Mercury and water are not the only substances capable of existing in three distinct states of matter. In fact, all of the elements, of which mercury is one, may exist in solid, liquid, or gas forms. Additionally, many substances exhibit more than one solid form, often with very different properties. For example, both graphite and diamond are composed of carbon, but the arrange of carbon atoms within the solid is different.

For simplicity, consider pure substances such as water. The stable form of matter, or phase, of a single component system depends on the temperature and pressure of the system. We are typically used to atmospheric pressure. Therefore, we expect water to be a liquid at room temperature, to freeze to a solid below 32 degrees Fahrenheit (0 deg Celsius), and to boil into the gas phase above 212 deg F (100 deg C). However, if you placed a glass of water inside a vacuum and reduced the pressure to one tenth of the normal atmospheric pressure, the water would boil even in a nicely air conditioned room.

The same is true for other substances, although the temperatures and pressures at which a given phase is stable may be so extreme that for all practical purposes you'll never encounter it. For example, the gas phase of copper is stable at atmospheric pressure only at temperatures above 4643 deg F (2562 deg C); however, if you wanted to obtain the gas phase near room temperature, you would have to reduce the pressure to less than one billionth of atmospheric pressure.

This is not true; in fact all of the elements except for helium go through all three phases of matter (solid, liquid, and gas) as the temperature is varied. That is to say, at low enough temperatures, all the elements (except Helium) are solids. As the temperature is increased they will melt and become liquids. Each element melts at a different temperature, called it's "melting point". Hydrogen melts at -259 degrees Celsius. Mercury melts at -39 degrees Celsius. Iron melts at 1,535 degrees Celsius. As the temperature is increased still further, each element will boil and become a gas. Each element boils at a different temperature, called the "boiling point". For Hydrogen, the boiling point is -253 degrees Celsius; for mercury it is 357 degrees Celsius, and for iron it is 2,750 degrees Celsius.

From these numbers you can see that at room temperature (and indeed for nearly any temperature found on Earth) hydrogen is a gas, mercury is a liquid, and iron is a solid. This discussion also holds true for small molecules, like water (H₂O), carbon dioxide (CO₂), etc. Water is the only substance where all three states can be readily observed in everyday life: solid water as ice, liquid water in a water fountain, and gaseous water as steam. Carbon dioxide is a good example of a substance which can be a liquid, but only when it is under pressure. For example, at room temperature unpressurized carbon dioxide is a gas, but if it is pressurized to 800 pounds per square inch (as it often is in steel bottles), it becomes a liquid.

Helium (an element) is unique in that it will not freeze no matter how cold it is made unless it is simultaneously very cold (colder than -270 degrees C) and under a great deal of pressure (about 400 pounds per square inch). Thus you can see that all the elements and all the simple molecules can be made to go through all three phases if you can control the temperature and the pressure they experience. It might seem that this would mean that any substance could be made to be solid, liquid or gas, but this is not quite true. For example wood, which is made out of very large, complicated molecules containing mostly carbon, hydrogen, oxygen, and nitrogen, does not boil - i.e., when you heat it it does not melt into liquid wood and then boil into gaseous wood. Instead as the wood becomes hot (about 300 degrees Celsius), the big molecules break up into smaller molecules like carbon dioxide. Carbon dioxide is a gas at 300 degrees Celsius, so it floats away. This process is called "burning", and is the result of the big molecules of the solid wood breaking up into small molecules like Carbon Dioxide, which then float away as a gas. If you are interested, there is a table of all the melting and boiling points of all the elements at

This is not true. All substances go through all the phases, but at different temperatures and pressures. Mercury and water are both liquid at room temperature and 1 atmosphere of pressure. You can make water boil, however, by putting it in a vacuum!

Boiling is the process of a substance changing from liquid to gas phase. You can make water do this at room temperature by putting it in a heavy container and removing all the air - putting it in zero air pressure - then the water comes out of liquid phase and changes into gas phase! Substances like hydrogen, methane gas, and carbon dioxide, which are found on earth as gases, are found on the outer planets like Saturn as ices. Substances like iron, silicon, carbon, that are found on earth as solids, are found in the Sun as ionized gases, or plasmas!

What do you mean by phases?. I presume you mean the solid, liquid or gas phases. If so, your statement is not accurate. Most elements can be made into one of these phases. Metals solid at room temperature can be made into liquids by heating and even into gases by heating the liquid to high temperature. Even helium which is a very cold liquid in its usual state at atmospheric pressure can be made into a solid by compressing the liquid or into a gas by heating the liquid.

I hope this is clear for you now.

Almost all substances have a solid, liquid, and gas state. I think mercury is interesting because (as stated in the CRC Handbook of Chemistry and Physics) it is the only common metal that is a liquid at room temperature and atmospheric pressure. Water is also very interesting, and makes life as we know it possible, because it is a liquid at room temperature and at one atmosphere.