worksheet - isotopes and average atomic masses
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1. four isotopes of lead include lead - 204, lead - 206, lead - 207, and lead - 208. the average atomic mass of a lead atom is 207.2 amu. which isotope of lead is likely to be the most abundant?
2. what do all isotopes of an element have in common? different?
3. explain why carbon - 14 and nitrogen - 14 are not considered isotopes of each other.
4. write the atomic symbol (symbol notation) for the two isotopes of uranium(u), whose atomic number is 92. one isotope has 142 neutrons, and the other isotope has 146 neutrons.

Question

Accepted Answer

# 1.
## Brief Explanations:
The average atomic mass is closer to the mass of the most abundant isotope. Since the average atomic mass of lead is $207.2$ amu, which is closest to the mass of lead - 208 ($208$ amu).
# Answer:
Lead - 208

# 2.
## Brief Explanations:
Isotopes of an element have the same number of protons (atomic number). They have different numbers of neutrons (mass number = protons+neutrons, so mass numbers are different).
# Answer:
Same: Atomic number (number of protons). Different: Mass number (number of neutrons)

# 3.
## Brief Explanations:
Isotopes are atoms of the same element. Carbon - 14 is an atom of carbon ($Z = 6$) and nitrogen - 14 is an atom of nitrogen ($Z=7$). Since they are different elements (different atomic numbers), they are not isotopes.
# Answer:
They are atoms of different elements (different atomic numbers)

# 4.
## Brief Explanations:
The mass number $A$ of an atom is $A=Z + N$, where $Z$ is the atomic number and $N$ is the number of neutrons. For $Z = 92$:
- If $N = 142$, then $A=92 + 142=234$. The atomic symbol is $\ce{^{234}_{92}U}$
- If $N = 146$, then $A=92+146 = 238$. The atomic symbol is $\ce{^{238}_{92}U}$
# Answer:
$\ce{^{234}_{92}U}$ and $\ce{^{238}_{92}U}$

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