Mg (2.8.2) + 2Cl (2.8.7) ==> Mg²⁺ (2.8) 2Cl^– (2.8.8)

can be summarised electronically as [2,8,2] + 2[2,8,7] ==> [2,8]²⁺ [2,8,8]^–₂  via electron transfer

so both the magnesium and chloride ions have a full outer shell of electrons like a noble gas

ONE atom combines withTWO atoms

to form

Note in this electron diagram, only the original outer electrons are shown above.

NOTE

You can draw two separate chloride ions, but in these examples square brackets and a number subscript have been used, as in ordinary chemical formula.

The valency of Mg is 2 and chlorine 1, i.e. the numerical charges of the ions.

Beryllium fluoride BeF₂, magnesium bromide MgBr₂, calcium chloride CaCl₂ or barium iodide BaI₂ etc. will all be electronically similar.

represents the full electronic structure diagram of the magnesium ion [2.8] and the chloride ion [2.8.8], hence the full electronic structure of magnesium chloride.

Note that the 'blob' and 'x' electrons are identical, but their use is just a useful visual device to show how the ion is formed. The blue circle represents the nucleus.

The electronic dot & cross for the ionic bonding in the ionic compound magnesium chloride

is the simplified Lewis dot and cross diagram for the formation of magnesium chloride

Melting point of magnesium chloride is 714^oC

(see extra comments after calcium chloride diagrams)

Ca is 2.8.8.2, Cl is 2.8.7, F is 2.7 rest of dot and cross diagrams are up to you, but calcium chloride is shown below.

The calcium atoms transfer their two outer electrons to the outer shell of two chlorine atoms

calcium chloride

The two outer electrons of the calcium atoms (2.8.8.2) are transferred to the outer shell of two chlorine atoms (2.8.7) until it has a complete octet shell of outer electrons, just like a noble gas (2.8.8).

At the same time, the calcium ion also attains a stable noble gas electron structure (2.8.8). The blue circle represents the nucleus.

is the Lewis diagram for the formation of calcium chloride

Extra comments on magnesium chloride and calcium chloride

Melting point of calcium chloride is 772^oC and magnesium chloride is 714^oC - very high and expected for a giant ionic lattice of a typical ionic compound with a strongly bonded 3D crystal lattice of alternating positive (calcium/magnesium) and negative ions (chloride) that strongly attract each other.