Fix the formula for Mg3F
Write out the full correct formula?

Explanation:

Hello!

In this case, since, when we see an ionic binary salt like that formed by magnesium (metal) and fluorine (nonmetal), in order to set up the correct molecular formula we need to check out the periodic table in order to identify the suitable oxidation states, since metals remain positively charged as they lose electrons and nonmetals negatively charged as they gain electrons.

In such a way, since the oxidation state of magnesium is +2 and that of fluorine is -1 we write:

Next, we need to exchange the oxidation states as subscripts without the charge to obtain:

Which is the corrected molecular formula for magnesium fluoride.

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alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.