# 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.

### 4 Answers

- Dr WLv 72 months ago
C is the correct choice.

*******

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

*******

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

*******

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

- Anonymous3 months ago
The answer is B, because there are no known isotopes of nitrogen.

- busterwasmycatLv 73 months 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).