Blues asked in Science & MathematicsChemistry · 1 month ago

# The atomic number of nitrogen is 7. The atomic mass is 14.01 amu. This means that___?

A.) A small percentage of nitrogen atoms have more than 7 neutrons

B) All nitrogen atoms have exactly 7 neutrons.

C) Some nitrogen atoms have more than 7 neutrons.

D) A small percentage of nitrogen atoms have fewer than 7 neutrons.

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• Dr W
Lv 7
1 month ago

C is the correct choice.

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let's start here

.. mass proton = 1.0073 amu

.. mass neutron = 1.0087 amu

.. mass electron = 0.00055 amu

next..

atomic mass = mass protons + mass neutrons + mass electrons - mass defect

we can easily sum up the masses of protons + neutrons + electrons (in a neutral atom)... but.... we don't know mass defect

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So, the best way to solve this is to lookup the isotopic mass of N-14 https://en.wikipedia.org/wiki/Isotopes_of_nitrogen

.. isotopic mass N-14 = 14.003 amu

since the relative atomic mass = 14.01 that means some atoms of N will have more than 7 neutrons to increase the weighted average above 14.003

now let's consider this example.  let's say we have 60% N-15 atoms and enough N-7 to N-12 atoms to bring the weighted average down to from 15.003 to 14.01.  meaning we can't say from this analysis that there is only a small percentage of N atoms with > 7 neutrons

what we can say is there are at least SOME N atoms with # neutrons > 7

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although both (A) and (C) are correct in reality, there is only choice you can logically assume is correct... (C)

• Anonymous
1 month ago

The answer is B, because there are no known isotopes of nitrogen.

• 1 month ago

none of the above.  it is possible to have both fewer than and more than 7 neutrons in a portion of the population.  The variation from ideal (the "ideal" being 14AMU) is not necessarily due to an excess of neutrons in a small portion of the population either.  Only 12C has exactly 12 AMU (by definition).

• 1 month ago

C) Some nitrogen atoms have more than 7 neutrons.