Chemistry deals with the properties of substances

Some substances around us are solids. Some are harder than others. There are substances that are liquids. Or gases. Some substances easily react with other substances.

While others are stable. Why is this? Why do different substances have different properties? Chemistry is the field of science that tries to answer that very question. And most of the time we have to zoom in extremely close to find the answer.

We need to look at the atoms of the substance. Here are some iron atoms. They are firmly attached to each other - they have formed strong bonds. If we try to move the atoms, the bonds pull them back. Iron is a hard material.

If we heat the iron, the atoms move around more. But they still stay in their places. Iron is a solid material, even at hundreds of degrees Celsius. We need over a thousand degrees for the atoms to start to move out of place - for the iron to melt. Compare that to this substance - carbon atoms and hydrogen atoms in long chains.

The substance we're looking at now is a kind of plastic, like the material of the beach ball. Each chain of atoms - each molecule - is kept together by strong bonds. But the molecules aren't attached to each other as firmly. They can slide against each other. This plastic material can change its shape - it is soft.

At room temperature it is a solid substance, but it's enough to heat it just a little... ... for the molecules to start moving all over the place - the plastic has melted. When the bonds between molecules are weak, the substance will turn into a liquid at a lower temperature. Let's look at a gas as well. This is a mixture of hydrogen and oxygen.

The atoms in both hydrogen and oxygen are attached two by two. The bonds between the atoms are strong in each molecule. Between the molecules, however, the bonds are really weak, almost non-existent The molecules can fly around freely - they are gaseous. One property of hydrogen and oxygen is that they can react easily with each other - they are reactive. When substances react their atoms bond together in new ways.

What makes hydrogen and oxygen reactive is that the atoms would really like to form a new molecule: water. The plastic in the beach ball is also reactive, if heated sufficiently. The atoms form new bonds with the oxygen atoms in the air. Plastic can burn. The atoms in these stones, on the other hand, won't react.

They are happy with the bonds they have already. Why is iron a hard material, and plastic soft? Why do iron and stone have high melting points, and plastic a low melting point? Why are hydrogen and oxygen gases at room temperature, and why are they so reactive? And why does the beach ball, but not the stones, react with the oxygen in the air when it is heated?

All that has to do with how the atoms of the substances are attached to each other. It's the bonds between the atoms, and the strength of those bonds, that affect the properties. And this very thing - the properties of substances, and how they react with each other - that is what chemistry is all about.