ATOMS

• Bohr's planetary model


  Electrons are most probably found in a three-dimensional space around the nucleus, known as the orbital
• Schrödinger was able to formulate this using complicated mathematical techniques which require advanced knowledge of calculus to solve
• Solutions to Schrödinger's equation are known as quantum numbers, and to completely describe a certain electron in an atom, the four quantum numbers must be specified
• Principal Quantum Number (n)


  Refers to the main energy levels (or shells) of an orbital
• Principal Quantum Number (n)


  • The first circle corresponds to n = 1, and the electrons occupying the n = 1 principal QN can be found anywhere within the space enclosed by the said energy level
  • The principal quantum number can take values from 1 to ∞, and the higher the value of n, the higher the energy of the orbital, and the farther the electron from the nucleus
  • The higher the n value, the larger the atom is
• Azimuthal Quantum Number (ℓ)


  Pertains to the energy sublevels or subshells of the orbital, and has something to do with the shape of the orbital
• Azimuthal Quantum Number (ℓ) values and corresponding orbital shapes

  • ℓ = 0 (s orbital, spherical)
  • ℓ = 1 (p orbital, dumb-bell)
  • ℓ = 2 (d orbital, not easily visualized)
  • ℓ = 3 (f orbital, not easily visualized)
  • ℓ = 4 (g orbital)
• Magnetic Quantum Number (mℓ)

  Tells us about the orientation of orbitals in space
• Magnetic Quantum Number (mℓ) values

  • -ℓ to +ℓ, including zero
• Spin Quantum Number (ms)


  Pertains to the electron spin, which can only be either clockwise or counterclockwise
• Spin Quantum Number (ms) values

  • +½ and -½
• We can use these quantum numbers to assign electronic configurations to each electron in a multi-electron system, but some rules/principles must be followed
• Electron configuration


  The distribution of electrons among the various orbitals in an atom, molecule, or ion
• To write electron configuration correctly, you need to know the number of electrons present, the number of electrons each orbital can occupy, and the correct ordering of the orbitals
• Maximum number of electrons each orbital can occupy

  • s orbitals: 2 electrons
  • p orbitals: 6 electrons
  • d orbitals: 10 electrons
  • f orbitals: 14 electrons
• Aufbau principle


  As a proton is being added one by one to the nucleus to build up the element, electrons are likewise added to the orbital
• (n + ℓ) rule

  The added electrons must occupy an orbital with a lower (n + ℓ) value first, i.e. the added electrons should occupy the orbital with lower energy first
• Hund's rule of multiplicity

  Every orbital in a subshell is singly occupied with one electron before any orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin
• Pauli's exclusion principle


  No two electrons can have the same set of four quantum numbers