A nuclide has 20 electrons and a positive charge. There are 18 neutrons. What is the nuclide?

1 Answer
Sep 7, 2017

Well the mass number is #"39 amu"#, and we can even quote the element as scandium....


We gots an ion with 20 electrons, with a POSITIVE charge. There are thus 21 nucular protons, i.e. #Z=21# (because the neutral element would have 21 electrons). And if #Z=21# then clearly a glance at the Periodic Table tells us that we got the element scandium..... And since this nucleus has 18 neutrons we got #""^(39)Sc#, which is an exceptionally rare scandium isotope, and is likely (momentarily) observed in nuclear reactions of calcium.