Question

An ion with mass number 37 possesses one unit of negative charge. If the ion contains 11.1% more neutrons than electrons, then find the symbol of ion.

Answer 1

Hint: To find the symbol of ion we need its atomic number. Atomic number means number of protons. So in this question we actually have to find out the number of protons in the nucleus of the atom from which this ion has formed. Mass is the addition of the number of protons and the number of neutrons.

Complete answer:
 Mass number = number of protons + number of neutrons
Suppose number of protons are A and number of neutrons are N
Mass number = A+N
As mass number given is 37, therefore
A+N=37…………………………equation(1)
As the number of electrons in an atom is always equal to the number of protons and here we are having an ion that contains -1 negative charge, therefore the number of electrons will be 1 more than the number of protons.
Number of electrons= A+1
As number of neutrons are 11.1% more than number of electrons, so
\[[\dfrac{N-(A+1)}{A+1}]100%=11.1\]
$[N-A-1]100=11.1(A+1)$
$100N-100A-100=11.1A+11.1$
$100N-100A-11.1A=100+11.1$
$100N-111.1A=111.1$…………………………………..equation (2)
Multiply equation (1) by 100 both sides and subtract the equation(2) from it
$100A+100N-[100N-111.1A]=3700-111.1$
$100A+111.1A=3588.9$
$211.1A=3588.9$
$A=\dfrac{3588.9}{211.1}$
$A=17$

It means number of protons in the ion are 17 and 17 is the atomic number of chlorine, that clears that it is a chloride ion whose symbol is $C{{l}^{-}}$

Additional information: Chlorine has 7 electrons in its outermost shell, so it needs one more electron to have an octet like a nearest noble gas, therefore it has the tendency to accept one electron and form univalent negative ions.

Note: A quark is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles. Only two types of quark are necessary to build protons and neutrons, the constituents of atomic nuclei. These are the up quark, with a charge of $+\dfrac{2}{3}e$, and the down quark, which has a charge of $-\dfrac{1}{3}e$ . The proton consists of two up quarks and one down quark, which gives it a total charge of +e. Similarly a neutron is made of 1 up quark and 2 down quark.