please help me please

Question

Ms. Kubena discovered a new element and named it Kubena (Ku) after herself. This new element has two naturally occurring isotopes. One has a mass number of 65 and a percent abundance of 23%. The other has a mass number of 67 and a percent abundance of 77%. This data is summarized in the table below. 

Calculate the average atomic mass that will appear on the periodic table for this new element. SHOW YOUR WORK and round to two decimal places.  

BoldItalicUnderline

Answer 1

Hello, Aseel,

You want the weighted average of the two isotopes, so multiply their mass times their percent abundance to calculate the mass due to each isotope, and then add the two for the weighted mass that would appear on the table. You'll note that if the abundance of one isotope were 100%, the result would be the mass of only that isotope. The weighted average is simply a good approximation for the average mass of this element when collected from the Earth. It may not apply elsewhere in the universe.

Bob