Describe what an isotope is and explain how it relates to the masses you see for each element on the periodic table. ( why are the masses decimals instead of whole numbers). What is the difference between an isotope and a ion.

Isotopes are atoms of the same element with different mass numbers(sum of protons) but same atomic number(number of protons).

Mass of an element in the periodic table is the average of masses of its isotopes.

The atomic masses of most elements are not whole numbers because they are a weighted average of the mass numbers of the different isotopes of that element with  respect to their abundances in nature.

An isotope is a neutral atom while an ion is a charged particle.

Step-by-step explanation

An isotope refers to one of more species  of a chemical element with the same atomic number,same position  in the periodic table  and nearly identical chemical behaviour but with different physical properties .    

Number of neutrons for given elements can vary and therefore isotopes differ only in their number of neutrons.The sum of the number of protons and the number of neutrons determines the element's mass number.

The atomic masses of most elements are not whole numbers because they are a weighted average of the mass numbers of the different isotopes of that element with  respect to their abundances in nature.

R.A.M=[(Mass of isotope 1  x % abundance of isotope 1 )+( mass of isotope 2 x % of isotope 2) +..............]/100%

An isotope is an atom with the same number of protons but different number of neutrons while an ion is any atom or groups of atoms that bear one or more positive or negative electrical charges.