Magnesium has an atomic number of 12, so there are 12 protons in any atom of this element. The number of protons do not change if it is an isotope of an element.
20 electrons
42 electrons
Two electrons from each element are shared; the total is four electrons.
A phosphorus atom has 15 electrons.
6 valence electrons
8 electrons
16 electrons
20 electrons
6 electrons
97 electrons
4 electrons.
4 electrons, 2 valence electrons
Germanium has 32 electrons.
Xenon has 54 electrons.
Argon has 18 electrons.
15 total electrons, 3 valence electrons
Roentgenium has 111 electrons.