funding for this program was provided by... additional funding provided by the people of dow, the company that lets you do great things, the 8,000 scientists of the eastman kodak company, the exxon education foundation on behalf of exxon scientists, and... captioning made possible by the annenberg/cpb project i'd like to show you the most important piece of equipment you're likely to encounter in a chemical laboratory. how much will it cost? was it invented in the united states

and made in japan? let's see. this is it. not a superconducting supercollider, is it? not a piece of equipment that's worth $100 million. just a piece of paper, a chart, an idea, a tool for the mind. this was invented by mendeleev, a russian, 120 years ago. it's called the periodic table, and it's worth more to chemists than all of the pieces of equipment in our laboratories.

what are the properties of the substances in the world around us? there are two types of propertis. chemical properties refer to the element's ability to combine with other elements and form compounds. physical properties include density, hardness, melting point, boiling point, and conductivity. each element is different from every other eleme in its chemical and physical properties. this uniqueness can be traced to the element's atomic structure, but some groups of elements also share common properties that vary systematically and predictably. these common properties are the basis of the modern periodic table. there are 109 elements in it. 88 occur naturally. the other 21 are manmade,

or artificial, elements. for centuries, latin was the common language of science, so many elements have latin names. for instance, iron was ferrum, so its abbreviation became fe. gold was aurum, latin for "shining dawn," so it became au. madame curie discovered an element and named it after her native poland, "polonium," and more recently discovered elements have been named after famous people, such as einsteinium, named for albert einstein, and nobelium, named for the man who established the nobel prize, alfred nobel. besides a symbol for the element's name, in this case helium, each box also contains some important numbers. notice the number below the he symbol. this is the atomic mass of the element, the total mass of the protons and neutrons.

all helium nuclei contain two protons. however, the number of neutrons may vary. for example, there's a rare form of helium which has only one neutron in the nucleus. the two varieties of the same element are called isotopes. the atomic mass of an element is the weighted average of the masses of the isotopes in the naturally occurring element. the number over the symbol is the element's atomic number-- the number of protons in each nucleus. an atomic number is what determines an element's position in the table. the elements in the table are arranged in order of ascending atomic number as you go from left to right. here we have hydrogen, number 1, way over here, helium, number 2, then lithium, 3, beryllium, 4, boron, 5, and so on to neon, 10, back to sodium, 11, magnesium, 12,

and so on, left to right. now, there's another facet to the table. because of the way it's laid out, each element is a member of a group that goes up and down the table and a period that goes across the table. for example, potassium-- it is a member of this group, and it is a member of this period. there are seven horizontal periods running from left to right. each one has been assigned a number which is placed at the left of the period. 14 of the elements in periods 6 and 7 are laid out below. if they were placed in the table, it would look like this. it makes it easier to arrange the table if they are at the bottom. there are also 18 vertical columns called groups, or families. each group is designated by a number and a letter

which is placed at the top of the column. elements within a family all have similar properties. to demonstrate this, let's look at one family on the far right of the periodic table... these balloons contain the first five noble gases. we have helium, neon, argon, krypton, and xenon. now, we're missing radon because it's radioactive. we're all familiar with helium. it's used in balloons and blimps. the rest are used to fill various light bulbs and lamps. but what are some of the properties that they have in common? they're odorless, and they're colorless, and they're all quite unreactive. as you go down in the family, each one gets heavier than the previous one. let me show you what i mean. this is helium.

there it goes. this is neon. it's somewhat lighter than air. there it goes. now, argon and krypton are both heavier than air. and xenon is the heaviest of the ones we've seen. it's the proverbial lead balloon. you can begin to see the different types of information derived from the periodic table. but how do chemists use the table in their work? glassmaking is one example. at one time in the ancient world, glass was so rare that it was prized more highly than jewels or gold. as we mastered the techniques of glassworking, glass became a commonplace necessity. the types of glass multiplied tremendously so that today glass comes in many forms and colors.

artists use it to create new and intriguing constructions. craftsmen mold it by hand into the elegant forms of steuben crystal, and factories manufacture glass for countless everyday uses. basically, different types of glass are made by mixing silicon dioxide, sand, with different metal oxides, then melting them together. the choice of oxides, which determines the characteristics of the glass, is guided by the periodic table. dr. gerry fine is a glass chemist at the corning glass works in corning, new york. i cannot imagine working without the periodic table because scientists are interested in looking for systematic relationships between different substances and different elements. the periodic table is a simple way of looking up and finding systematic relationships between different elements that we can understand at a simple level. in the glass research center at corning,

thousands of samples are poured yearly as new types of glass are developed and perfected. one group of elements frequently used to make glass is on the far left of the periodic table... by mixing in different alkali metals, glass with different characteristics can be produced, so understanding their variations in behavior is important to glassmakers, and, indeed, to all chemists. we call this family the alkali metals. they make up group 1 in the periodic table. the first element is lithium, and then there's sodium and potassium. down here is rubidium, and this one is cesium. now, do you notice anything that they all have in common? you probably see that they're all stored in very unusual ways,

and we do this because they're all highly reactive. i have here three containers of just water, and i'm going to take a piece of this lithium and put it into the water. now, watch what happens... how it starts to fizz a little bit. the fizzing is the reaction of lithium with the water to produce hydrogen gas. let's try the sodium. i'll get a small piece of that, not too big, because we don't want the reaction to be too violent. oh, that reacts much faster, doesn't it? see the sodium bouncing around there, again fizzing, giving off that hydrogen gas. ok, let's try potassium, the most reactive of the three. i'll get a small piece of that and put it into the water.

wow! that really reacted violently. did you see the immediate reaction of the potassium? again, it formed that hydrogen gas, and the hydrogen gas was ignited. so the alkali metals all have similar chemical properties, but they also vary systematically. as you go from the top to the bottom of the column, the atoms of each element become larger. chemists can use this characteristic to increase the strength of their glass. the size of an atom increases as we go down any column. in the alkali metal group, the atomic size increases from lithium to sodium to potassium, and so on. as we move across a period, starting with an alkali metal, atom size gets smaller until we get to a new period. here we see a jump in atomic size in the next alkali metal and a decrease along the period.

this pattern repeats itself throughout the table and is called periodicity. everyone is aware that glass tends to be a brittle material. if you've thrown a baseball through a window, you know that glass breaks quite readily. however, there are ways of taking simple window glass, which is made of sodium, calcium, and silicon, and treating the glass to make it strong. one way that we do that is by use of the periodic table. if we take that glass that contains sodium and substitute potassium in the surface for the sodium or substitute an element that behaves basically in the same way, but is slightly larger, we can enhance the strength of that glass and make strong glass. the results of this process are easily demonstrated. if a steel ball bearing is dropped from 1 foot onto glass made with the alkali metal sodium,

watch what happens. the sodium-based glass shatters completely. watch what happens if the same ball bearing is dropped on glass where potassium was substituted for sodium. the ball will be dropped from 20 feet. the way we do that is by taking the glass which contains sodium and dipping it in a bath containing molten potassium. the molten potassium substitutes for the sodium in the glass on the surface of the glass. because, from the periodic table, we can tell that potassium is larger than sodium, the potassium literally stuffs the surface of that glass. the predictive ability of the periodic table was first demonstrated by a russian chemist, dmitri mendeleev. 100 years ago, he developed the predecessor of our modern table. mendeleev's table included all the elements then known

and was consistent with their varying properties. for three undiscovered elements, he left blank spaces, predicting that they did exist and that their properties would be consistent with their position in the table. for his time, it was an amazing hypothesis. one position that he left blank was this position for gallium. based on the properties of the two neighboring elements, aluminum and indium, mendeleev was able to predict some of the properties of gallium. he was also able to predict two other elements, germanium and scandium. when the elements were discovered and their properties measured, mendeleev's predictions were found to be remarkably accurate. in this century, another chemist, an american, rearranged the structure of the table based on the properties of elements that he had discovered. his name is glenn seaborg. in 1944, the periodic table didn't look like it does today.

