Question

1. naturally - occurring element. it exists in three isotopic forms: 5 - 83 (127.877 amu, 92.23% abundance), j - 23 (128.905 amu, 4.75% abundance) and j - 30 (129.904 amu, 3.02% abundance). calculate the average atomic mass. round your answer to the hundredths - place.
2. naturally - occurring iron contains 5.80% iron - 54, 91.66% iron - 56, 2.19% iron - 57 and 0.35% iron - 58. calculate the average atomic mass of iron. round your answer to the hundredths place.
3. the graph to the right shows part of the mass spectrum for a sample of an element. calculate the relative atomic mass. what is the identity of the element?
4. gallium has two naturally - occurring isotopes, ga - 69 (68.926 amu) and ga - 71 (70.925 amu). if the average atomic mass of gallium is 69.72 amu, what is the percent abundance of each isotope?
5. describe the difference between mendeleevs and moseleys periodic organization and why the current periodic table is organized by atomic number.

Explanation:

Step1: Identify the problem type

These are chemistry - related problems about calculating average atomic masses and percent abundances.

Step2: For calculating average atomic mass

The formula is $\text{Average atomic mass}=\sum_{i}( \text{Isotope mass}_i\times\text{Percent abundance}_i)$. For example, if we have isotope 1 with mass $m_1$ and percent abundance $p_1$ (in decimal form) and isotope 2 with mass $m_2$ and percent abundance $p_2$, then $\text{Average atomic mass}=m_1p_1 + m_2p_2$.

Step3: For finding percent abundances

Let the percent abundance of one isotope be $x$ (in decimal form), then the other is $1 - x$. We set up an equation using the average - atomic - mass formula and solve for $x$.

Step4: For describing the difference between Mendeleev and Moseley

Mendeleev arranged elements by atomic mass, while Moseley arranged them by atomic number. Moseley's arrangement fixed some of the inconsistencies in Mendeleev's table as it led to a more logical and periodic arrangement based on the fundamental property of the number of protons in the nucleus.

Answer:

12 - 15: Answers will depend on the specific values plugged into the average - atomic - mass and percent - abundance formulas.
16: Mendeleev arranged elements by atomic mass, Moseley by atomic number. Moseley's arrangement is more accurate as it is based on atomic number which is a more fundamental property of an element.