Why are Neutrons necessary for a stable nucleus? Predict what would happen to the atom if there were no neutrons? (hint: think of the only element that has atoms with no neutrons)

Very interesting question indeed! I can try to explain this in following words

Explanation:

Neutrons stabilize the nucleus, because they attract each other and protons , which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus.

Secondly if there is no neutrons then the electromagnetic repulsion between proton will not allow any stable nucleus . Also remember in hydrogen there  is only one proton so the repulsion is not experienced hence no need of neutron.

Hope this help!!

explanation:

metals have excess of electrons whereas non-metals have deficiency of electrons. thus, in order to gain stability metals easily donate their electrons to the non-metals.

for example, electronic configuration of sodium is and electronic configuration of phosphorous is .

when a phosphorous atom and sodium atom combine together then sodium will donate is extra one electron to the phosphorous atom. as a result there will be formation of ionic bond between sodium and phosphorous.

the reaction will be as follows.

there, are three sodium sodium atoms and each of them will donate its one extra electron to phosphorous atom. thus, the sub-shell of phosphorous gets completely filled.  

thus, we can conclude that electrons are transferred from atoms of sodium to atoms of phosphorous. this transfer makes the sodium atoms donate one electron and the phosphorous atoms to gain one electron. as a result, the sodium and phosphorus atoms strongly attract each other.