Name: water molecules and surface tension
Uploaded: 2019-03-11T09:21:00.000Z
Duration: 1 min 7 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Systems

ESS.EES.3.1

Cohesion

Kohäsion ist die Tendenz, dass ähnliche Moleküle Bindungskräfte erzeugen.
 Wasser ist ein klassisches Beispiel.
 Mehrere Moleküle bilden Tröpfchen, indem sie über Wasserstoffbrückenbindungen kohäsiv angezogen werden.
 Wenn die Tropfen sich sammeln, werden einige Moleküle an der Oberfläche Luft ausgesetzt.
 Bei einem Mangel an geeigneten Substanzen, um an dieser Grenzfläche zu binden, wird Wasser mehr von sich selbst angezogen, und erzeugt einen inneren Sog.
 Eine solche Anziehung baut viele Bindungen auf und erzeugt eine Oberfläche, die Brüche verhindert, wenn es zu Spannungen kommt, dieses Phänomen heißt Oberflächenspannung.
 Folglich können kleine Objekte auf dem Wasser laufen, solange sie nicht die wirkenden Kohäsivkräfte brechen.

Yang, Eunjin, Jae Hak Son, Sang-im Lee, Piotr G. Jablonski und Ho-young Kim. "Wasserläufer passen die Bewegungsgeschwindigkeit der Beine an, um die Startgeschwindigkeit für ihre Morphologie zu optimieren." Nature Communications 7 (7. Dezember 2016). [<a href="https://doi.org/10.1038/ncomms13698">Quelle</a>]

kohäsion

Kohäsion ist die Anziehung zwischen Molekülen der gleichen Art wie zum Beispiel Wassermolekülen. Der teilweise geladene negative Sauerstoff eines Wassermoleküls bindet sich an den teilweise positiv geladenen Wasserstoff eines zweiten Wassermoleküls durch eine Wasserstoffbrückenbindung. Jedes Wassermolekül kann mit anderen Wassermolekülen bis zu vier Wasserstoffbrückenbindungen eingehen.
 
 Wenn auf einer Oberfläche mehrere Wassermoleküle durch Kohäsion aufeinandertreffen, bildet sich ein Tropfen. Wasser breitet sich typischerweise nicht über eine Oberfläche aus. Das liegt daran, dass die Wassermoleküle stärker voneinander angezogen werden als von den Molekülen der Oberfläche oder der umgebenden Luft.
 
 Die Kohäsion erzeugt eine Oberflächenspannung. Teichläufer oder auch Wasserläufer genannt, sind Insekten, die sich dieses Phänomen zu Nutze machen, um auf Wasser laufen zu können. Die Oberflächenspannung entsteht an der Grenzfläche zwischen Wasser und Luft (d.h. der Oberfläche des Wassers). Auch hier werden die Wassermoleküle stärker voneinander als von den Molekülen in der Luft angezogen. So bilden die Wassermoleküle an der Oberfläche Bindungen mit benachbarten Wassermolekülen neben und unter ihnen aus. Da die Wassermoleküle an der Oberfläche keine Bindungen mit anderen Wassermolekülen auf einer Seite (der luftnahen Seite) eingehen können, bilden sie stärkere Bindungen mit ihren benachbarten Wassermolekülen aus. Die stark gebundenen Moleküle haben eine verdichtete Oberfläche, wodurch kugelförmige Wassermolekültröpfchen entstehen. Die hohe Oberflächenspannung des Wassers und der Auftrieb der Beine des Teichläufers ermöglichen es dem Insekt, sich auf der Wasseroberfläche zu bewegen.
 
 Quecksilber ist ein weiteres kohäsives Molekül, das man leicht erkennen kann. In einem Glasbehälter breitet sich das Quecksilber nicht aus und benetzt das Glas nicht, da die Kohäsionskräfte zwischen den Quecksilbermolekülen stärker sind als die Haftkräfte zwischen Quecksilber und dem Glas. Obwohl Wasser sehr kohäsiv ist, hat es auch eine Affinität zu Siliziumoxid. Daher verteilt sich Wasser gleichmäßig am Boden eines Glasbehälters.

Kohäsion

Kohäsion ist die Anziehungskraft zwischen Molekülen des gleichen Typs, wie z. B. Wassermolekülen. Wassermoleküle haben eine neutrale Ladung, sind aber polar ...

Education

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JoVE Core

Biology

Biologie

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Grundlagen

Chemistry of Life

Chemie des Lebens

KEY TERMS AND CONCEPTS

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water molecules and surface tension

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature.

Cohesion helps water form droplets on a surface. Water does not usually spread out because the water molecules are more attracted to each other than to the surface or the air around them. The attraction between water molecules at the surface and the bulk water is called surface tension, and it comes from cohesion. At the water-air boundary, surface molecules can only make hydrogen bonds beside and below them. That limited bonding creates a compressed surface area and spherical droplets.

Surface tension is strong enough to support pond skaters, also called water striders. These insects use the surface of water to walk across it. Their buoyant legs and the high surface tension of water help them stay on top of the water.

