Monthly Archives: May 2014

Cool Story BrO-

Q. Want to hear a joke about sodium?

A. Na.

Q. Want to hear a joke about sodium hypobromite?

A. NaBrO.

Chemists deal with lots of strange-sounding materials like sodium, ytterbium, and potassium hexacyanoferrate(III), so they’ve developed a system of symbols and formulas to represent these materials. The elements of the periodic table all have one- or two- letter symbols*. In some cases the symbol obviously descends from the element’s name; to wit, the symbol for oxygen is O, the symbol for titanium is Ti, and the symbol for chlorine is Cl.

Some elements – particularly the elements that have been known since antiquity – have symbols that do not seem logically connected to their name. In these cases, the symbol usually refers to an older name for the element, perhaps from Latin or Greek. For example, the symbol for sodium, Na, comes from the Latin word natrium. The word natrium has an even deeper, richer history among the alchemists and scholars of the ancient world, or so says Elementymology & Elements Multidict, a most fascinating site if you’ve got a few minutes to spare. At any rate, in 1807, Sir Humphrey Davy isolated the metal and recognized it as a distinct element. Bucking centuries of tradition, Sir Davy decided the metal ought to be named sodium, for he isolated it from caustic soda (now known as lye or sodium hydroxide).

So what about sodium hypobromite? Sodium hypobromite is a compound that contains sodium, bromine, and oxygen. Bromine and oxygen combine to form a group called a polyatomic ion. Since this group has an overall negative charge, it bonds quite easily with positively-charged sodium ions.

Bromine is fairly versatile as far as bonding with oxygen goes; there are actually several polyatomic ions made of bromine and oxygen. They are distinguished by the number of oxygen atoms bonded to the bromine atom, and by small variations in their names. Here are four compounds that can be made from the same three elements, and their names:

  1. NaBrO = sodium hypobromite
  2. NaBrO2 = sodium bromite
  3. NaBrO3 = sodium bromate
  4. NaBrO4 = sodium perbromate

If one isn’t too picky about capitalization, one could read NaBrO as “Na, bro”, meaning “No, close male associate (or perhaps my biological brother), I do not wish to hear a joke concerning sodium hypobromite.” Of course, the person already indicated his disinterest in hearing a joke about sodium. Perhaps this fellow simply isn’t in the mood for chemistry-themed jokes. We’ve all had days like that.


*Some periodic tables have three-letter symbols for the last few elements. These symbols represent temporary names. When the International Union of Pure and Applied Chemistry, or IUPAC, assigns permanent names to these elements, they will get a traditional one- or two-letter symbol to go along with their name.

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Chemists and Plumbers

Q. How can you tell the difference between a chemist and a plumber?

A. Ask them to pronounce “unionized”.


Yeah, that might work. Here are some other nifty ways to tell the difference between a chemist and a plumber.

  1. Ask “Are you a chemist or a plumber?”
  2. Observe their appearance: plumbers wear coveralls and carry large pipe wrenches; chemists wear lab coats and carry beakers.
  3. Where did you see them? Plumbers come to your home in trucks, then shimmy through the crawl space. Chemists are usually found in laboratories. They seldom visit your home on business and they almost never shimmy.

When asked to pronounce the word unionized, a plumber would probably say “YOON-yun-ized”, as in belonging to a labor union. Labor unions are worker advocacy groups and are present in many professions. They try to protect worker rights and settle disputes between the labor and management.

A chemist would be more likely to say “un-EYE-on-ized”. In order to understand the meaning of unionized, you have to know the meaning of ionized. A molecule or atom is ionized when it acquires a positive or negative charge. This can happen when it loses or gains electrons. We’ve talked about this before. Acids and bases can also become ionized, not by gaining or losing electrons, but by splitting into charged pieces.

Consider hydrogen chloride, HCl. In its pure form, HCl is a noxious, colorless gas. The hydrogen atom and the chlorine atom share a pair of electrons; a covalent bond. The molecule as a whole is neutral, meaning it has an equal number of protons and electrons and no net charge.

