# How many protons and electrons are in an atom of atomic number is 11?

There are $\text{11 protons}$ and $\text{11 electrons}$ in the neutral atom.
The atomic number, $Z$, specifies the number of massive, positively charged particles present in the element's nucleus, and this number defines the identity of the element: $Z = 1$, hydrogen, $Z = 2$, helium, ...... $Z = 6$, carbon........$Z = 31$, gallium, etc.
Because elements, (and all matter) are usually neutral entities, if there are $Z$ positive charges, there must be $Z$ negative charges in the neutral atom. In other words, $Z = \text{number of electrons}$ for the neutral element.
If $Z = 11$, then what is the element? This element has an atomic mass of $23 \cdot \text{amu}$. How do we account for the mass excess to that of the protons? Certainly electrons don't contribute any mass.