All atoms of a given element contain the same number of protons and the same number of neutrons?

All atoms of a given element contain the same number of PROTONS. The atoms of a given element may contain DIFFERENT number of neutrons.

The number of PROTONS, massive, positively charged nuclear particles, gives ##Z##, the , and determines the identity of the element. The nucleus MAY contain various numbers of NEUTRONS, massive, neutral particles, and this gives rise to the existence of , atoms of the SAME element but with different mass. See this