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See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. Stone, iron, pots, pans, plates, sugar, salt, and coffee beans all dissolve in water. Things which dissolve are called solutes and the liquid in which they dissolve is called a solvent. The water molecules surround the charged solute; positive hydrogens close to negative charges and negative oxygens close to positive charges on the solute molecule.
All this interaction suspends the solute molecule in a sea of water molecules; it disperses and dissolves easily. Electrons in the bonds between identical atoms H-H are shared uniformly, so the electrons spend equal amounts of time around each atomic center. These covalent bonds are non-polar. Electrons shared between unlike atoms are not shared equally, one atom gets more of the common electrons and is thus slightly negatively charged.
The other atoms gets less than a full share of the electrons and is thus slightly positively charged. Substances which dissolve easily and readily in water sugar, salt, etc. On the other hand, some solutes are non-polar and do not have any positive or negative charges. Water molecules are not attracted to these types of molecules and, in fact, are sometimes repelled by them. Thus, the exact number of hydrogen bonds formed per molecule varies. Molecules of pure substances are attracted to themselves.
This sticking together of like substances is called cohesion. Depending on how attracted molecules of the same substance are to one another, the substance will be more or less cohesive. Hydrogen bonds cause water to be exceptionally attracted to each other. Therefore, water is very cohesive. Our experience with water, however usually involves water touching something else or being acted upon by gravity. In space, water is able to form perfectly round spheres because the attraction of water to itself pulls the water into the shape with the least amount of surface area compared to the volume — a sphere.
A European Space Agency astronaut Pedro Duque of Spain watches a water bubble float between him and the camera, showing his image refracted, on the International Space Station. B A large water sphere made on a 5 cm diameter wire loop by U. Weird Science. Adhesion is similar to cohesion, but it involves unlike i. Water is very adhesive ; it sticks well to a variety of different substances. Water sticks to other things for the same reason it sticks to itself — because it is polar so it is attracted to substances that have charges.
Water adheres to many things— it sticks to plants, it sticks to dishes, and it sticks to your eyebrows when you sweat. In each of these cases water adheres to or wets something because of adhesion. This is why your hair stays wet after you shower. Molecules of water are actually sticking to your hair Fig. Adhesion also explains why soil is able to hold water and form mud. When the temperature of water decreases, the hydrogen bonds are formed and release a considerable amount of energy.
Water has the highest specific heat capacity of any liquid. Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius.
For water, this amount is one calorie, or 4. As a result, it takes water a long time to heat and a long time to cool. In fact, the specific heat capacity of water is about five times more than that of sand. This explains why the land cools faster than the sea. The resistance to sudden temperature changes makes water an excellent habitat, allowing organisms to survive without experiencing wide temperature fluctuation.
Furthermore, because many organisms are mainly composed of water, the property of high heat capacity allows highly regulated internal body temperatures. For example, the temperature of your body does not drastically drop to the same temperature as the outside temperature while you are skiing or playing in the snow.
Evaporation of water requires a substantial amount of energy due to the high heat of vaporization of water. As a result of the network of hydrogen bonding present between water molecules, a high input of energy is required to transform one gram of liquid water into water vapor, an energy requirement called the heat of vaporization. Water has a heat of vaporization value of A considerable amount of heat energy calories is required to accomplish this change in water.
This process occurs on the surface of water. As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other, which is required for it to enter its gaseous phase steam. Humidity, Evaporation, and Boiling : a Because of the distribution of speeds and kinetic energies, some water molecules can break away to the vapor phase even at temperatures below the ordinary boiling point.
This vapor density and the partial pressure it creates are the saturation values. They increase with temperature and are independent of the presence of other gases, such as air. They depend only on the vapor pressure of water. The fact that hydrogen bonds need to be broken for water to evaporate means that a substantial amount of energy is used in the process. As the water evaporates, energy is taken up by the process, cooling the environment where the evaporation is taking place.
In many living organisms, including humans, the evaporation of sweat, which is 90 percent water, allows the organism to cool so that homeostasis of body temperature can be maintained. Water, which not only dissolves many compounds but also dissolves more substances than any other liquid, is considered the universal solvent.
A polar molecule with partially-positive and negative charges, it readily dissolves ions and polar molecules.
Water is therefore referred to as a solvent: a substance capable of dissolving other polar molecules and ionic compounds. The charges associated with these molecules form hydrogen bonds with water, surrounding the particle with water molecules. This is referred to as a sphere of hydration, or a hydration shell, and serves to keep the particles separated or dispersed in the water. When ionic compounds are added to water, individual ions interact with the polar regions of the water molecules during the dissociation process, disrupting their ionic bonds.
Dissociation occurs when atoms or groups of atoms break off from molecules and form ions. Dissociation of NaCl in water : When table salt NaCl is mixed in water, spheres of hydration form around the ions. Since many biomolecules are either polar or charged, water readily dissolves these hydrophilic compounds. Water is a poor solvent, however, for hydrophobic molecules such as lipids.
Nonpolar molecules experience hydrophobic interactions in water: the water changes its hydrogen bonding patterns around the hydrophobic molecules to produce a cage-like structure called a clathrate.
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