a·tom·ic num·ber
noun/əˌtɒmɪk ˈnʌmbə(r)/
/əˌtɑːmɪk ˈnʌmbər/
(chemistry)- the number of protons in the nucleus (= centre) of an atom of a particular chemical element. Elements are placed in the periodic table according to their atomic numbers.
原子序数（指原子在元素周期表中的序号）