If a neutral atom has 12 electrons, how many can be used for creating bonds?

1 Answer
Jul 13, 2016

Since a neutral atom was requested, its charges must cancel, and therefore, its atomic number must have been 12.

The neutral atom "Mg" has atomic number Z = 12, and it indeed has 12 electrons:

  • two 1s electrons
  • two 2s electrons
  • six 2p electrons
  • two 3s electrons

Since "Mg" is on group 2, it has two valence electrons that it can donate to form the "Mg"^(2+) ion at most (before it becomes energetically unfavorable to donate more, as it is now noble-gas-like).

These donated valence electrons go into making bonds.

A suitable atom, such as---but not limited to---"Cl" (from group 17), can accept "Mg"'s electrons.

Since each "Cl" needs one valence electron, two "Cl" atoms can each accept one valence electron to account for "Mg"'s two 3s valence electrons.

Hence, a compound containing "Mg" and "Cl" would be \mathbf("MgCl"_2), magnesium chloride, where "Mg" makes two single bonds by donating its two total valence electrons in conjunction with one valence electron from each "Cl":

stackrel(..)"Cl"-"Mg"-stackrel(..)"Cl":
""^(..) color(white)(iiiiiiiiiiiii)""^(..)