the periods and groups were laid out differently. back in the days of mendeleev, and actually extending into the 1930s, the heaviest elements, thorium, protactinium, and uranium were put into the periodic table up in the body of the periodic table under hafnium and tantalum and tungsten, and it was my idea in 1944, while i was working on the... at the metallurgical laboratory in chicago on the manhattan atomic bomb project, that these might be misplaced and that they might be the first three members of the actinide series. and then i boldly and against the advice of some of my eminent inorganic chemist friends, plucked those out of the body of the periodic table

and put them in the row below and then continued that with 93, 94, and so forth, up to 103. the idea to rearrange the table occurred to seaborg one friday afternoon. he was drafting a classified report for a seminar on monday. he decided to include this idea in his report. i presented this at that monday seminar, and it went over like a lead balloon. the idea that one would be brash enough to change the periodic table after all these years, in this fashion, when everybody felt that thorium, protactinium, and uranium should be in those sacrosanct positions up in the body of the periodic table under hafnium, tantalum, and tungsten. his discoveries of the new elements remained classified until after world war ii. when he was able to publish, he incorporated his new arrangement of the periodic table.

i showed this periodic table to some of my friends, the most eminent inorganic chemists in the world, and told them that i planned to publish it, and they said, "don't do it, glenn. it's wrong. it will ruin your scientifireputation." well, i'm fond of saying that i had an advantage. i didn't have any scientific reputation at that time, so i published it. seaborg's new arrangement enabled him to predict the properties of still more elements. his ideas were later verified when the elements were produced artificially. seaborg was awarded the nobel prize in chemistry in 1951. his rearrangement is our modern periodic table. what ultimately determines the position of an element in this modern table is the way the electrons are arranged in the energy levels of the atom. as we move through the table and the number of electrons in an atom increases,

the energy level diagrams contain more and more levels and sublevels. both the number and types of electron clouds increase in complexity. this is the energy level diagram for hydrogen's one electron in an s-cloud called the 1s. lithium's three electrons are diagramed like this-- two electrons in the 1s cloud. each cloud can contain two electrons. then the third electron is in another cloud, an s-cloud at the second level. let's move forward to sodium and look at an energy diagram for its 11 electrons. its first two electrons are in the cloud at the 1s level. its next two electrons are in an s-cloud at the second level. this is actually only the first of two sublevels at the second level, so it's called the 2s sublevel. the next six electrons of sodium

are in the other sublevel, called the 2p sublevel. notice the number of clouds in the 2p sublevel. there are three p-shaped clouds in it. each of these clouds contains two electrons. where does sodium's 11th electron go? as we move higher on this energy diagram, we encounter the first sublevel of level 3, the 3s. it has only one s-orbital in it. sodium's 11th electron goes here. when chemists diagram energy levels of electrons within an atom, they replace the figures of the clouds with blank lines. arws are used to indicate the presence of electrons in each orbital. this is the diagram for sodium's 11 electrons. sodium is the second alkali metal. it has one electron in its outer orbital, the 3s.

this is the diagram for lithium, the first alkali metal. see its highest energy level? it is only half-filled with only one electron in the 2s sublevel. the similarities and properties of lithium and sodium-- and, indeed, all the alkali metals-- are due to the similarities in their outer electron structure. the outer electrons in any atom are called its valence electrons. the noble gases are another example of a similarity in outer electron structure. they have a filled s or p sublevel, a very stable arrangement. next to them is an important group called the halogens. they are all missing an electron from an almost-filled sublevel, which makes them very reactive. now, as the number of electrons in an atom increases, what are the rules these electrons follow in filling different sublevels and orbitals?

to find out, don showalter went to st. albans school on the grounds of the national cathedral in washington, d.c. we will show you how the electrons fill up the various energy levels that you saw on that diagram. to help us, we have 11 baseball players. right, coach! these baseball players will now represent electrons. we will have an electron practice. they're going to practice the rules that chemists use to fill the energy levels. here's the ground rules. these bleachers represent the various energy levels, the lowest one being the 1s, colored blue. the next energy level is the 2s. it's colored green. all right. now the 2p has 3 sublevels, and it's colored red. 2p with 3 sublevels! good! the highest energy level is the 3s,

and it's colored yellow. all right. now, there are three basic rules that we have to follow. rule number one--electrons fill lowest energy level first. ok. here's rule number two. no more than two electrons in any one orbital. beautiful! here's rule three. if there's more than one orbital in a sublevel... one electron in each orbital before you double up. you got it? yes, coach! let's get energized! the first element is hydrogen. go! hydrogen has one electron, so it goes in the lowest energy level available, the 1s. now we're going to skip to nitrogen.

