The periodic table is a tabular display of the chemical elements, organised on the basis of their properties. Elements are presented in increasing atomic number. The main body of the table is a 18 × 7 grid, with gaps included in to keep elements with similar properties together, such as the halogens and the noble gases. These gaps form four distinct rectangular areas or blocks. The f-block is not included in the main table, but rather is usually floated below, as an inline f-block would make the table impractically wide. The periodic table accurately predicts the properties of various elements and the relations between properties. As a result, it provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences.