Water has an unusually high melting point
The melting point of water is 0 degrees Celsius -- much higher than expected for comparable molecules.
Scientific Explanation
Ice melts at 0 degrees Celsius — a fact so familiar that it seems perfectly normal. But compared to molecules of similar size and structure, water’s melting point is remarkably high. The closest relatives of water in Group 16 of the periodic table — hydrogen sulfide (H2S), hydrogen selenide (H2Se), and hydrogen telluride (H2Te) — all melt far below minus 40 degrees Celsius.
The reason for this dramatic difference lies in hydrogen bonds. Each water molecule can form up to four hydrogen bonds with its neighbors: two through its hydrogen atoms and two through the lone electron pairs on oxygen. This creates a strong three-dimensional network that holds the molecules together much more tightly than the weak van der Waals forces that dominate in H2S and the heavier hydrides.
To melt ice, you must partially break apart this hydrogen bond network — and that requires significantly more energy. This is why water’s melting point falls within our everyday temperature range instead of somewhere around minus 90 degrees Celsius, as the molecular weight alone would predict.
Step by Step
Group 16 Hydrides
We compare the four Group 16 hydrides: water (H2O), hydrogen sulfide (H2S), hydrogen selenide (H2Se), and hydrogen telluride (H2Te). They are chemically related but differ greatly in molecular weight.
The Expected Trend
For normal molecules, heavier means a higher melting point. From H2Te through H2Se to H2S, the melting point drops steadily. This trend should continue for H2O.
Water's Actual Position
Based on the trend, H2O should melt around minus 100 degrees Celsius. In reality, its melting point is 0 degrees Celsius -- roughly 100 degrees higher than expected. A dramatic jump.
Hydrogen Bonds
The reason: water molecules form a strong network of hydrogen bonds. Breaking this network requires far more energy than overcoming the weak van der Waals forces in the heavier hydrides.
Everyday Relevance
This high melting point has profound consequences for our daily lives and the entire planet. If water were a “normal” molecule, its melting point would be around minus 90 degrees Celsius — far below the temperatures found on Earth’s surface. There would be no ice, no glaciers, no snow. Rivers and lakes would never freeze over.
It is precisely because the melting point sits at 0 degrees Celsius that we experience the constant interplay between ice and liquid water: snowfall in winter, ice cubes in drinks, frost on windshields. This phase transition at an accessible temperature makes water the only substance we routinely encounter in all three states of matter in everyday life.