go! nitrogen has seven electrons. the first 4 fill up the 1s and the 2s. what about the next three? one goes in each of the 3 2p orbitals. now we'll skip ahead to sodium. you ready, team? yes, coach! sodium has 11 electrons. the first 4 go into the 1s and the 2s. the next three go into the two p orbitals. then numbers 8, 9, and 10 go in. finally, the 11th electron goes into the 3s sublevel. that's how electrons fill energy levels. right, team? right, coach! scientists at the smithsonian museum have applied a technique that uses information about the energy levels of different atoms to study works of art. this technique analyzes the elements in different pigments and is called x-ray fluorescence. jacqueline olin is a chemist at the smithsonian.

if, for example, you were to know an artist's work so well that you knew that artist neveused a particular pigment in all the paintings that have been studied, and there's a painting in question, one might analyze a painting to determine whether a pigment that isn't characteristic of that artist is present. x-ray fluorescence involves bombarding the atoms in the painting with x-rays, causing them to eject an electron. to see exactly how this happens, let's return to the electron team. here are the electrons in their energy levels for the element sodium. as an x-ray enters the atom, it knocks out an electron in the lowest orbital, the 1s. when this happens, some of the electrons in higher energy levels fall to lower energy levels, filling the gaps. as the electrons cascade down to lower energy levels,

they give off an x-ray pattern that is characteristic of each element. instruments analyze these x-rays and identify what element is present. it's very nice to be able to quickly determine what elements are in the painting because we've looked at the painting in terms of the colors we see, and we want to know if that blue is a copper-containing blue. that can be done readily using x-ray fluorescence to identify the elements present in that area, so it's a nice technique for nondestructively and quickly identifying some elements present in the painting. to review... the elements in the periodic table are arranged in serial order according to their atomic number. the rows are called periods, and the columns are called groups.

the size of the atoms increases as we go down in a group and decreases as we go across any period. this is an example of a periodic property. elements in any group have similar arrangements of electrons in their energy levels. therefore, they have similar chemical properties. you can see right away that a given electronic configuration implies similar properties. for instance, the alkali metals, with their one electron in the s subshell, they all readily give up that electron, and no more than one electron. and all of the halogens, on the other side of the periodic table, with their missing electron in the p subshell, readily accept such an electron. one might ask, why do we concentrate on the outermost electrons and not all the other ones? it's because the outermost electrons are at highest energy.

they're furthest away from the nucleus. in them is chemistry. captioning performed by the national captioning institute, inc. captions copyright 1989 educational film center and the university of maryland

funding for this program was provided by... additional funding provided by the people of dow, the company that lets you do great things, the 8,000 scientists of the eastman kodak company, the exxon education foundation on behalf of exxon scientists, and... for information on this college telecourse, videocassettes, off-air videotaping, and books based on this series, telephone the annenberg/cpb project at...

funding for this program was provided by... additional funding provided by the people of dow, the company that lets you do great things, the 8,000 scientists of the eastman kodak company, the exxon education foundation on behalf of exxon scientists, and... captioning made possible by the annenberg/cpb project our world is filled with a variety of things-- plants, animals, the sea and air, rocks and minerals. everything is made of atoms so small they're invisible.

