A period 2 element is an element in the second period (row) of the periodic table. Period 2 has eight elements: lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon. Their atomic numbers go from 3 to 10.

Period 2 elements have electrons in the first two electron shells. The first electron shell is always full. The second electron shell (valence electrons) fills when atomic number gets bigger. Two electrons join the 2s orbital, and six electrons join the 2p orbitals.

These atoms can become stable in two ways:

• They can lose electrons so the second electron shell is empty. Lithium, beryllium, and sometimes boron do this.
• They can gain electrons so the second electron shell is full, with 8 electrons. Fluorine, oxygen, nitrogen, and carbon usually do this.