Ionic or Molecular in Everyday Life
In the kitchen there are two white solids that look a lot alike: table salt and sugar. Both dissolve in water, but if you heat sugar in a saucepan it melts and turns into caramel, while salt doesn't budge on the stove. What do they have inside that makes them so different? By the end of this page you'll be able to explain it.
First criterion: look at the formula
You already know that an ionic compound forms when a metal gives up electrons and a nonmetal gains them, and that a molecular compound forms when nonmetals share electrons. That gives us a quick rule for classifying any substance just by reading its formula.
To apply it, you need to locate the elements on the periodic table. Metals are on the left (groups 1 and 2, and most of the center). Nonmetals (H, C, N, O, F, Cl, S…) are on the right, and hydrogen, although it sits at the top left, behaves like a nonmetal.
Classify these everyday substances as ionic compounds or molecular compounds, and note the criterion you used (presence of a metal and a nonmetal, or only nonmetals):…
Classify these everyday substances as ionic compounds or molecular compounds, and note the criterion you used (presence of a metal and a nonmetal, or only nonmetals): table salt (NaCl), water (H₂O), sugar (C₁₂H₂₂O₁₁), baking soda (NaHCO₃), carbon dioxide (CO₂), and quicklime (CaO).
Second criterion: properties
Sometimes you don't have the formula, only the results of an experiment. Then the properties tell you what kind of particles are inside.
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Ionic compounds form a network of oppositely charged ions that attract each other very strongly. That's why they have high melting points and are hard but brittle solids: if you hit a salt crystal, it breaks because when one layer of ions shifts, like charges end up close together and repel each other. Since ions can only move when they are free, they conduct electricity when molten or dissolved, but not as solids.
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Molecular compounds are made of neutral molecules with weak attractions between them. That's why they melt at low temperatures, are usually soft (like wax or sugar, which crumbles easily) or are liquids or gases at room temperature, and do not conduct current in any state, because there are no charges that can move.
| Property | Ionic | Molecular |
|---|---|---|
| Melting point | High (hundreds of °C) | Low |
| Hardness | Hard and brittle | Soft (or liquid or gas) |
| Conductivity as a solid | No | No |
| Conductivity when molten | Yes | No |
| Conductivity dissolved in water | Yes | Usually no |
| Solubility in water | Many are soluble, others are not | Some are (sugar), others are not (oil) |
| Particles | Ions in a network | Molecules |
Two white substances are analyzed in the laboratory. Substance A melts at $160\,{}^{\circ}C$ and conducts electric current neither as a solid nor when molten. Substance…
Two white substances are analyzed in the laboratory. Substance A melts at $160\,{}^{\circ}C$ and conducts electric current neither as a solid nor when molten. Substance B does not melt even over the burner flame, but when dissolved in water it does conduct current. Decide which one is ionic and which one is molecular, and justify your decision with the properties of each type of compound.
Salt and sugar: the kitchen mystery
Let's go back to the caramel on the flan. Sugar is a molecular compound (only C, H, and O). Its molecules attract each other weakly, so with the heat of the stove (about 160 °C) they separate enough and the sugar melts.
Table salt is an ionic compound (Na⁺ and Cl⁻). Each ion is held by the attraction of several neighbors with the opposite charge, and it takes about 800 °C to release them. Although the flame of a gas stove is hotter than that, the bottom of the saucepan only reaches about 200–250 °C, far below the 801 °C that salt needs to melt. That's why salt never melts in the kitchen. That same strong attraction makes salt crystals hard, while sugar cubes crumble easily.
And both dissolve in water: sugar disperses as molecules, and salt as ions. That's why salt water conducts electricity and sugar water does not.
In the kitchen, sugar melts easily when heated (that is how the caramel for flan is made), but table salt never melts on the stove. Both are white solids that dissolve…
In the kitchen, sugar melts easily when heated (that is how the caramel for flan is made), but table salt never melts on the stove. Both are white solids that dissolve in water. Explain this difference in behavior based on the type of bond and the particles each substance forms.
Uses in the body and in daily life
The properties of each type of compound are used in everyday life:
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Ionic: the electrolytes in oral rehydration solution and sports drinks (Na⁺, K⁺, Cl⁻) allow nerves and muscles to transmit electrical signals. Lime (CaO) is used in the nixtamalization of corn. Baking soda (NaHCO₃) serves as an antacid.
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Molecular: water is the solvent of life; sugar and lipids give us energy; the CO₂ in sodas gives them their bubbles.