An element has the following natural abundances and isotopic masses: 90.00% abundance with 19.99 amu, 1.18% abundance with 20.99 amu, and 8.82% abundance with 21.99 amu. calculate the average atomic mass of this element.(your answer should be to 5 significant figures)

average atomic mass = 20.178 a.m.u

Explanation:

Average atomic mass is calculated using the following formula:

Average atomic mass = abundance of isotope 1 × mass number of isotope 1 + abundance of isotope 2 × mass number of isotope 2 + ... + abundance of isotope n × mass number of isotope n

For the element described in the problem:

Average atomic mass = (90/100) × 19.99 + (1.18/100) × 20.99 + (8.82/100) × 21.99 = 20.178 a.m.u