Nursing Entrance Exam

chemical composition remain unchanged over time. Chemicals present in biological systems are invariably not at equilibrium; they are far from equilibrium. 9.2.7 Properties of Substances States of Matter Matter on Earth can exist in three main states or phases: solid, liquid, and gas. There is also a fourth phase, plasma, which occurs when matter is superheated. The primary difference between the phases of matter is the behavior of molecules relative to the temperature to which they are exposed. For example, the lower the temperature, the molecules become closer and locked together; the higher the temperature, the molecules are farther apart the molecules and move relative to one another. Solid Solidmatter exists in a state where its molecules are locked together in a rigid structure that prevents them from moving and, as a result, solid matter is held together in a specific shape. There are two primary types of solids, each defined by the structures in which their molecules are held. When the molecules in solidmatter maintain a uniformorganization, they form a polycrystalline structure. This is howmolecules in metal, ice, and salt are organized. Polycrystalline structures are generally a result of the molecules’ ionic properties. Water molecules, for instance, are formed in such a way that there are distinct ends – one with two hydrogen atoms and one with a single oxygen atom. The structure of the atoms within a water molecule means these ends are charged, giving it poles and causing water molecules to join only in specific patterns. Under a microscope, polycrystalline solids are described as resembling lattice work or a chain link fence, with the same pattern of molecules from one end to the other. When molecule’s electromagnetic properties do not incline them to form into particular structures, they glob together in any patterns possible. This produces amorphous solids, most notably foams, glass, and many types of plastic. Amorphous solids have no regular pattern throughout their structure and, as a result, are poor conductors of heat and electricity. Liquid When solids are heated past a certain point, the electromagnetic bonds holding their molecules together loosen, and the molecules are able to move more freely. While the temperatures required for this to happen can vary widely, the physical qualities of liquids always remain constant. Liquids are considered to be fluids, which differ from solids primarily in their ability to take the shape of any container inwhich they are held. This is the result of a less intense electromagnetic connection between the molecules than there is in solids; however, there is still enough of that liquid that wants to stay all in the same place. This is why liquids still maintain a low density that is nearly identical to their densities in solid form. It is also why liquids will maintain a constant volume rather than just drift off the way gasses do.

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