Why are soapy molecules so attracted to calcium and magnesium ions?

Soapy molecules, or surfactants, have hydrophobic (water-repelling) tails and hydrophilic (water-attracting) heads. Calcium and magnesium ions are positively charged and can interact with the negatively charged head groups of surfactants. This interaction stabilizes the surfactant molecules in solution, reducing the surface tension of water and enabling the formation of micelles, which enhances their ability to emulsify and remove dirt and grease. The presence of these divalent ions can also lead to the formation of insoluble precipitates, which can reduce the effectiveness of some soaps.