# Electrons In Atoms

## 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

## RULES

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.

## PRINCIPLE QUANTUM NUMBER: N

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

## ANGULAR QUANTUM NUMBER: L

• 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...

## MAGNETIC QUANTUM NUMBER: M

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

## QUANTUM SPIN: S

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