| Group no. | Name of the element name | Elements | Valence shell configuration | Valence electrons | Valency |
| 1 (IA) | Alkali metal family | Li Fr | ns' | 1 | 1 |
| 2 (IIA) | Alkali earth metal family | ||||
| 13 (IIIA) | Boron family | ||||
| 14 (IVA) | Carbon family | ||||
| 15 (VA) | Nitrogen family | 16(VIA) | Oxygen family or (Chalcogen family) | ||
| 17(VIIA) | Halogen family | ||||
| 18 (VIIIA) | Noble gas family |
The horizontal rows in the periodic table are called periods. There are seven periods in the modern periodic table. These periods are represented by Arabic numerals I through 7.
1. The number of main shells present in the atom of particular element decides to which period it belongs. For example, hydrogen (H) and helium (He) atoms contain only one main shell (K). Therefore they belongs to period-1. Similarly, the elements Li, Be, B, C, N, O, F and Ne contain two main shells (K and L) in their atoms. Therefore they belong to period-2
2. The number of elements in period depend on how electrons are filled into various shells. Each period starts with a new main shell 's' subshell.