 electrons
• The 4th shell can hold 32 electrons
• An orbital is a region around the nucleus that can hold up to two electrons with opposite spins
• An orbital can hold 2 electrons
• The 4 types of orbitals are:

  • s orbital
  • p orbital
  • d orbital
  • f orbital
• The shape of an s-orbital is spherical
• The shape of a p-orbital is dumb-bell shape
• A S subshell has 1 orbital and can hold 2 electrons
• A P subshell has 3 orbitals and can hold 6 electrons
• A D subshell has 5 orbitals and can hold 10 electrons
• An F subshell has 7 orbitals and can hold 14 electrons
• When using 'electrons in box' representation, arrows are used to represent the electrons
• The letter 'n' is used to represent the shell number
• S orbital is present from n = 1 shell onwards
• P orbital is present from n = 2 shell onwards
• D orbital is present from n = 3 shell onwards
• F orbital is present from n = 4 shell onwards
• Rules for arranging electrons in a shell:

  • Electrons are added one at a time
  • Lowest available energy level is filled first
  • Each energy level must be filled before the next one can fill
  • Each orbital is filled singly before pairing
  • 4s is filled before 3d
• 4s orbital fills before 3d orbital because 4s orbital has a lower energy
• When an atom becomes a positive ion, it loses electrons in the highest energy levels
• What is the charge of a proton? +1
• What is the charge of a neutron? 0
• What is the charge of an electron? -1
• What is the relative mass of an electron?

  1/2000
• what is the relative mass of a proton?

  1
• What is the relative mass of a neutron?

  1
• How to calculate neutrons?

  Subtract the atomic number from the atomic mass.