van der waals force

how to study certain subjects

hi everyone! i took biology, chemisty, mathematics and economics for my a levels, and i’d like to share with you how i studied these subjects!

keep in mind that this is what worked for me, and i hope it works for you too! note that i’m a 2nd year college student so my memory of these stuff might be a little fuzzy. c’:

i will also only be covering everything but economics because up till now, i have no idea how to study for economics lololol.

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Requested by @pokecrettes

The human body temperatures is, on average, 98.6 degrees Fahrenheit (or 37 degrees Celsius). Many animals have different ranges. Goats, for example, have a normal range about 102 degrees Fahrenheit (40° C) while some lizards are best as low as 75 degrees fahrenheit (24° C). Some lava pokémon, such as Magcargo or today’s Heatran, have a body temperature significantly higher than that.

Heatran, for example, is a fire-steel type. According the the pokédex, it is made of rugged steel, but is partially melted in spots because of its own body heat. Steel is a combination of iron and other metals, usually carbon. By mixing iron with other metals, steel forms a stronger, more resistant, less corrosive material. It depends on the mixture, but steel typically melts around 1370 degrees Celsius (2500° F). However, steel will start to deform or “soften” at 538 degrees Celsius (1,000° F). This means that if Heatran’s steel is deformed because of its heat, its body temperature must be at least 1000°F.

Fresh lava, for comparison, has a temperature between 1,300° F and 2,200° F. So, Heatran’s body temperature is nearly the same as its environment, since it dwells in volcanic caves. Besides needing to survive its environment, why is Heatran so hot?

For humans, it turns out 98.6° F is a perfect balance. It’s hot enough that most fungus can’t live and thrive in our body, but cool enough that it doesn’t take too much energy to upkeep the temperature. Our metabolism, which includes the process of turning food into energy, is more or less efficient depending on an animal’s body temperature. 

Here’s a graph comparing the metabolism of two animals, a mouse and a lizard. Different body temperatures are on the horizontal axis, and energy outputs are on the vertical axis. The mouse, a mammal like us, has a metabolism that works the best at around 38 degrees Celsius. A lizard, on the other hand (a cold-blooded animal), puts out less energy over all, but is efficient at a much wider range of body temperatures. A lizard could be 20° C or 30° C and not suffer much difference in energy output. A mouse on the other hand has a fairly small window.

An animal’s body temperature is all about determining that balance between health and metabolism. The fact that Heatran’s body temperature is so high may tell us a few things. Most bacteria, for example, can’t even survive at temperatures higher than 50° C (122° F). A little higher than that, about 75° C (167° F), is enough to kill most viruses like influenza. Even for the crazy thermophile bacteria that live in hot environments like ocean vents, the “world record” is 113° C (235° F). Heatran’s body temperature is at least 5 times that. Its hot body temperature means that Heatran doesn’t even need an immune system. Its body is way too hot to support most life, including the good bacteria humans have naturally that help us digest food. 

In fact, temperatures as hot as Heatran kill most life of any kind. Heatran must have some weird systems to be most efficient in those temperatures. Not to mention that he is made out of steel.

Heatran’s body temperature is around 1000°F (538° C). Heatran’s metabolism is most efficient at higher temperatures, and it does not need an immune system because the heat kills any fungus, bacteria, or virus that may want to infect Heatran.

Another part of Heatran’s entry tells us that it is capable of climbing on ceilings and walls. Insects, frogs, spiders and geckos are all known to be able to cling to smooth surfaces and walk on walls or upside down like Heatran. The secret is their feet are covered in hundreds of tiny hairs called setae.

These tiny hairs grip to small irregularities on surfaces, such as pores, small holes, or ridges. These hairs are tiny enough that when gripping into regularities like this, their molecules will interact and a small electromagnetic force called the van der Waals force kicks in. Each hair is capable of creating a force of about 6 picoNewtons, and it takes about 20.1 Newtons to keep the gecko from falling off of the wall.

Heatran weighs a bit more than your standard gecko though, at 430.0 kg (948 lbs). The pokédex tells us that Heatran digs into walls with it’s cross-shaped feet. Perhaps its feet have thousands of tiny setae like a gecko’s, or perhaps it uses its heat to its advantage. Heatran is hot enough that it could melt into the walls with its feet, making itself adhesive that way.

Geckos: Sticky Business

How geckos stick to surfaces has been a point of serious interest for some time to many scientists. Yet the solution continues to evade them and to prove more complex than first though. Their interest persists though because nature has been been working on these problems for the better part of 4.5 billion years and we could learn a lot from her! Mimicking nature is, unsurprisingly, called biomimickry and is a very useful tool in science. If we could figure out how to stick over and over again with the ease of the gecko it would be quite the achievement.

