The Three States of Matter (Solid, Liquid, Gas) Explained Simply
Almost every substance can exist in three different forms: solid, liquid, or gas. Which form it takes depends mostly on temperature - and the exact temperature where it switches is completely different from substance to substance. Water already turns solid at 0°C, while iron doesn't turn solid until you drop below over 1500°C. Let's take a close look at why.
The more energy (heat) the particles get, the more strongly they move - from the ordered lattice, through the mobile liquid, to the freely flying gas.
In the solid state, particles (atoms, ions, or molecules) sit fixed in place in an ordered lattice. They can't travel through the substance, only vibrate on the spot - which is why a solid object keeps its shape and volume on its own.
In the liquid state, particles are packed almost as tightly as in the solid state, but they can slide past one another. That's why a liquid takes the shape of its container while keeping its volume - you can't noticeably compress water.
In the gas state, particles barely touch each other at all. They fly through space quickly and randomly, spreading out evenly until they hit a wall. That's why a gas always fills the entire available space and can easily be compressed.
The switch between states doesn't happen at just any temperature - it happens at a point that's exactly fixed for each substance: the melting point (solid → liquid) and the boiling point (liquid → gas), both measured at standard pressure (1013 hPa, roughly the air pressure at sea level). And these points differ dramatically from substance to substance:
The bar shows each substance's liquid range - to the left of the bar it's solid, to the right it's gas. Water has the smallest liquid range at just 100 degrees, iron the largest.
💬 Mia asks Grandpa Theo
Why does water already turn solid at 0°C, but iron not until above 1500°C?
It depends on how strongly the particles are held together. In metals like iron, very strong metallic bonds hold the atoms together - breaking those takes an enormous amount of energy, meaning high temperature. Water molecules, on the other hand, are only held together by comparatively weak hydrogen bonds, which break apart with much less energy.
Why are gold's and silver's melting and boiling points so close together, but still not exactly the same?
Gold and silver atoms are chemically very similar - both are noble metals with similarly strong metallic bonds. But gold atoms are a bit heavier and their bonds are minimally stronger, so gold's melting point - and especially its boiling point - sits a little higher than silver's.
Does water actually boil at exactly 100°C everywhere in the world?
Only at standard pressure at sea level! The lower the air pressure, the more easily water particles can escape - so water boils at a lower temperature high up a mountain. On a 5,000-meter peak, for example, water already boils at around 83°C.
What about glass? When does that turn solid or liquid?
That's exactly what makes glass complicated - unlike water, iron, gold, and silver, glass doesn't have a fixed melting point at all. Let me explain that in more detail.
Water, iron, gold, and silver are crystalline substances - their particles arrange into an exact, repeating lattice in the solid state, which is exactly why there's a precise point where that lattice breaks down. Glass, on the other hand, is amorphous: even in its solid state, its particles stay in a disordered arrangement, almost like a frozen liquid. That's why there's no sharp melting point, only a gradual transition range (called the glass transition range) in which glass just keeps getting softer. For ordinary window glass, this range starts at around 550-600°C, and it only becomes properly flowable and workable at around 1400-1600°C. This is exactly the soft transition that glassblowers rely on to shape glass, since it never suddenly flips from solid to fully liquid.
Whether a substance is solid, liquid, or gas at room temperature isn't random - it comes down to how strongly its particles are held together, and that's exactly what makes water, metals, and glass behave so differently in everyday life.
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