Draw the Lewis dot structure for Mg and S. Is it an ionic or covalent bond?

The Lewis dot structure for MgS (Magnesium sulfide) is difficult to draw in this format.

Iprefer to use a small circle for the metals and a dot for the nonmetal.  This way you can 'see'(distinguish) each atoms electrons

Start by writing the symbol Mg and place a small circle at each the upper right and lower right sides(2 and 4 o'clock).  Then to the right of Mg (give yourself a little space) write the symbol S. Starting at 2 o'clock place a dot,  then place one at 4, 8, and 10 o'clock, respectively).  You have now accounted for 4 of sulfurs 6 valence electrons.  Now place a dot next to the ones at 2 and 4 o'clock.

o----.     :

Mg        S

o----.     :

The dashed line represents the bonding electron pairs.

Now for the QUESTION - is this an ionic bond.

First check the electronegativity(the desire to give up or take electrons) for each element.  Magnesium (Mg) has an electronegativity of 1.29 and sulfur's is 2.46.  Take the difference in electronegativity (2.46-1.29) 1.17.  This then will tell you the type bond (covalent - sharing) (polar-covalent - uneven sharing) or (ionic -little to no sharing of electrons).  It is generally accepted that if the difference in elecrtonegativities is GREATER than 1.7 the bond is ionic (>50% ionic).  Between 0.7 and 1.7 polar covalent (eg. water H2O ~1.1) and less than 0.7 covalent (eg. Nickel(II)sulfide NiS ~0.6,   H2 difference = 0 PURE covalent bond)

Thus NO compound is purely ionic.

Difference in electornegativity

0-----------0.7---------------------------1.7---------------------4.0

covalent---------polar covalent----------------  ionic------  XXX

Hope this helped clear up covalent vs ionic bonds a little.