Scientists haven’t been idle twiddling their thumbs over the decades; it was first posited in 1934 that electrostatic forces may be the force behind the adhesive property of gecko. A researcher W.D. Dellit subjected the air surrounding the toes of the gecko to x-rays in order to neutralise any charges. He believed that this should have caused the gecko to fall if it were attached via electrostatic forces, however this did not occur. This lead him to conclude that the gecko must be employing another trick of nature.

Having crossed off electrostatic forces, curious minds across the world moved on and just over a decade ago a paper was published asserting that the adhesive property of geckos are due to van der Waals forces. These forces exist between touching surfaces such as a smooth windowpane and a gecko’s toes. But now, a new paper suggests that scientists were too hasty in ruling out electrostatic forces. Their first port of call is the adhesive force between the gecko and various surfaces. In their research they found that geckos can exert twice the adhesive force on Teflon AF than to polydimethylsioxane; these two materials are very similar in structure which made this result surprising. This lead the researchers to conclude that van der Waals are not the only forces at play.

Their second reason comes from a deeper understanding of how x-rays interact with their surroundings. The 1934 researcher, Dellit, was correct in saying that the x-rays should neutralise any electrical charges on the surface but did not know that the gaps between the grip pads on the gecko’s toes were too small to allow the ionized air particles between them. Thus the electrical charges would not have been neturalised.

It is also noted by other scientists that geckos have no trouble sticking to surfaces upon which electric charges do not accumulate, eg. bare steel and underwater. Thus it is noted that constant electrification does not seem to be necessary for adhesion. As the mystery deepens, the scientists realise that they have their work cut out for them in figuring out this complex problem.

{Citations}

Exotic atomic threesomes explained

How an experiment confirmed giant quantum states of three atoms that would not bind in twos.

In 1970 Vitaly Efimov, a physicist now at the University of Washington in Seattle, found a surprising effect hidden in the equations of quantum physics.

He calculated that when two identical particles interact too weakly to form bonds, a third one can reinforce their interaction and keep the three particles together in a stable, if loosely bound, state1. This should apply to neutral atoms, whose mutual attraction (known as Van der Waals force) can be extremely feeble.

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Geckos Go To Market

Geckos, the lizards whose amazing toes let them adhere to almost any surface, may just be the poster animals for innovation in 2015. Everywhere you look, the little creatures are inspiring engineers and materials scientists to push the envelope on new adhesives and coatings.

Earlier this year, Stanford showed off a robot that could pull 100 times its own weight using gecko physics. NASA has also announced it will use robots with feet like the lizard’s to crawl around the outside of the International Space Station for inspection and repair. There’s even a system being developed to let people strap on foot and hand pads to be like Spider-Man.

Now a Carnegie Mellon University spinoff company called nanoGriptech has announced that it is launching the first commercially available gecko-inspired adhesive into the market. The company says their dry coating can be used in manufacturing, medical settings, in safety and defense applications and even for better soccer goalkeeper’s gloves. 

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1.2.2: Bonding

Ionic bonding: the electrostatic attraction between oppositely charged ions.

Ionic boning is usually found in compounds made of a metal and a non-metal. The metal loses electrons and forms a positive ion, the non-metal gains electrons and forms a negative ion. Dot and cross diagrams can be drawn for ionic compounds, showing the simplest whole number ratio - e.g. NaCl would show one Na⁺ ion and one Cl⁻ ion, and MgCl₂ would show one Mg²⁺ ion and two Cl⁻ ions. 

The arrangement of ions in an ionic solid is described as a giant ionic lattice, as the ions all fit together in a regular pattern:

This structure gives ionic substances many of its properties:

  • High melting and boiling points: because the electrostatic attraction between the +ve and -ve charges  is very strong. Also, the larger the charges of the ions are, the stronger those attractions are the higher the melting point/boiling point will be. 
  • Conduct electricity only when molten or dissolved: because the +ve/-ve ions are fixed in place in the lattice when solid, there are no mobile charge carriers, and thus nothing to conduct electricity. However when molten or in solution, the ions can move and carry charge, thus it conducts electricity. 
  • Soluble in water: because the δ- charge on the oxygen and the δ+ on the hydrogen of the water molecule are attracted to the + and - charges of the ions, and this attraction is strong enough to pull the ionic lattice apart. 
  • Brittle: when a force is applied to an ionic substance, the lattice is deformed and ions with like charges will become aligned. Like charges repel, and this repulsion is enough to split the crystalline structure

Covalent bond: a bond formed by a shared pair of electrons

A group of atoms bonded covalently is called a molecule, and these can also be shown through dot and cross diagrams. Because the electrons are shared, not taken, they look different to ionic dot and cross diagrams. 

Rules for forming covalent bonds:

  1. Unpaired electrons pair up
  2. The maximum number of electrons that can pair up is equal to the number of electrons in the outer shell. 