When HCl dissolves in water, it changes. The hydrogen separates from the chlorine, but chlorine keeps both of the shared electrons. This leaves the hydrogen ion bereft of electrons, resulting in an overall positive charge. The chloride ion, for its participation, acquires a net negative charge. In this way HCl splits into ions without actually gaining or losing electrons.

HCl → H+ + Cl

The liberated H+ ions are absorbed by water molecules, resulting in the formation of another ion: the hydronium ion, H3O+. Hydronium ions are the defining characteristic of aqueous acidic solutions. Any acid, dissolved in water, will yield hydronium ions.

H+ + H2O → H3O+

Bases also react with water molecules to produce ions. Instead of hydronium ions, bases produce hydroxide ions, OH. Consider the reaction of ammonia, NH3, a base, with water:

NH3 + H2O → NH4+ + OH

But we’re not talking about ionized molecules, we’re talking about unionized molecules. That part’s simple: an unionized molecule is any molecule that hasn’t been ionized. Yeah, I know: I could have just said that from the start. But you’ve got to have the foundation before you can get the joke. Right?


A Pascal Pun

Albert Einstein, Isaac Newton, and Blaise Pascal are playing Hide ‘n’ Seek. It’s Einstein’s turn to count, so he covers his eyes and counts to ten. Pascal runs to hide, but Newton draws a one meter by one meter square on the ground, then stands in the middle of it.

Einstein reaches ten and uncovers his eyes. He sees Newton immediately and exclaims “I found you, Newton! You’re it!”

Newton replies “You didn’t find me. You found a Newton over a square meter. You found Pascal!”


Oh, that rascally Newton. Or should I say, that Pascally Newton?

No, I probably shouldn’t.

Anyway, let’s talk about pressure. Not the emotional pressure of having to meet a deadline, or peer pressure, but fluid pressure. Fluids, like air or water, are drawn towards the center of Earth just like everything else on this planet due to the influence of gravity. These fluids exert their weight on anything beneath them. We experience this weight as pressure.

Unlike the weight of a solid object, pressure doesn’t just push downward; it pushes in all directions. Here, at the bottom of Earth’s atmosphere, you have almost fifteen pounds of force pushing inward on every square inch of your body. A square inch is roughly the area of a postage stamp, so the average human body has a lot of square inches to it. Using the Du Bois formula, we can estimate that a 75-kilogram man (165 pounds) who is 178 cm tall (5′ 10″) ought to have a body surface area of about 1.9 square meters (about 3000 square inches). If that man is at or near sea level, he’ll have nearly 20 metric tons (22 short tons) of force pushing inward.

Now hold on, I hear you saying. If we’re all subject to multiple tons of force, pushing inward from all directions, why don’t we all get squished like bugs?

There are several reasons:

  1. We’re adapted to survive under this pressure.
  2. We’re full of fluids that are pushing outward with equal force.
  3. Most of the stuff inside us is fairly incompressible anyway.

So don’t worry too much about it. Just think about how amazing you are for standing up to that kind of pressure. Go you.

What do Newton, Einstein, and Pascal have to do with any of this? Well, for all of his accomplishments, Einstein is not really necessary to this joke. You can replace him with your favorite scientist; say, Alfred Wegener.

A newton (after Sir Isaac Newton, in case there was any doubt) is the metric unit of force (not pressure, and it’s important to make this distinction!) A force is a push or pull, and for all intents and purposes a force acts on a single point. Pressure, on the other hand, is a force spread out over an area. When you walk about pressure using metric units, you talk about newtons per square meter.

The metric unit of pressure is the newton per square meter, or N/m2. There’s another, shorter name for this unit: the pascal (abbreviated Pa). One pascal is exactly equal to one newton per square meter, and the two terms are used interchangeably. So, by standing on an area of one meter by one meter (a square meter), Newton made himself a Pascal. Cute.


