- In a group (also known as a family) is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table
- The modern explanation of the pattern of the table is that the elements in a group have similar configurations of the outermost electron shells of their atoms: as most chemical properties are dominated by the orbital location of the outermost electron
- In the periodic table of the elements, elements are arranged in a series of rows so that those with similar properties appear in vertical columns. This arrangement reflects the periodic recurrence of similar properties as the atomic number increases