🔬 SCIENCE — Periodic Table Element Symbol and Name An element symbol is one or two letters that stand for an element. The first letter is always capitalized, and if there is a second letter, it is lowercase. For example, H means Hydrogen and He means Helium. Groups and Periods Groups are the vertical columns that go up and down. Elements in the same group share similar properties. There are 18 groups in total. Periods are the horizontal rows that go left to right. Properties change gradually as you move across a period. There are 7 periods in total. The First 20 Elements in Order 1 H Hydrogen 2 He Helium 3 Li Lithium 4 Be Beryllium 5 B Boron 6 C Carbon 7 N Nitrogen 8 O Oxygen 9 F Fluorine 10 Ne Neon 11 Na Sodium 12 Mg Magnesium 13 Al Aluminum 14 Si Silicon 15 P Phosphorus 16 S Sulfur 17 Cl Chlorine 18 Ar Argon 19 K Potassium 20 Ca Calcium