The atomic number of an element is defined as the number of protons in its nucleus. Since protons are discrete particles, the number of protons must always be a whole number. Consequently, atomic numbers can only be whole numbers (integers), not fractions or decimals.
An atomic number of 110.5 would imply that there is a non-integer number of protons, which is not physically possible. Therefore, no element can have an atomic number of 110.5. The highest atomic number that has been confirmed is 118, corresponding to the element oganesson (Og).
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