Halloween and Christmas

Q. Why do computer scientists confuse Halloween and Christmas?

A. Because Oct 31 = Dec 25


Yes, it’s another joke about number systems. Perhaps you’ll recall a time not so long ago when we discussed the merits of binary, the base 2 number system. This particular joke involves the decimal (base 10) number system and the octal (base 8) number system.

If you can figure out binary, octal is not too much of a stretch. The octal number system uses eight digits: 0, 1, 2, 3, 4, 5, 6, and 7. Each place in a number represents a power of eight. So instead of the ones, tens, hundreds, thounsands, etc, you’ve got the ones, eights, sixty-fours, five hundred twelves, and so on. In the octal number system, the number 31 represents 3 eights and 1 one, or 25 in the decimal number system. Therefore, Dec 25 (or 25 in decimal) is the same as Oct 31 (31 in octal). As musician Tom Lehrer quipped, octal “is just like base 10…if you’re missing two fingers.”

Simple, right? So why would a computer scientist need to know about octal?

Computers think in binary, but octal is a bit easier to use. That’s because the same number can be represented in octal using a third as many digits. Computer scientists who enter data in octal are therefore one-third as likely to make a mistake, and if a mistake does occur, there are one-third as many digits you have to search for the error.

To be fair, hexadecimal (base 16) is even more convenient, but this joke isn’t about hexadecimal, so there.

Furthermore, since 8 is a power of 2 (the third power, to be exact), binary numbers convert easily to octal and vice versa. (10 isn’t a power of 2, so decimal-binary conversions are a bit more labor-intensive.) Let’s say you want to convert the binary number 10110101 into octal. First you would break the number into groups of three digits each, starting from the right, like this: 10 110 101. Then you would interpret each three-digit group into its equivalent one-digit value, each of which will be between 0 and 7.

  • 000 = 0
  • 001 = 1
  • 010 = 2
  • 011 = 3
  • 100 = 4
  • 101 = 5
  • 110 = 6
  • 111 = 7

So 10110101 in binary translates into 265 in octal, or 2 sixty-fours, 6 eights, and 5 ones. In decimal, that’s 181. Simple.


On The Stoicism of Helium

Helium walks into a bar. The bartender tells him “Sorry, we don’t serve noble gases here.” Helium doesn’t react.


Helium (symbol: He) is the second element – both in terms of atomic number and abundance in the universe. It sits at the top right corner of the periodic table.

Helium is the lightest member of the element family known as the noble gases. The noble gases also include neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and maybe element 118. The noble gases are unique among the elements in that they all have low melting and boiling temperatures (which explains why they are all gases at room temperature). Also, the noble gases are very unreactive; they do not tend to form compounds with other elements.

I could stop right now and you would understand the joke. Helium doesn’t react because it’s a noble gas, and noble gases don’t react. But there’s much more to tell, so please indulge me while I bore you to tears explain why noble gases are the way they are. This is your last chance to log off before you learn about electron configurations.


Still here? Good.

We’ve already discussed how the electrons in atoms are arranged into concentric shells (or energy levels) around the atomic nucleus. Actually, it’s a little more complicated than that. Each energy level can be further divided into sublevels. The sublevels are given odd names like sharp, principle, diffuse, and fundamental, but we’ll just call them s, p, d, and f.

The first energy level – that is, the one closest to the atomic nucleus – has only one sublevel. It’s an s-type sublevel, so it’s called 1s (read that as “one-S”). All s-type sublevels can hold 2 electrons, so the entire first energy level can hold 2 electrons.

In atomic physics there’s a guideline called the Aufbau principle. Aufbau is a German word meaning construction. It says that the electrons in atoms fall to the lowest-energy sublevel that is available. Once a sublevel is filled with electrons, the next highest sublevel begins to fill, and so on.

If an atom has one or two electrons, the 1s sublevel is perfectly capable of accommodating them. However, if an atom has 3 or more electrons, it must tap into higher-energy sublevels.

