Question

how do you tell how many electrons there are on the outer level of an atom of an element

Answer 1

you mean from first principles? or like using orbitals

Answer 2

the original question is :

54. To determine the molar mass of an element, one must know the element's __________

Answer 3

amount of neutrons and protons

Answer 4

For the main-group elements, find the column of the Periodic Table in which the element lies, excluding the transition metals.

For example, H, Li, Na, K et cetera lie in the first column, so they have 1 valence electron. Be, Mg, Ca et cetera like in the second column, so they have 2. B, Al, Ga et cetera are in the third column NOT COUNTING THE TRANSITION METALS, so they have 3. C, Si, Ge and so on are in the fourth column, so they have 4 valence electrons. And so on.

The Periodic Table is your friend. You can use it to deduce almost anything about the electron configuration of atoms.