combinations of atoms form these larger varied objects. energy is certainly involved in bonding atoms, but how? if there is an interatomic glue holding our world together, what's the nature of that glue? intriguing and important questions, because nearly all the substances around us and within us are held together by chemical bonds. everything is made of atoms, but the building blocks of this world

are groups of atoms-- big or small in number, connected up to each other. in this flask of water there are 10 to the 24th or so water molecules. every one of them h2o. in every one, an oxygen connected up to two hydrogens. in this salt, there is a vast, ordered array of sodium and chloride ions. we've got to figure out what holds atoms together in salt or in water. the key to chemical bonding is this marvelous periodic table of the elemets and a knowledge of the electron configurations of the atoms. in particular, those of the noble gases, like helium or neon. the noble gases are chemically inert. why? because they have a filled s and p electron cloud. now, with very few exceptions,

there are no compounds of the noble gases, but everything else in the periodic table-- arsenic, copper, indium, nitrogen, sulfur, nickel-- these do form compounds by trying to achieve the stable electron configuration of the noble gases. there are at least two ways to do that. the elements in compounds are held together primarily by ionic or covalent bonds. the basic rules governing how these bond form are-- first... atoms lose, gain, or share electrons to complete their valence shells, and second... electrons tend to exist in pairs. only the six noble gases do not readily combine with other elements because their valnce shells are already full.

making and breaking these chemical bonds is chemical change. when chemical change occurs, energy is involved. it might take a lightning bolt or something as complicated as algae to break a chemical bond. what exactly are these bonds, and how do they form? electrostatic attraction of oppositely charged particles--ions-- forms one type of bond, called ionic bonding. how do ions form? let's look at an alkali metal, sodium. a sodium atom has one valence electron. its energy level diagram looks like this. very little energy is required to lose that electron. the outer shell is now full. a positive sodium ion has been formed, smaller than the atom. on the other side of the table,

a chlorine atom has seven valence electrons. energy is given off when it gains an electron, filling its valence shell, forming a negative chloride ion. when sodium and chlorine are brought together, one gives off an electron, the other accepts an electron. they produce an ionic crystalline solid--salt. energy is involved, as demonstrator don showalter explains. what would happen if we mixed together sodium that wants to lose an electron with chlorine that wants to acquire an electron? let's see. in this beaker is chlorine gas. see the green color? that's a poisonous gas. what i want to do is to heat a piece of sodium metal. i'm going to put a piece into this glass spoon. i'm going to melt it a little bit, get it in the bottom there.

get it nice and molten, and put it inside, and let's see what happens. that's quite a reaction, huh? a lot of light. it gets more and more intense. there's a white powder that's forming in there. certainly the reaction is giving off a lot of energy. once it calms down, let's see what it forms. there's a white crystalline material that has formed on the side of the beaker. that's sodium chloride, regular table salt. what we have done is to take two elements that are quite dangerous and combine them into a substance

that is essential for life. sodium chloride, table salt, is a member of a huge family of salts, all crystalline solids. the electrostatic forces between the oppositely charged ions holds them together in the crystal. the electrical charge is evenly distributed over each ion, so ions of opposite charges are attracted from all directions. in sodium chloride, each chloride ion is surrounded by, and holds, six sodium ions. each sodium ion is surrounded by, and holds, six chloride ions. this results in a rigid, ordered pattern of alternating positive and negative ions. nacl is the formula of sodium chloride. it implies there is one ion of sodium for each chloride ion. that one-to-one ratio of the ions

exists throughout the cubic crystal. dr. jeffrey post, a crystallographer for the smithsonian institution, studies mineral crystals, like salt. if you took a magnifying glass and looked at the salt crystals from your saltshaker at home, you'd see that each of those crystals looks like this crystal on a smaller scale. under an electron microscope, magnified hundreds of thousands of times, the crystal shapes are exactly the same, the same cubic shape. that's an inherent property of he structure. the lattice structure formed by the ions give sodium chloride and other salts distinct properties unique to ionic compounds. i have two crucibles. both contain white, crystalline solids. they look much the same. however... one of them is ionically bonded. if the way substances are bonded together

give them different properties, we ought to be able to test that. one way is to see if they conduct electricity. we can do that by using this setup-- light bulb and electrode system. let's turn on the electricity and... nothing happens. well, sure, nothing's going to happen. the circuit's open. see what happens if i close it with this screwdriver? see, the light comes on. how about this one? all right. instead of using that screwdriver, what if we would lower the electrodes into the substances, test the conductivity that way? lower them, and look what happens. nothing. the light bulbs do not light up. if one of them is ionically bonded, maybe in the solid, the ions can't move around. what if we could help it by melting it? oh, i hear something happening.

