A robot spacecraft returned samples from the planetesimal 98765 ALEKS, located in the outer Solar System. Mass-spectroscopic analysis produced the following data on the isotopes of ruthenium in these samples: mass relative isotope (amu) abundance 100, Ru 99.90 95.4% 99. Ru 98.91 4.6% Use these measurements to complete the entry for ruthenium in the Periodic Table that would be used on 98765 ALEKS. Round your entry for the atomic mass to 3 significant digits. ? Ar Caution: your correct answer will have the same format but not necessarily the same numbers as the entry for ruthenium in the Periodic Table we use here on Earth. Ru ☐

Mass spectrometric analysis showed that there are four isotopes of an unknown element having the following masses and abundances: Three elements in the periodic table that have atomic weights near these values are lanthanum (La), atomic number 57, atomic weight 138.9055; cerium (Ce), atomic number 58, atomic weight 140.115; and praseodymium (Pr), atomic number 59, atomic weight 140.9076. Using the data above, calculate the atomic weight, and identify the element if possible.

2-102 An element consists of 90.51% of an isotope with a mass of 19.992 amu, 0.27% of an isotope with a mass of 20.994 amu, and 9.22% of an isotope with a mass of 21.990 amu. Calculate the average atomic mass and identify the element.

Variations in average atomic mass may be observed for elements obtained from different sources. Lithium provides an example of this. The isotopic composition of lithium from naturally occurring minerals is 7.5% 6Li and 92.5% 7Li, which have masses of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium, recycled from a military source, was 3.75% 6Li (and the rest 7Li). Calculate the average atomic mass values for each of these two sources.