The second energy level is made of two sublevels. It also has an s-type sublevel (in fact, all energy levels contain an s-type sublevel) but it also contains a p-type sublevel. These two sublevels are called 2s and 2p (or not 2p? That is the question!)

Like the 1s sublevel, the 2s sublevel also holds 2 electrons. The 2p sublevel can hold 6 electrons. All told, the second energy level can hold up to 8 electrons.

And so it goes. As the electron population grows, so does the number of sublevels and energy levels. If you’re assigning homes to an atom’s electrons, you continue adding energy levels and sublevels until you run out of electrons. The last sublevel may or may not be full, but every sublevel prior to the last one must be full (except for a few special cases that we’re not going to discuss right now).

Sublevels

The sublevels don’t necessarily get filled in the order you might expect. 1s, 2s, 2p, 3s, and 3p fill with electrons in order, but the next sublevel to be filled after 3p is 4s, not 3d. The 3d sublevel fills after 4s, then comes 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, etc, etc. This arrangement may seem bizarre, but it plays a major role in determining if and how an atom will react with other atoms.

See, the most important electrons in any atom are the valence electrons. Valence electrons are the electrons that inhabit the highest energy level – the one farthest from the nucleus. Atoms that have one through seven valence electrons will generally react with other atoms, either by losing, gaining, or sharing electrons. Atoms that have eight valence electrons, however, are special…eight valence electrons is a very stable arrangement. Why? Because when an atom has eight valence electrons, its highest s-type and p-type sublevels are just filled. Let’s take a look at the arrangement of electrons in each of the noble gas atoms:

Helium (2): 1s2
Neon (10): 1s2 2s2 2p6
Argon (18): 1s2 2s2 2p6 3s2 3p6
Krypton (36): 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
Xenon (54): 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6
Radon (86): 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6

For each element, the number in parentheses tells you the total number of electrons. The raised numbers tell you the number of electrons in each sublevel. I’ve color-coded the sublevels to make it easier to see which electrons are grouped together in an energy level. Take a look at each of the noble gases (except for helium). Notice how they all have a total of 8 electrons in their outermost energy levels, distributed between the outermost s-type and p-type sublevels.

These arrangements are really stable. Because noble gases have full s– and p-type sublevels in their outermost energy levels, they tend not to gain, lose, or share electrons under normal conditions. That’s why we say that noble gases don’t react with other atoms.

Now of course the joke is about helium, and you’ve probably noticed that helium does not have 8 valence electrons; in fact, helium doesn’t have 8 electrons at all. Regardless, helium still has a complete 1s sublevel, which confers its own kind of stability. Chemically, helium reacts (or more appropriately, it doesn’t react) more like the noble gases than like any other family of elements, and so it is considered to be one of them.


Here are two other interesting tidbits about helium which won’t enhance your understanding or appreciation of the joke, but might give you something to think about.

  1. The name helium comes from the word Helios, who was a Sun god in Greek mythology. The element was so named because it was discovered first in the Sun, via an anomalous spectral signature in sunlight, 25 years before it was isolated on Earth.
  2. Despite helium’s abundance in the universe, we’re running out of it on Earth. The looming helium shortage has implications far beyond birthday party balloons.

Hamburger Humor

Q. Why does hamburger have less energy than steak?

A. It’s in the ground state.


English is kind of a funny language (not funny ha-ha…funny strange). When you say ground in reference to beef, you’re using the past participle of the word grind. Why is ground the past participle of grind? Who knows? It just is! Deal with it!

And then of course there’s the ground, that huge surface outside that pilots spend their careers avoiding. Interestingly (or maybe not), that ground has very little to do with grinding, etymologically speaking. Like I said: English = funny.

Because the ground has great fundamental importance to almost everything we humans do, the word ground has permeated many disciplines, including chemistry and physics. There, the word refers to the absolute lowest level of something. In atomic physics, the phrase ground state is the lowest energy configuration in which an atom’s electrons can exist. When an atom’s electrons are in their ground state, they have no capacity to give off energy.

