What do periods and groups represent in the periodic table?

Periods and groups in the periodic table represent horizontal rows and vertical columns respectively, indicating different chemical properties.

In the periodic table, periods are the horizontal rows that run from left to right. There are seven periods in total, each representing a different energy level. The period number of an element signifies the highest energy level an electron in that element possesses. As you move from left to right across a period, the atomic number of the elements increases. This means that each element in a period has one more proton in its nucleus and one more electron in its outer shell than the element before it. This increase in atomic number across a period leads to a change in properties of the elements. For example, elements at the start of a period are usually metals, while those at the end are non-metals.

Groups, on the other hand, are the vertical columns in the periodic table. There are 18 groups in total. Elements in the same group have the same number of electrons in their outer shell, also known as valence electrons. These valence electrons determine the chemical behaviour of an element, so elements in the same group tend to have similar chemical properties. For instance, all elements in Group 1 (the alkali metals) are highly reactive, while those in Group 18 (the noble gases) are very unreactive.

In summary, periods and groups in the periodic table are a way of organising elements based on their atomic structure and chemical properties. Understanding these patterns can help you predict how different elements will behave in chemical reactions.