Atomic number (number of protons in the nucleus): 19 Atomic symbol (on the Periodic Table of Elements): K (from the Latin word for alkali, kalium .) Atomic weight (average mass of the atom): 39.0983 ...

So, the mass number of this potassium isotope is 39. Atomic Number and Mass Number of First 30 Elements. Students are generally advised to memorise the first 30 elements from the periodic table.

Lithium, for example, with an atomic number of 3, is a reactive metal — just like sodium (element number 11) and potassium (number 19). A good way to think about it is to imagine running your ...

Predictive power. Gallium. Mendeleev left blank spaces in his original periodic table so that he could properly line up the known elements. Gallium, element 31, was his first gap to be filled, in ...