Modern periodic table is the arrangement of elements on the basis of increasing atomic number in 7 horizontal rows and 18 vertical columns. Horizontal rows are termed as Periods while the vertical columns are termed as Groups.
Elements present in Group 1, 2,13 to 18, and Period 3 of the periodic table are termed as typical elements. For example, Magnesium (Mg) and Aluminium (Al).
Elements present in Group 1 of the periodic table, except for Hydrogen (H), are termed as alkali metals. For example, Cesium (Cs).
Since Sodium (Na) belongs to group 1 of the periodic table, it is classified as an alkali metal.