Question

What is the Lewis structure for \[C{{a}^{2+}}\] ?

Answer 1

Hint: We know that to determine the answer we should know what Lewis notation is. Lewis notation is a way to show the valence shell electrons of an atom or the bonded and non-bonded electron pairs of the molecules. Lewis notation represents the electron as a dot around the symbol of the atoms.

Complete step-by-step answer:
We will use the following rules to write the Lewis structure: For an atom: We will write the electronic configuration of the atom to determine the valence electrons. Then we will write the symbol of the atom. Then we will represent each valence electron as a dot around the symbol of the atom.
The rules to write the Lewis notation for molecules is as follows: We write the basic structure. Then decide the central atom around which we write all atoms of the molecule. The least electronegative atom is the central atom. Then we count the total of valence electrons. Two electrons are used in the formation of a bond. Then we count the total electron used in bond formation. We subtract the electrons used in bond formation from the total valence electrons.

The atomic number of calcium is \[20,\] and the atomic number of argon (a noble gas) is \[18\] , so calcium is on the second column of the periodic table. Since we are talking about the $2+$ cation, it already lost two electrons. We can tell because each electron brings a \[1-~\]charge, and so losing a \[1-~\]charge is like gaining a \[1+~\] charge. Also, since neutral \[~Ca~\] is on the second column/group, it originally had \[2\] electrons. \[2-2=0\], so \[C{{a}^{2+~}}\] has no valence electrons .

Therefore, drawing the Lewis structure is actually not too hard; just write \[Ca\], and mention somehow that it has a \[2+~\] charge. One way you could do it is to enclose \[Ca\] in square brackets and put the \[2+~\] up top like so: ${{[Ca]}^{2+}}$.

Note: Remember that the electrons present in the outermost shell are known as valence shell electrons. We show only valence shell electrons in Lewis notation, not the inner shell electrons. According to the octet rule, any atom requires eight electrons to complete an octet but hydrogen requires two electrons to complete its octet. The lone pair electron density lies only on one atom whereas the bond pair electron density lies in between two bonded atoms.