Why do metal ions dissolve in water?
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Water is a polar molecule.
Due to how the two hydrogen and oxygen share their electrons, the water molecule forms a kind of triangular shape. Think Micky Mouse’s head. The 2 ears are Hydrogen, the head, Oxygen. The oxygen pulls the 2 electrons the Hydrogen has closer towards it. As a result, the ears side (Hydrogen) is slightly more positive with and the head side (Oxygen) is slightly more negative. If something can break down into ions, it will get carried away by either the H side or the O side of water depending on which charge the ion has, positive or negative. If we consider salt, salt breaks into Na+ and Cl- ions. The Na+ ions are attracted to the O side of water while the Cl-ions attracted to the H side of water.
To take this one step further, why does oil not mix with water? Oil is non-polar so there is nothing ion the water that attracts any part of oil so they separate.
And final piece. Why does soap remove oil? Soap is a neat product which successfully combines a polar and non-polar compound together via a strong base. By being both polar and non-polar (one side has charges, another side has none, etc.) the non-polar part of soap can dissolve the non-polar oil and then the polar part of soap allows water to wash it away cleaning you.
Water is STRONGLY polar. Like, one of the most polar substances we know of. As a reminder, when a molecule is polar, it means that one end of the molecule has a partial negative charge (called a dipole) , and the other end has a positive dipole. This is why very strongly polar molecules like water form what we call hydrogen bonds, which are very strong intermolecular bonds. In water, the polarity is so strong that fully charged ions are attracted to these ends (in the case of a positively charged metallic cation, it is attracted to the negative end of the water molecule). Hydrogen bonds are so strong as to be able to form complexes with ions, and these ions only enhance the hydrogen bonding between the solvent molecules by increasing the strength of their dipoles.
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