Mercury is another cohesive liquid. In a glass container, mercury stays in spherical droplets because the cohesive forces between mercury molecules are stronger than the adhesive forces between mercury and glass. Water is also highly cohesive, but it has an affinity for silica, which is a main component of glass. Because of that, water spreads evenly at the bottom of a glass container.

Water Molecules and Surface Tension

the periodic table and organismal elements

the-periodic-table-and-organismal-elements

Periodic Table Basics for Living Things

The periodic table helps explain which elements living things need and how those elements are related. Elements are the smallest units of matter that cannot be broken down further by chemical processes. There are 118 known elements, but not all occur naturally, and even fewer are essential for life. Living matter is made mostly of carbon, nitrogen, hydrogen, and oxygen. Together, these elements make up most of the human body and are also found in all life on Earth. Smaller amounts of calcium,...

atomic structure

Atoms and Their Subatomic Particles

Atoms are the smallest units of elements, and they make up all matter. Each atom contains three subatomic particles: protons, neutrons, and electrons. These particles give an atom its mass and its charge. The idea that matter is made of tiny particles goes back to Democritus, a Greek philosopher around 450 B.C. He used the word atomos, which means “indivisible.” The idea was not accepted at the time, but it returned many centuries later. In the 19th century, John Dalton proposed an atomic...

isotopes

Atomic Mass and Isotope Basics

Atomic mass and isotopes are linked by the number of protons and neutrons in an atom. The number of protons sets an element’s atomic number, or Z. For example, every atom with eight protons is oxygen. Atoms of the same element can still differ because they can have different numbers of neutrons. The mass number, or A, is the total of protons and neutrons. Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have several isotopes. Carbon-12, carbon-13,...

electron behavior

Electron Shells and Valence Electrons

Electrons are negatively charged subatomic particles that occupy regions around the positively charged nucleus of an atom. Their location is linked to energy levels called shells. They are also grouped into sub-shells and orbitals within each shell. An electron’s shell shows its general energy level. Electrons closer to the nucleus have less energy, while electrons farther away have more energy. The sub-shell gives a more exact location and energy level. An orbital is the shape of the region...

electron orbital model

Electron Orbitals and Energy Levels

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covalent bonds

Electronegativity and Covalent Bond Polarity

Covalent bonds form when two atoms share electrons to fill their valence shells. The way those shared electrons are pulled depends on electronegativity, which is an atom’s ability to attract electrons in a bond. When atoms have similar electronegativities, they form nonpolar covalent bonds. When their electronegativities differ, the bond is polar because the electrons are shared unevenly. The number of covalent bonds an atom can make depends on its valence electrons. Oxygen has six valence...

ionic bonds

Ionic Compounds and Electrolytes

Ionic compounds form when atoms gain or lose electrons to reach a more stable electron configuration. The charged particles that result are called ions. Ionic bonds are electrostatic attractions between oppositely charged ions. The most reactive elements include those with one valence electron, such as potassium, and those that need one more valence electron, such as chlorine. Ions that lose electrons become positive cations. Ions that gain electrons become negative anions. Cations and anions...

hydrogen bonds

Hydrogen Bonds in Water

Hydrogen bonds in water are weak attractions between atoms that are already part of other chemical bonds. One atom is electronegative, such as oxygen, and carries a partial negative charge. The other is a hydrogen atom that is bonded to another electronegative atom and has a partial positive charge. These attractions form because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom like oxygen or nitrogen. The electrons in that bond are shared unequally.

van der waals interactions

Intermolecular Forces in Polar Solutions

Intermolecular forces are the attractions and repulsions that act between atoms and molecules. These electrostatic forces come from particles with permanent, partial, or temporary charges. For neutral atoms and molecules, the main types are ion-dipole, dipole-dipole, and dispersion forces, which are together called van der Waals forces. Polar molecules have a partial positive end and a partial negative end. That separation of charge creates a dipole. In water, oxygen is more electronegative...

elements and compounds

Elements, Compounds, and Bonding

Elements and compounds are the two main kinds of pure substances. A pure substance contains only one kind of matter. An element contains only one type of atom. A compound contains two or more types of atoms joined by a chemical bond. Elements can be atomic or molecular, depending on their basic units. They are unique forms of matter with specific chemical and physical properties. Ordinary chemical reactions cannot break an element into a smaller substance. There are 118 elements, but only 98...

molecular shapes

Electron Geometry and Lone Pairs

Electron geometry and lone pairs help explain why molecules take specific shapes. The arrangement of electron groups around a central atom controls the molecular geometry. Valence electrons form bonding pairs, which sit mainly between bonded atoms, or lone pairs, which belong to one atom only. Electron pairs in the valence shell spread out to reduce repulsion. They do this by maximizing the distance between one another. A diatomic molecule has two regions of electron density, and these are...

