Gases represent a state of matter that has no fixed shape or fixed volume, which consist of tiny, energetic particles, i.e., atoms or molecules, that are widely spaced. introduction to gases
Gas atoms or molecules are constantly moving and colliding with one another.
Compared to the other states of matter, solids and liquids, gases have a much lower density, i.e., they have a small mass per unit volume, because there is a great deal of empty space between gas particles. At room temperature and pressure, the gas inside a container occupies only 0.1% of the total container volume. The other 99.9% of the total volume is empty space (whereas in liquids and solids, about 70% of the volume is occupied by particles). Gas particles move very fast and collide with one another, causing them to diffuse, or spread out, until they are evenly distributed throughout the volume of their container. You will never see only half of a balloon filled with air.
Although both liquids and gases take the shape of their containers, gases differ from liquids in that there is so much space between gas molecules that they offer little resistance to motion and can be compressed to smaller and smaller volumes.
Oxygen, nitrogen, and carbon monoxide are examples of diatomic molecules. Carbon dioxide, water, nitrogen monoxide, methane, sulfur dioxide, and ozone are examples of polyatomic molecules.
Gases can be monatomic, diatomic, and polyatomic. Monatomic gases are gases composed of single atoms, diatomic gases are those composed of two atom molecules, and polyatomic gases are those made up of molecules with more than two atoms. Noble gases such as helium, neon, argon, etc., are normally found as single atoms, since they are chemically inert. Gases such as nitrogen (N2), oxygen (O2), and carbon monoxide (CO) tend to be found as diatomic molecules. Carbon dioxide (CO2), and methane (CH4) are examples of polyatomic gas molecules.
Gases can be found all around us. In fact, the earth’s atmosphere is a blanket of gases composed of nitrogen (78%), oxygen (21%), argon (1%), and then trace amounts of carbon dioxide, neon, helium, methane, krypton, hydrogen, nitrous oxide, xenon, ozone, iodine, carbon monoxide, and ammonia. Because of the large distances between gas particles, the attractions or repulsions among them are weak. The particles in a gas are in rapid and continuous motion.
Ideal Gases: Scientists often simplify the model of gases by imagining the behavior of an ideal gas. An ideal gas differs from a real gas in that the particles are assumed to be point masses, that is, particles that have a mass but occupy no volume. It is also assumed that there are no attractive or repulsive forces at all between the particles. When all these assumptions are incorporated into a gas model, the “ideal gas model” is obtained. As the name implies, the ideal gas model describes an “ideal” of gas behavior that is only approximated by reality. Nevertheless, the model has been proven to reasonably explain and predict the behavior of typical gases under typical conditions.
Note: Under ordinary conditions, the properties of gases predicted by the ideal gas law are within 5% of their actual values. introduction to gases introduction to gases
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