Chemistry Atomic Theory

Aufbau Principle

Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for.

Hund’s Rule

Electrons occupy equal-energy orbitals so that a maximum number of unpaired electrons results.

Pauli Exclusion Principle

An orbital can hold a maximum of two electrons. To occupy the same orbital, two electrons must spin in opposite directions.

1st energy level in an atom - how many electrons maximum?

2 - 1 orbital

2nd energy level - how many electrons maximum?

8 electrons - 4 orbitals

3rd energy level - how many electrons maximum?

18 electrons - 9 orbitals

How many electrons can one orbital hold at max?

2

Definition of quantum numbers

Numbers used to determine the most probable location of an electron

Quantum number n

Principal quantum number - tells us which energy level an electron is in

Quantum number l

Azimuthal number - tells us which sublevel within the energy level the electron is in

Quantum number m_l

Magnetic number - tells us which orbital within the sublevel the electron is in

Quantum number m_s

Spin number - tells us the direction of the spin (clockwise or counterclockwise)