YO HELP PLS When the elements on the periodic table are arranged by increasing atomic numbers, the atomic mass generally increases as the atomic number increases. For some elements, however, the atomic mass of the element is lower than the atomic mass for the element that came before it. Explain how this could be possible.

The atomic number of an atom is the number of protons it contains. All the atoms of a particular element have the same atomic number (number of protons). ... The mass number of an atom is the total number of protons and neutrons it contains. The mass number of an atom is never smaller than the atomic number.

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