The number at the lower left of each element symbol in the above reaction is the proton number.
atomic number n.
Abbr. at. no., at no
The number of protons in an atomic nucleus; it indicates the position of an element in the periodic table.
|atomic number |
The number of protons in the nucleus of an atom. In electrically neutral atoms, this number is also equal to the number of electrons orbiting about the atom's nucleus. The atomic number of an element determines its position in the Periodic Table, and is usually denoted by the letter Z and written as a subscript before an element's symbol, as in 92U.