Boron has two naturally occurring isotopes: boron -10 (19.8% abundance, mass 10.013 amu ) and born -11 (80.2% abundance, mass of 11.009 amu). what is the average atomic mass of boron? show work   

Hello!

To find the average atomic mass of boron, we need to use this formula:

Average Mass = (mass of isotope #1)(percent abundance) + (mass of isotope #2)(percent abundance) + ...

Before we use the formula, we need to convert the percentages into decimals. Remember that all percentages are out of 100, so, we divide the percent by 100 to get it into decimal form.

19.8 / 100 = 0.198

80.2 / 100 = 0.802

Average Mass = (10.013 amu)(0.198) + (11.009 amu)(0.802)

Average Mass = 1.98 amu + 8.83 amu

Average Mass = 10.81 amu

Therefore, the average atomic mass of boron is 10.81 amu.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.