Periodic Table Periods
The periodic table is composed of horizontal rows called periods. There are 7 periods in the modern periodic table. The atomic numbers increase from left to right in each period. Elements in the same period have the same number of electron shells. Though they are in the same period, elements in the same period do not share similar chemical properties. Each period ends with an element known as a noble gas.
- Period 1 - contains 2 elements hydrogen (H) and helium (He)
- Period 2 - contains 8 elements lithium (Li) through neon (Ne)
- Period 3 - contains 8 elements sodium (Na) through argon (Ar)
- Period 4 - contains 18 elements potassium (K) through krypton (Kr)
- Period 5 - contains 18 elements rubidium (Rb) through xenon (Xe)
- Period 6 - contains 32 elements caesium (Cs) through radon (Rn). Period 6 also includes the f-block, with the lanthanides.
- Period 7 - is not complete, includes gaps. All elements of period 7 are radioactive. Period 7 also includes the f-block, with the actinoids.