After the first level has two electrons, the next electron goes into the second level. 2nd Period: Lithium to neon—Electrons go into the second level. After the second level has 8 electrons, the next ...

The zigzag, staircase, line in the diagram of the periodic table above separates the metals, on the left, from non-metals, on the right. Hydrogen is a non-metal, but it is often put in the middle.

There are 118 elements in the periodic table, each with a unique symbol and atomic number. Symbol: A one or two-letter abbreviation used to represent the element. Atomic number: The number of ...