There are two types of pairs of electrons, ones that are being used in a bond, known as bonding pairs, and ones that aren’t shared, known as a lone pair. 

Lone pair: a pair of electrons in the outer shell not used in bonding. 

Mostly, covalent bonds are formed by each bonding atom donating one electron. In some cases, one atom donates both electrons to the bond. This is known as a dative covalent or coordinate bond. 

Dative covalent (coordinate) bond: a bond formed by a shared pair of electrons which has been donated by one of the bonding atoms only. It can be written as A—>B, with the arrow indicating the direction in which the electron pair has been donated.

Some substances may be a mix of covalent and ionic bonding, like MgCO₃:

There are two kinds of covalent structure: simple molecular and giant covalent lattice. 

Simple molecular: a 3 dimensional structure of molecules, held together by weak intermolecular forces 

  • Simple molecular structures have low boiling points, because the intermolecular forces are van der Waals’ forces and relatively weak, so little energy is needed to overcome them. 
  • They don’t conduct electricity because there are no charged particles that are free to move
  • They are soluble in non-polar solvents, because van der Waals’ forces form between the simple molecular structure and the non-polar solvent. 

Giant covalent lattice: a 3 dimensional structure of atoms, bonded together by strong covalent bonds

  • They have high melting and boiling points because the strong covalent bonds between the atoms require a high amount of energy to overcome
  • They don’t conduct electricity (apart from graphite) because there are no charged particles free to move
  • They’re insoluble in both polar and non-polar solvents because the covalent bonds are too strong to be overcome. 

Diamond and graphite are two allotropes of carbon.

Allotrope: two or more different forms in which an element can exist

Diamond:

  • has a tetrahedral structure held together by covalent bonds
  • it’s not an electrical conductor because there are no delocalised electrons to carry charge; all the outer-shell electrons are used to form bonds
  • it’s hard because the tetrahedral structure allows external forces to be spread throughout the lattice. 

Graphite:

  • has strong hexagonal layers, covalently bonded, with weak van der Waals’ forces between them 
  • it conducts electricity because there are delocalised electrons between the layers, that can move parallel to them and carry a charge
  • it’s soft because the bonding within each layer is strong, but the forces between each layer are weak and allow them to slide easily. 

Metallic bonding: the electrostatic attraction between a lattice of positive ions and a sea of delocalised electrons. 

Metallic substances don’t bond covalently or ionically, and this gives them different properties to ionic or covalent substances:

  • High melting/boiling points: there’s strong electrostatic attraction between the positive lattice and negative sea, that requires a lot of energy to overcome
  • They conduct electricity well: thanks to the sea of delocalised electrons, which can move and carry a charge. When molten, the ions can move too. 
  • They’re insoluble in water or non-polar substances because the electrostatic attraction is too strong for the interactions with the solvents to overcome

nenineni-bububu  asked:

What make glue sticky?

This is on the face of it a pretty simple question, but the chemistry behind it is actually a little complicated. It’s also complicated further by the fact that different glues will work in different ways.

As one example, superglue contains the chemicals from the cyanoacrylate family, one of which, methyl cyanoacrylate, is shown below. This chemical rapidly polymerises (forms long chains) with other molecules of itself when it comes into contact with moisture - even the moisture in the air is enough to start this process. The polymerisation bonds the joined surfaces together. So, when you get superglue on your skin, the ‘stickiness’ is caused by the polymerisation, set off by the moisture in your skin.

Other types of glue can stick things together in different ways. Even an object that feels smooth will have a very rough surface on a molecular level, and liquid glue can seep into microscopic cracks in an object’s surface. ‘Mechanical bonding’ sticks the two objects together as the glue hardens within these crevices.

Intermolecular forces also play a part in the ‘stickiness’ of glue, in particular Van der Waals forces. Electrons in molecules are mobile, and at any point in time there could potentially be more electrons at one end of the molecule than at the other. This leads to what we call a ‘temporary dipole’ - meaning the molecule has one slightly positively charged end, and one slightly negatively charged end. Because electrons in molecules are constantly moving, temporary dipoles are constantly being created. 

If molecules with temporary dipoles get close enough to other molecules, they can create temporary dipoles in those molecules too. These are known as ‘induced dipoles’. In order for this to occur though, the molecules have to be very close together, no more than a few angstroms. An angstrom is a unit of measurement equal to 0.00000001cm. This is why glue being wet is important - so it can spread and flow to ensure this close contact. So, molecules in the adhesive can induce temporary dipoles in the molecules of the surface it is sticking to, increasing the strength of mechanical bonding.

This is as much as I’ve been able to dig up on the subject. If anyone has anything else to add, I’d be very interested to hear it!

References & Further Reading