Water is basically a simple molecule, consisting of just two hydrogen atoms attached to a single oxygen atom. Water is transparent, nearly colorless containing a hint of blue, odorless, tasteless and extremely useful as we drink it, wash ourselves and our clothes with it, we cook with it, we swim in it and go boating and fishing on it. This extraordinary substance and yet extremely vital resource is ubiquitous and it has shaped our history and human society. Violent storms and floods can bring water in ferocious abundance causing floods that result in death and disease, and just as quickly drought and desertification can create crippling shortages that cause famine.
When water changes from a gas to liquid this is called condensation. Evaporation occurs when a liquid object changes into a gas far below its boiling point. There are always some particles in a liquid that have enough energy to break free from the rest to become a gas. When ice is heated, it turns from its solid state into a liquid and when water is heated to its boiling point, water will turn into gas which is called steam. Water, unlike any other solid-liquid, is denser in its liquid form than as a solid, which is why ice floats.
The properties of water make it suitable for organisms to survive in during differing weather conditions. Ice freezes as it expands, which explains why ice is able to float on liquid water. During the winter when lakes begin to freeze, the surface of the water freezes and then moves down toward deeper water, thus allowing people to ice skate on or fall through a frozen lake. If ice was not able to float, the lake would freeze from the bottom up killing all ecosystems living in the lake. Since ice floats, the fish are able to survive under the surface of the ice during the winter. The surface of ice above a lake also shields lakes from the cold temperature outside and insulates the water beneath it, allowing the lake under the frozen ice to stay liquid and maintain a temperature adequate for the ecosystems living in the lake to survive.
Many people feel that water is just plain boring, because when you look at water, it is virtually colorless and it has no taste or smell, but this is far from the truth, as water is an extremely exciting substance. Water consists of two much lighter hydrogen (H) atoms and one heavier atom of oxygen (O) and it has the chemical formula H2O. This formula does not convey the shape of the molecule, and the shape is crucial to the unique properties of water. When the two hydrogen atoms bond with the oxygen, they attach to the top of the molecule, so rather than being a linear molecule (H-O-H), the molecule is bent into a ‘V’ shape, usually shown with the O at the vertex. It is sometimes depicted looking a bit like Mickey Mouse. This V-shape gives water some unique properties, such as a relatively high boiling point, high specific heat, cohesion, adhesion, density, capillary action and evaporative cooling. Water molecules are constantly in motion, so this diagram is an exaggeration, but it is helpful to let you visualize the water molecule polarity.
Water molecules are called polar molecules, because they attract one another. Each water molecule has a slight positive charge on one end and a slight negative charge on the other, so the attraction of the opposite charges, (electro-static charges) creates what is called surface tension, the weak attraction is called a hydrogen bond. This molecular structure gives water a lopsided electrical charge that attracts other atoms. The end of the molecule with the two hydrogen atoms is positively charged. The other end, with the oxygen, is negatively charged. Just like in a magnet, where north poles are attracted to south poles (opposites attract), the positive end of the water molecule will connect with the negative end of other molecules.
Water polarity is responsible for several important properties of water, including ‘High specific heat’ allowing water to resists changes in temperature, as it must absorb a large amount of heat energy to increase in temperature which is better understood by knowing that not all substances are able to warm up at the same rate, hence you will notice different temperatures between the sand and water when you walk on the beach. Water also has a high heat of vaporization, which means that it can take a lot of heat without its temperature rising much. This plays a huge part in the climate, because it means that oceans take a long time to warm up.
‘Cohesion’ which makes water molecules “stick” together and ‘Adhesion’ which allows water molecules “stick” to many other materials because of hydrogen bonds. Adhesion and cohesion are water properties that affect every water molecule on Earth and also the interaction of water molecules with molecules of other substances. These properties make water kind of sticky, so that it is able to clump together into drops. Cohesion refers to the fact that water sticks to itself very easily. Adhesion means that water also sticks very well to other things, which is why it spreads out
Cohesion refers to the attraction of molecules for other molecules of the same kind, and water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another. Cohesive forces are responsible for surface tension, the tendency of a liquid’s surface to resist rupture when placed under tension or stress. The cohesion between water molecules is so strong that when they come in contact with another substance, such as air, the water molecules just below the air create a sticky surface skin, which is known as surface tension. Cohesion creates surface tension which is why if you fill a spoon with water, drop by drop, the water volume will actually be bigger than the spoon’s surface before the water falls off. Surface tension can also be seen if you fill a glass of water to the very top and then slowly add a few more drops, as before it overflows, the water forms a dome-like shape above the rim of the glass.
Water has a high surface tension and these bonds are so strong that they can support the weight of certain insects without sinking. The molecules on the surface of the water are not surrounded by similar molecules on all sides, so they’re being pulled only by cohesion from other molecules deep inside. These molecules cohere to each other strongly but adhere to the other medium weakly. One example of this is the way that water beads up on waxy surfaces. Surface tension makes these water drops round so they cover the smallest possible surface area.
Adhesion is the attraction of molecules of one kind for molecules of a different kind, and this adhesion property enables water to “climb” upwards through thin glass tubes (called capillary tubes) placed in a beaker of water. This upward motion against gravity, known as capillary action, depends on the attraction between water molecules and the glass walls of the tube (adhesion), as well as on interactions between water molecules (cohesion). The tendency of water molecules to stick to other molecules also allows water to dissolve substances, thus adhesive forces pull the water toward other molecules. Plants will suck up water, because the water adheres to the inside of the plant’s tubes, but the surface tension attempts to flatten it out. This makes the water rise and cohere to itself again, a process that continues until enough water builds up to make gravity begin pulling it back down.
We dipped our toes in to test the water and this captivating substance goes through stages of precipitation, evaporation, convection, condensation, it forms clouds, rain, snow, hail, fog, storms, vapor, moisture and rainbows. The water cycle describes how water evaporates from the surface of the earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation. Water is called a universal solvent because it dissolves more substances than any other liquid, and now this is all just water under the bridge.
Written for Ragtag Community – Water.