If an atom has a mass of 11 amu and contains 5 electrons, what is its atomic number?

Question

If an atom has a mass of 11 amu and contains 5 electrons, what is its atomic number?

Answer 1

Boron, element number 5.  The trick part of this question is to figure out whether the atom is neutral; just because it has five electrons doesn't mean that the atomic number is five.  (Singly ionized carbon, for example, has five electrons.)  But only boron has both 5 electrons (in the unionized state) and a mass of 11.

Answer 2

If you look on the periodic table, you can see that the element Boron has an atomic number of 5 and a molar mass of about 11 amu. Since the atomic number represents both the number of protons and electrons in the atom, this atom has an atomic number of 5 since it contains 5 electrons. Although you could have figured that out without the use of the periodic table, it's always good to check as sometimes you may be given isotopes which have a different molar mass but the same atomic number. You may also be given ions which have different numbers of electrons which means different charges.

Answer 3

I would think 5.

But I haven't done anything Chemistry related for ages.