So let me back up just a bit. The electrons of an atom are arranged into concentric shells, sort of like Russian nesting dolls except less creepy and a whole lot smaller. These shells are also known as energy levels. The closer a shell is to the nucleus, the less energy its electrons have. Electrons can move from shell to shell, but they must absorb and release the appropriate amount of energy as they do so.

The most desirable real estate in an atom – as far as electrons are concerned – is close to the nucleus. Just as water tends to flow downhill, the electrons in an atom will rush “downhill” to find a slot as close to the nucleus as they can. (Space is limited in each shell) In an atom with only one electron (hydrogen), the electron naturally tends to fall into the first shell. When this happens, the hydrogen atom is in its ground state.

If you zap the hydrogen atom with just the right amount of energy, the electron can be temporarily bumped into a higher energy level. In this case, we say that the hydrogen atom is excited. An excited atom is unstable; it soon allows its electron to pay back the bolt of energy (usually in the form of light) and fall back to the ground state. It’s kind of like a sugar crash, but with less crankiness.

One presumes that if you zap a slab of hamburger beef with a bolt of energy, the beef can be simultaneously ground and excited. What a state that would be!


Polar Pun

Q. Why did the bear dissolve in water?

A. It was a polar bear!


In chemistry, you can classify molecules as either polar or non-polar. Actually, most molecules fall along a spectrum between those two extremes, but let’s not pick nits. The classic example of a polar molecule is water. What makes water polar, and what does it mean for a molecule to be polar?

You may recall that water has the chemical formula H2O, which means that every water molecule is made of one oxygen atom bonded to two hydrogen atoms. For reasons we’re not going to get into right now, these three atoms don’t form a straight line; instead, a water molecule has a V shape, with the oxygen atom at the point of the V.

The oxygen and hydrogen atoms are held together by shared electrons, but they don’t share equally. See, oxygen is a bit of an electron hog. It pulls the shared electrons more strongly than the hydrogen atoms. Consequently, there’s a bigger electron presence around the oxygen atom than there is around the hydrogen atoms. The oxygen point of a water molecule develops a slightly negative charge, while the hydrogen tips develop a slightly positive charge.

Even water from the tropics is polar.

Even water from the tropics is polar.

So each water molecule is sort of like a tiny magnet, except it has a positive and negative pole instead of a north and south pole. We say that water molecules are polar because of this uneven distribution of electric charge.

Of course water isn’t the only polar molecule; lots of molecules have lopsided electron distributions. Other examples of polar substances are ethanol, ammonia, and acetic acid (found in vinegar).

Acetic acid, ammonia, and ethanol walk into a bar...

Acetic acid, ammonia, and ethanol walk into a bar…

A non-polar molecule generally doesn’t contain any electron-hogging atoms that pull electron density to one side of the molecule; instead, their electrons and charges are distributed evenly. Oil and grease are typical non-polar molecules.

There’s a useful (if a bit oversimplified) phrase used in chemistry to describe interactions between polar and non-polar molecules: like dissolves like. In other words, polar substances are likely to mix with other polar substances, and non-polar substances are likely to mix with other non-polar substances. Polar and non-polar substances, however, are generally not miscible.

That explains why water mixes so well with acetic acid, ammonia, ethanol, and other polar substances. It also explains why water does not mix with oil or grease, although oil and grease will mix with each other.

The problem is one of attraction. See, all molecules are attracted to each other, but polar molecules like water are more attracted to each other than they are to non-polar molecules. Oil molecules are attracted to water molecules, but water molecules will not separate from each other long enough to allow oil molecules to mix with them. Water molecules are stuck-up snobs*.

So if we had a bear that was polar in the chemical sense rather than in the geographical sense, it would be unwise for that bear to enter water. Presumably his various components would quickly and easily mix with the water, and our poor polar bear would be no more. Sad.


*Water molecules are actually incapable of emotions or social elitism. Please forgive my metaphor.