Electrons In Atoms

Page: 6, Ryleigh Purser

Electron Configuration

The coordinates (“address”) for where electrons are

located within an atom;

includes the energy level, sublevel, orbital, and spin of

each electron

Electron configurations for ions

Losing electrons = positive ions (Na+1)

Gaining electrons = negative ions (Cl-1)

Add or subtract the correct number of electrons from the

highest energy level

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Electron Configurations are the way electrons are

arranged in various orbitals around the nuclei of atoms.

These rules tell us how to create orbital notation:

Aufbau principle - electrons enter the lowest energy

first. This causes difficulties because of the overlap of orbitals of

different energies.

Pauli Exclusion Principle - at most 2 electrons per

orbital - different spins

  • "No two electrons in an atom can have the same four quantum numbers."
  • To show the different direction of spin, a pair in the same orbital

Hund’s Rule – Every orbital in a sublevel is singly occupied before any orbital

is doubly occupied.

  • Also known as “the school bus rule”
  • Electrons individually fill empty orbitals before pairing up

Heisenberg's Rule - “One cannot simultaneously determine both the position and momentum of an electron.”

  • You can find out where the electron is, but not where it is going.
  • You can find out where the electron is going, but not where it is!

All of the electrons in singly occupied orbitals have the same

spin (to maximize total spin).

Orbital Notation

Orbital Notation is a drawing of the Electron Configuration using arrows. It is very useful in determining electron grouping and quantum numbers.

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  • Principal quantum number
  • Represents the main energy level of an electron
  • Maximum # of e- in an energy level = 2n2


  • The 2nd quantum number
  • Describes the orbital shape within an energy level
  • Number of orbital shapes possible in energy level = n (same as principle quantum number)
  • n = 1 has 1 shape, n = 2 has 2 shapes, etc...


  • The 3rd quantum number
  • Describes the orientation of the orbital in space (on x, y, or z axis)


  • The 4th quantum number
  • Describes the spin of electrons in orbitals
  • Ground state: lowest energy arrangement of electrons
  • spin up or spin down