Q7.What are electrons shells?
Electrons behave as if they are stacked around the nucleus at different levels, like the layers of an onion. These levels are called shells, and there is room for only a particular number of electrons in each shell. The number of electrons in the outer shell determines how the atom will react with other atoms. An atom with a full outer shell, like the gas argon, is unresponsive. An atom with room for one or more extra electrons in its outer shell, like oxygen, is very reactive.