When moving energy levels, electrons emit packets of energies called photons. They behave both like a particle and a wave. Below are equations: $c=\lambda f$ $\lambda$ is wavelength and $f$ is frequency. $\Delta E_{electron}=\Delta E_{photon}=hf$ , $h$ is the planks constant.

Some principles

Heisenberg’s Uncertainty Principle Pauli Exclusion Principle

Orbitals

Areas where there is a 90% of finding the electron. They hold 2 electrons. $spdf$ Principal quantum number: Number of energy levels

Filling orbitals

Go from bottom up. Fill in single arrows with same spin across the orbital before refilling. There are Exceptions to Filling orbitals.