An element has two naturally occurring Isotopes. The mass numbers of these isotopes are 109.00 u and 111.00 u, with natural
abundances of 20% and 80%, respectively. Calculate its average atomic mass, Report your answer to 2 decimal places.

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answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.