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AP®︎/College Biology
Course: AP®︎/College Biology > Unit 1
Lesson 1: Structure of water and hydrogen bonding- Hydrogen bonding in water
- Hydrogen bonds in water
- Capillary action and why we see a meniscus
- Surface tension
- Cohesion and adhesion of water
- Water as a solvent
- Specific heat, heat of vaporization, and density of water
- Importance of water for life
- Lesson summary: Water and life
- Structure of water and hydrogen bonding
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Lesson summary: Water and life
Key terms
| Term | Meaning | |
|---|---|---|
| Polar molecule | A neutral, or uncharged molecule that has an asymmetric internal distribution of charge, leading to partially positive and partially negative regions | |
| Cohesion | The attraction of molecules for other molecules of the same kind | |
| Adhesion | The attraction of molecules for other molecules of a different kind | |
| Density | The mass per unit volume of a substance | |
| Specific heat capacity | The amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius | |
| Heat of vaporization | The amount of energy needed to change one gram of a liquid substance to a gas at constant temperature |
Unique properties of water
- Water is polar. Water molecules are polar, with partial positive charges on the hydrogens, a partial negative charge on the oxygen, and a bent overall structure. This is because oxygen is more electronegative, meaning that it is better than hydrogen at attracting electrons.
- Water is an excellent solvent. Water has the unique ability to dissolve many polar and ionic substances. This is important to all living things because, as water travels through the water cycle, it takes many valuable nutrients along with it!
- Water has high heat capacity. It takes a lot of energy to raise the temperature of a certain amount of water by a degree, so water helps with regulating temperature in the environment. For example, this property allows the temperature of water in a pond to stay relatively constant from day to night, regardless of the changing atmospheric temperature.
- Water has high heat of vaporization. Humans (and other animals that sweat) use water’s high heat of vaporization to cool off. Water is converted from its liquid form to steam when the heat of vaporization is reached. Since sweat is made mostly of water, the evaporating water absorbs excess body heat, which is released into the atmosphere. This is known as evaporative cooling.
- Water has cohesive and adhesive properties. Water molecules have strong cohesive forces due 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. Water also has adhesive properties that allow it to stick to substances other than itself.These cohesive and adhesive properties are essential for fluid transport in many forms of life. For example, they allow nutrients to be transported to the top of a tree against the force of gravity.
- Water is less dense as a solid than as a liquid. As water freezes, the molecules form a crystalline structure that spaces the molecules further apart than in liquid water. This means that ice is less dense than liquid water, which is why it floats.This property is important, as it keeps ponds, lakes, and oceans from freezing solid and allows life to continue to thrive under the icy surface.
Common mistakes and misconceptions
- Water dissolves everything because it is the “universal solvent." Water has the ability to dissolve many substances but the term “universal solvent" is misleading. Water is able to dissolve other polar molecules and ions, such as sugars and salts. However, nonpolar molecules like oils lack partial positive or partial negative charges, so they are not attracted to water molecules. This is why nonpolar substances like oil remain separate when added to water.
Want to join the conversation?
So water is a covalent or ionic bond?(41 votes)
Water has a polar covalent bond, in other words, it is covalent but oxygen is more electronegative than hydrogen so it pulls the electrons to it, giving oxygen a slight negative charge and hydrogen a slight positive charge. Good question!(106 votes)
What is diffusion and give some examples(21 votes)
Diffusion is a type of molecular movement that brings water particles from places of high concentration to low concentration. There really are 4 different types. Simple Diffusion, Osmosis, Facilitated Diffusion and Active transport.(26 votes)
- I think water is a covelant bond(21 votes)
Yes, it is a polar covalent bond. That means that while the atoms are "sharing" the electrons, the oxygen hogs them a bit closer, creating a partial negative charge on that side of the molecule, and a partial positive charge on the Hydrogen side(39 votes)
- why is O electronegative?(18 votes)
To say that oxygen is electronegative fails to grasp the whole picture here. This is because ALL elements (except for the noble gases) are electronegative to some degree or other; ELECTRONEGATIVITY IS A PROPERTY OF THE ELEMENT which basically says "how strongly does it attract electrons?"
An element's electronegativity value is determined by a mixture of different factors, but the general rule is that it increases as you move right and upward across the periodic table. (Copy-&-paste this link for a visual: www.chemteacher.chemeddl.org/joomla/index.php?option=com_content&view=article&id=91)
So as for oxygen, (which was the subject of your question) it's electronegativity would indeed be one of the highest among all the elements because of where it is positioned in the periodic table (but more specifically because the factors that I alluded to earlier are manifest for oxygen in such a way as to make it such).(26 votes)
I still don't quite get the meaning of adhesion and cohesion, and the difference between them. Can somebody help me out?(12 votes)
adhesion is an attraction to unlike molecules, and cohesion is an attraction to like molecules.(29 votes)
- which property allow solid ice to flot in liquid water(12 votes)
- One property of water is that it crystallizes when it freezes, that is it arranges itself in a particular formation whenever it freezes. This formation happens to be less dense than its structure when it is in liquid form. It is this property that allows ice to float. Hope this helped!(20 votes)
I'd like to know about the different types of bonds, like Sal mentioned Ionic Bonds, Covalent Bonds and Hydrogen Bonds, but what exactly are they?(11 votes)
A Covalent Bond is where atoms share eletrons, A ionic is an atom steals an eletron from another atom, giving it to the opposite charge, thus the atoms are attracted to each other. A Hydrogen Bond: A weak bond betweeen to molecules resulting from an electrostatic atrraction between a proton in one molecule and an electronegative atom in the other. Hope this helps,(16 votes)
- I have a question, what will happen if acids, fire and water combine together?(11 votes)
Its not as exciting as you think it would be. if you put something like lemon juice on a fire, it will most likely go out, same with water. I hope this helps.(6 votes)
what exactly is an ion(7 votes)- an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion), which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion), which is created by an electron gain and is attracted to the anode.(12 votes)
Are there any exceptions to the "like dissolves like" rule? (ex: polar molecules being able to dissolve non-polar molecules)(10 votes)- Good question! Water is capable of dissolving certain nonpolar substances, but not very well.(5 votes)
