Three naturally occurring isotopes of carbon exist: The atomic mass of carbon is 12.01 amu. Which of the three carbon isotopes is most abundant in nature?
A) carbon-12
B) carbon-13
C) carbon-14
D) all three occur with equal abundance
The correct answer and explanation is :
The correct answer is:
A) carbon-12
Explanation:
Carbon has three naturally occurring isotopes: carbon-12 (¹²C), carbon-13 (¹³C), and carbon-14 (¹⁴C). The atomic mass of carbon, as given in the problem, is 12.01 atomic mass units (amu). This value is the weighted average of all naturally occurring isotopes of carbon based on their relative abundance.
Why Carbon-12 is the Most Abundant?
- Proximity to Atomic Mass:
- The atomic mass of carbon is 12.01 amu, which is very close to 12 amu, the exact mass of carbon-12.
- This suggests that carbon-12 is by far the most abundant isotope, as it has the greatest influence on the weighted average.
- Relative Abundance of Carbon Isotopes:
- Carbon-12 makes up about 98.93% of all carbon found in nature.
- Carbon-13 is much less common, with a natural abundance of about 1.07%.
- Carbon-14 is extremely rare (less than 0.0000000001%) and is primarily used in radiocarbon dating.
- Stability:
- Carbon-12 and carbon-13 are both stable isotopes, meaning they do not undergo radioactive decay.
- Carbon-14, however, is radioactive and decays over time with a half-life of about 5,730 years. Its presence in nature is due to continuous production in the atmosphere via cosmic ray interactions with nitrogen.
Since the atomic mass of carbon is very close to 12, and carbon-12 has the highest percentage, we can confidently say that carbon-12 is the most abundant isotope of carbon in nature.
Image:
Here is an image representing the three isotopes of carbon:
