It’s a hot summer day. You’re relaxing by the pool, and you suddenly have the urge for a cool treat. After a quick trip to the snack bar, you sit back to soak up the Sun’s rays with a tall glass of iced tea and an ice cream bar.
Suddenly, a friend across the pool shouts your name. You run over to greet your friend who you haven’t seen since school let out. After catching up for a few minutes, you return to your seat to find a disaster has occurred.
Leaving ice cubes and ice cream in the hot Sun’s rays is not a good idea if you want to keep them cool. Why not? Everyone knows the answer: they melt. But have you ever WONDERed exactly why things melt when they get hot? What exactly is going on here?
Melting is a natural, scientific process that scientists call a phase transition. It occurs on the molecular level. Everything you see around you is made up of molecules. Molecules are tiny particles that you usually can’t see with the naked eye.
Molecules are made up of basic building blocks called elements. A water molecule (H2O), for example, is made up of two elements: hydrogen and oxygen. Specifically, each water molecule contains two hydrogen atoms and one oxygen atom.
When water is in its solid state, which we call ice, its individual molecules are packed tightly together. In fact, they’re packed so tightly that they can barely move. This is what gives ice its solid nature.
When energy is added in the form of heat, the water molecules begin to get excited and move around. As more and more heat is added, the molecules move faster and faster, causing the structure of the molecules to loosen. As the structure loosens, more movement is allowed. You see this in the form of solid ice turning to liquid water, or what we know as melting.
As a liquid, water molecules can still hang together, but they move around easily. If additional heat is added, they will get so excited that they can no longer hold together. When this happens, the liquid turns into a gas and the molecules break apart and escape into the air.
The temperature at which a substance turns to a liquid is called its melting point. Every substance has a melting point. For example, the melting point of water in the form of ice is 32º F. As the temperature rises above the 32º F mark, ice will begin to melt into liquid water.
Many other substances have melting points that are much higher than that of ice. The specific properties of the atoms in a solid and the way in which they bond to each other determine a substance’s melting point.
For example, the chemical elements with the highest melting points are tungsten and carbon, which melt at 6,192º F and over 7,000º F, respectively. Scientists have also been able to mix various metals together to make alloys with extremely high melting points. One such alloy, tantalum hafnium carbide, melts at an astounding 7,619º F!