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Lewis Structure of Magnesium Fluoride (MgF2)

Magnesium fluoride (MgF2) is not a molecular/covalent compound; magnesium has a low electronegativity (it is a metal, after all) and fluorine has a high electronegativity (it is a non-metal, halogen, and has the highest electronegativity of all atoms on the table). So, a transfer of electrons occurs.

Magnesium, when it bonds to a non-metal, always loses two electron to become a +2 ion. This is because the neutral atom has two valence electrons in its outer shell, and to satisfy the octet rule, it wants to lose those two electrons. This makes it a cation.

Fluorine atoms, on the other hand, carry seven valence electrons in the outer shell of their neutral atoms. So their preference is to gain one electron each, and get a -1 charge; this negatively-charged particle is called an anion.

We require one magnesium atom, giving away its two electrons, giving one electron each to two fluorine atoms:

And you can watch this process occur here:

This ionic structure is similar to MgO, which is also ionic. It is not to be confused with other three-atom compounds, made entirely of non-metals, like SF2, which is a covalent compound.

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Lewis Structure of MgO, Magnesium Oxide

Magnesium oxide is an ionic compound. Its formula unit (MgO) is made from one magnesium atom, which loses two electrons to become a +2 cation, and one oxygen atom, which gains those two electrons to become a -2 anion.

The Lewis Structure can show the transfer of electrons from metal (low electronegativity) to non-metal (high electronegativity). Observe below.

You can watch this getting drawn in the video below.

Magnesium oxide does not hybridize to do this, so if you’re looking for the molecular shape, it does not exist. Remember, ionic compounds are crystal lattices, which means the ions (Mg+2 and O-2) surround each other and hold together with ionic bonds. It crystallizes in a face-centred cubic structure, which has an octahedral coordination geometry – each Mg+2 is surrounded by six O-2 ions, and each O-2 ion is likewise surrounded by six Mg+2 ions.