If an atom contains 11 protons and 12 neutrons, what is its atomic number? Chemistry Matter Atomic Number 1 Answer anor277 Sep 7, 2016 #Z," the atomic number"# #=# #11.# Explanation: #Z# is specified by the number of nuclear protons; i.e. the number of positively charged nuclear particles. #Z# specifies the identity of the nucleus. If #Z=11#, then the element is sodium. We would thus describe this species as #""^23Na#. Answer link Related questions How can the atomic number be determined? How can the atomic mass of an element be calculated? How do atomic numbers change in the periodic table? What is the atomic mass in hydrogen? What does the atomic number tell us? Why is the atomic number used to identify elements? Why is the atomic number a whole number? Why is atomic number represented by Z? How did Dmitri Mendeleev contribute to the atomic number? How is the atomic number affected by gamma decay? See all questions in Atomic Number Impact of this question 18915 views around the world You can reuse this answer Creative Commons License