What element has 3 energy levels/orbitals and 5 valence electrons in its outer energy level?  

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t-nez eNotes educator| Certified Educator

The element that has three energy levels and five valence electrons in its outer level is phophorous, atomic number 15. Each row or period of the periodic table corresponds to a principal energy level. All elements in the third period have three electron energy levels and have their valence electrons in the third level. Orbitals are sub-levels within the principal energy level, so the word orbital isn't used interchangeably with energy level. 

The number of valence electrons increases by one with each element in a period. Group 1 elements have one valence election, Group 2 elements have two, Group 13 (also known as IIIA) have three, Group 14 (IVA) have four, Group 15 (VA) have five and so on. Phosphorous is the 5th element from the left in the third period so it has five valence electrons.