# Why does MgCl2 become Mg^2+ and Cl^-? [closed]

I'm taking a biology class, and it's one-chapter intro to chemistry chapter had been driving my study group nuts. On a recent quiz, it asked the question:

In water, $$\ce{MgCl2}$$ dissociates into $$\ce{Mg^{2+}}$$ and $$\ce{Cl-}$$. Based on this information what type of bond is involved in the formation of $$\ce{MgCl2}$$?

I guessed (and got correct) that the bond was ionic, since the only thing that changed in their symbols was the ionization ($$\ce{Mg}$$ has +2 electrons, $$\ce{Cl}$$ is -1 electron). What it doesn't explain (it literally doesn't even attempt to explain), is how do these break apart to form two ions? At first I thought this had to do with the stability of common $$\ce{Mg}$$ and $$\ce{Cl}$$, but since they both are missing electrons in their outermost shell, that didn't seem to be the way to go. So at this point, we're all lost, and the textbook/professor's explanation of another question which made it sound like the periodic table measures atomic mass in grams instead of Da makes us have no confidence in what it's explaining.

## closed as unclear what you're asking by andselisk, Zhe, Mithoron, A.K., Todd MinehardtFeb 2 at 23:52

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Hello and welcome to Chemistry Stack Exchange! You may go through the tour page (chemistry.stackexchange.com/tour) and the help center (chemistry.stackexchange.com/help). While your question is not entirely correct, I believe that there may be a typo mistake in your title ($\ce{Mg}$ instead of $\ce{Na}$). Also, please use mhchem (LaTeX commands for chemistry formatting) to make chemistry terms stand out in your text clearly. – AbhigyanC Feb 2 at 15:26
• The Compound MgCl2 consists of magnesium 2+ ions and Cl- ions already. No electrons are transferred in the process of getting those ions into solution. – matt_black Feb 3 at 14:36

From reading your question, maybe it's best to begin with an introductory chemistry course for even younger students (not to demean you or disrespect you in any way) so that you may learn better. I'd suggest Khan Academy - Atoms, compounds, and ions. This should show you the way through whatever chemistry you need to study biology.

Regarding your question specifically, don't worry too much.

In water, MgCl2 dissociates into $$\ce{Mg^{2+}}$$ and $$\ce{Cl-}$$. Based on this information, what type of bond in involved in the formation of $$\ce{MgCl2}$$?

Think of what the question suggests. It tells us clearly that the substance $$\ce{MgCl2}$$ has dissociated into two ions $$\ce{MgCl2->Mg^{2+} + Cl-}$$. This could happen only if ions were present in the substance to begin with. Hence, the substance must have had ions, which would be held together by ionic bonds.

(Regarding the atomic mass being measured in grams and not Daltons, don't worry. That is irrelevant to this topic, and probably came up due to some other discussion.)

I further repeat my advice, please go through an introductory level chemistry course which will make you comfortable with basic chemistry and the principles which you will need to apply for biology. I speak from experience, having faced a similar condition a couple of years ago...

Water molecules have what is called a dipole. Basically oxygen atoms are more capable of attracting electrons to them than hydrogen atoms(oxygen is more electronegative than hydrogen). This results in the oxygen end of the water molecule having a partial negative charge and the hydrogen end having a partial positive charge. So what happens when you add magnesium chloride to water is that the hydrogen end of water is attracted to the negative chloride ions in the lattice so water molecules surround the chloride ions using their hydrogen end. The opposite occurs for the magnesium ions where now the oxygen end of thewater molecules is attracted to the magnesium ions in the lattice so water molecules surround magnesium ions using their oxygen end. The magnesium ions and chloride ions are now separate and can move freely in water.This is known as hydration.

This pic is of sodium chloride but it's the same as magnesium chloride.

I didn't really get your question but I hope this answers it!