When filling an orbital diagram, remember the following:

1. Fill the lowest energy orbital that is available.

2. Place one arrow in each orbital of the same energy level before putting pairs of arrows in any orbital at that level. All the single electrons should be shown as having the same spin. In other words, all of the single arrows representing electrons in different orbitals at the same energy level should point up.

3. If two electrons share an orbital, they must have opposite spins. No more than two electrons can share an orbital.

1s orbital is closest to the nucleus and has the lowest energy

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​The closer an orbital is to the atomic nucleus, the lower its energy

Within an energy level, the higher the azimuthal quantum number the more energy in the orbital. The 2p orbitals (azimuthal number 1) are slightly higher in energy than the 2s orbitals (azimuthal number 0).

​The differences between the energy levels generally decrease further from the atomic nucleus.