The elements are arranged in order of increasing atomic mass in the periodic table. However, it's important to note that the modern periodic table organizes the elements based on their atomic number, which represents the number of protons in an atom's nucleus. The atomic number determines the element's identity, and elements are ordered in ascending order of their atomic numbers.
That being said, the atomic mass of elements is still included in the periodic table, usually listed below the element's symbol. The atomic mass is the average mass of all the naturally occurring isotopes of an element, taking into account their relative abundance.
In earlier versions of the periodic table, elements were arranged based on their atomic mass, and this arrangement led to the identification of periodicity and the development of the periodic law. However, the discovery of isotopes and the realization that atomic number has more fundamental significance led to the current arrangement of elements based on atomic number.
So, while the periodic table is primarily organized by atomic number, the atomic mass is still provided as additional information for each element.