Boron exists in two isotopes, boron-10 and boron-11. Based on the atomic mass, which isotope should be more abundant?

Answer 1

Boron-11

The atomic mass of boron is 10.81 u. And 10.81 u is a lot closer to 11u than it is to 10u, so there must be more of boron-11. To convince you fully, we can also do a simple calculation to find the exact proportion of boron-11 using the following formula:

#((10 u)(x)+(11 u)(1-x))/(100%)=10.81u#

Where u is the unit for atomic mass and x is the proportion of boron-10 out of the total boron abundance which is 100%.

Solving for x we get:

#11u-ux=10.81u# #0.19u=ux# #x=0.19# #1-x=0.81#

And thus the abundance of boron-11 is roughly 81%.

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Answer 2

Naomi Aronson

Since boron-11's atomic mass is closer to that of boron, which is roughly 10.81, it should be more abundant.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.