When you heat water on a stove, something dramatic happens at 100°C: bubbles form not just at the surface but throughout the entire liquid, and water rapidly escapes as steam. This is boiling — the point where a liquid gains enough energy for its molecules to overcome intermolecular attractions and fly off as gas in bulk. Below the boiling point, evaporation only happens at the surface; at the boiling point, the liquid transforms into gas from every point within. Critically, boiling point depends on pressure: on top of Mount Everest, where atmospheric pressure is about one-third of sea level, water boils at around 70°C — too cool to properly cook food, which is why mountaineers use pressure cookers.
Boiling points across the periodic table span an enormous range. Helium has the lowest boiling point of any element: -269°C (just 4 degrees above absolute zero), which makes liquid helium invaluable for cooling MRI magnets and particle accelerators. Nitrogen boils at -196°C and is widely used in cryogenics — flash-freezing food, preserving biological samples, and creating dramatic fog effects at concerts. At the other extreme, tungsten boils at a searing 5555°C and rhenium at 5596°C — temperatures found on the surface of some stars. Water's boiling point of 100°C at sea level is remarkably high for such a small molecule, a consequence of strong hydrogen bonding between water molecules.
Boiling point is a practical workhorse in chemistry and industry. Fractional distillation separates crude oil into gasoline, kerosene, diesel, and heavy oils based on their different boiling points — lighter molecules with lower boiling points rise first. Distillation also produces pure water, spirits, and essential oils. Chemical engineers design processes around boiling points to separate mixtures, purify compounds, and control reactions. Even cooking relies on boiling point: deep-frying works because oil's boiling point (~300°C) is far above water's, allowing it to reach temperatures that create the crispy Maillard reaction on food surfaces.