pH Scale in Everyday Solutions

pH measures how acidic or basic a water-based solution is. It depends on the concentration of hydronium ions, H3O+, in the solution. In one liter of pure water at neutral pH, there are 1×10−7 moles of hydronium ions. Because hydronium ion levels can vary over a very wide range, measuring pH directly in moles is not practical. The pH scale converts hydronium ion concentration into a negative logarithm. Pure water has a pH of 7 and is neutral. Most solutions fall between 0 and 14, but some, such...

chemical reactions

Atoms, Bonds, and Chemical Reactions

Chemical reactions rearrange atoms to form new substances. In a reaction, the starting materials are called reactants, and the new substances are called products. The atoms stay the same type and number, but their bonds change, so the substances become different compounds. During a chemical reaction, bonds between atoms break and form again. This means the shared electrons are rearranged. Some reactions happen on their own, while others need an energy source such as heat or light. In biology,...

redox reactions

Electron Transfer in Redox

Redox reactions are chemical reactions that involve electron transfer between atoms or molecules. When one particle gains electrons, another must lose them at the same time. That is why oxidation and reduction always happen together. The two roles in a redox reaction are linked. The atom that is oxidized acts as the reducing agent, or reductant. The atom that is reduced acts as the oxidizing agent, or oxidant. A simple way to remember the ideas is OIL-RIG, which means oxidation is losing...

cohesion

Water molecules stick to each other through cohesion. Water is neutral overall, but it is a polar molecule. The oxygen atom in one water molecule has a partial negative charge, and it can bind with a hydrogen atom that has a partial positive charge in another water molecule. This forms a hydrogen bond. Each water molecule can form up to four hydrogen bonds with other water molecules, and these bonds give water its cohesive nature. Cohesion helps water form droplets on a surface. Water does not...

adhesion

Water Climbing by Adhesion

Water can climb or stick to surfaces because of adhesion, which is the attraction between different kinds of molecules. In water, this is easy to see on polar surfaces such as glass or cellulose in plants. The positive hydrogen side of water is more attracted to the negative oxygen in silica than to nearby water molecules. This attraction helps explain capillary action. If a narrow glass tube is placed in a beaker of water, water molecules attach to the tube’s surface and the water level rises.

states of water

Water Phase Changes and Ice Density

Water changes between solid, liquid, and gas states as temperature and molecular motion change. In this lesson, the focus is on how water freezes, melts, vaporizes, and returns to liquid or solid form. The balance between intermolecular forces, which pull molecules together, and kinetic energy, which pushes them apart, controls each state. Water freezes when intermolecular forces become stronger than kinetic energy. Unlike most substances, ice is less dense than liquid water. This happens...

specific heat

How Specific Heat Affects Temperature

Specific heat capacity describes how much energy a substance needs to rise by 1 degree Celsius for each gram. It is often written with calories, grams, and degrees Celsius, but it can also be shown in joules, kilograms, and Kelvin. For water, 1 gram needs 1 calorie to increase by 1°C, which is also written as 1 cal/g-°C or 4186 J/kg/K. Water has a high specific heat capacity, so it takes in a large amount of heat before its temperature changes much. It also gives off a lot of heat when it...

vaporization

Vaporization, Boiling, and Evaporation

Vaporization changes a liquid into vapor when temperature adds enough kinetic energy to overcome intermolecular forces. It is a surface phenomenon, which means it starts at the liquid’s surface. The energy needed to vaporize a set amount of liquid at a given pressure and constant temperature is called the heat of vaporization. Water shows this process clearly. When liquid water is vaporized, it becomes steam. One way this happens is boiling, which occurs when vapor bubbles form beneath the...

solvents

Water as a Biological Solvent

Water acts as a biological solvent in many living systems. A solvent is a substance, usually a liquid, that dissolves another substance called a solute. When a solvent and a solute mix, they form a solution, which is a uniform mixture of both parts. Water is called a universal biological solvent because its polar structure helps it dissolve many other polar compounds. Polarity means that one side of the molecule has a slight positive charge and the other side has a slight negative charge.

carbon skeletons

Carbon Backbones in Biomolecules

Carbon backbones give biological molecules their structure and flexibility. Living things are built from macromolecules that contain carbon atoms, and organic compounds are defined by a carbon backbone. Carbon is tetravalent, so each carbon atom can bond with four other atoms. Its valence electrons are stable, so carbon rarely becomes an ion. As carbon chains get longer, they can form ring structures, double bonds, and branching side chains. Carbon-carbon bonds create the carbon skeleton.

key terms and concepts

Learn how water molecules bond through cohesion, create surface tension, form droplets, and help pond skaters walk on water in this high school science topic.

Water Molecules and Surface Tension | JoVE K12

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Pennsylvania State Academic Standards

Earth and Space Science

3.3.9-12.K

Louisiana Student Standards for Science

High School

Earth Science

Earth’s Systems

HS-ESS2-5

Alabama Course of Study Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

9-12.B.1.4.b

Florida Department of Education

Life Science

SC.912.L.18

SC.912.L.18.12

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Water Molecules and Surface Tension

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