The periodic table is organized into periods and groups, which help categorize the elements based on their properties. Periods refer to the 7 horizontal rows of the table, starting from the left. For instance, the first row includes hydrogen (H) and helium (He), making it Period 1. The second row, which includes lithium (Li) to neon (Ne), is Period 2, and this pattern continues through to Period 7. Notably, the periodic table is dynamic; while it currently contains 7 periods, advancements in technology and exploration may lead to the discovery of new elements, potentially adding more periods in the future.
In contrast, groups are the vertical columns of the periodic table, also known as families or series. There are 18 groups, each containing elements that share similar chemical properties due to their electron arrangements. For example, Group 1, which includes hydrogen (H) down to francium (Fr), is known as the alkali metals, while Group 2, from beryllium (Be) to radium (Ra), is referred to as alkaline earth metals. Other notable groups include the nitrogen group (Group 15), the chalcogens (Group 16), the halogens (Group 17), and the noble gases (Group 18). The term "noble gases" reflects their stability, although some can react under certain conditions.
Additionally, there are two special rows at the bottom of the periodic table: the lanthanides, which follow lanthanum (La), and the actinides, which follow actinium (Ac). Understanding the structure of the periodic table, including the distinction between periods and groups, is essential for grasping the relationships and behaviors of different elements in chemistry.