oh, look. it's getting a little brown. i see some liquid coming around there. i've got all liquid, and this does not conduct electricity. so in the molten form, this is a nonconductor, nonelectrolyte. let's see what's happening over at the other crucible. i'm heating this one. i have to heat it really hot, looks like, in order for anything to happen. oop. there we go. here we go. the light bulb is lighting. the bulb is lit. it must mean now that as we melt this substance,

it conducts electricity. so what we see is that this substance in this crucible is an electrolyte. the substance over here is a nonelectrolyte. it doesn't conduct electricity. let's do one more test. i have two beakers here, each with a pair of electrodes in them. i'm going to put in there some pure, distilled water. water into this one... and water into this one. ok. now let me turn on the electricity with these switches. let's see what happens. nothing. pure water does not conduct electricity. now, into this beaker let's put some of this white solid number one.

look what happens. the light comes on. when solid number one dissolves in water, it conducts electricity. it is an electrolyte. let's try white solid number two. looks pretty much the same. put it in there. nothing happens. maybe a little more. nothing. solid number two does not conduct electricity. it is a nonelectrolyte. what do you think these two solids are? well, solid number one was ordinary table salt, sodium chloride. and solid number two is ordinary sugar. salt and human history are closely linked. ancient people understood its value to life itself. salt was once as valuable as gold.

good people are still "the salt of the earth." today, we produce 40 million tons of sodium chloride a year, half of it coming from caverns like this one beneath the louisiana delta. the rest of our supply comes from huge evaporating ponds or from salt wells. very little of this salt actually reaches the table. simple salt is needed by the chemical industry. chlorine, sodium hydroxide, or lye, and sodium carbonate are all made from sodium chloride. and salt is needed by most living things. cows seek salt instinctively. whole herds can be moved by simply moving the salt lick. in mammals, salts are practically all dissolved into solutions of ions in bodily fluids. the concentration of the proper ions

must be maintained because that concentration actually affects the cell membranes. other common salts are calcium chloride, which is spread on streets to melt ice... and stannous flouride, the salt of tin and fluorine used in toothpaste. these different salts might have different crystalline structures. the ion ratios and sizes may be different. this is a calcite crystal. the edges come together at an angle. they're not perfectly squared off like in the salt or in the halite. this is a property of calcium carbonate. the calcium ions and the carbonate ions stack together and repeat in three dimensions millions of times to build up a crystal. because of the different shape and charges of the carbonate molecules and the calcium ions, these stack together in a different manner.

the result is a crystal shape quite different from the halite. this table salt is our most commonly known ionic compound, but ionic bonding is not the only way that atoms can combine. most substances around us are molecules held together in another way. take this salad oil or vinegar or any molecule in my body. the atoms in these molecules are held together in a different way, by covalent bonding. covalent bonding is the most common type of chemical bonding that holds atoms together in molecules. molecules are electrically neutral combinations of different atoms. unlike ionic substances, which are solids, molecular substances can be solids, liquids, or gases.

to understand covalent bonding, let's begin with the simplest element-- hydrogen. imagine two hydrogen atoms, each with one proton in the nucleus and one electron. both atoms have the same energy, and their valence shells are not complete. as they move towards one another, the electron clouds begin to overlap. they start sharing electrons. a molecule is forming. when the clouds overlap, the electrons are paired together, shared. the valence shells are complete, and a covalent bond has been formed. on the sun, at high temperatures, hydrogen can exist as separate atoms. but at far lower temperatures here on earth, hydrogen exists as molecules which have lower energy than the two single atoms. here, that's the preferred natural state.

so, as the two atoms move together, the electron clouds begin to overlap, forming the molecule h2. the energy within this two-atom system decreases. whenever a covalent bond is formed, energy is released. where does the energy go? it's released to the surroundings. if controlled, that energy can move mountains. in certain compounds, chemical bonds are weak and can be easily broken, freeing the atoms to reform into stronger molecules. when they do, an enormous amount of energy is released. most conventional explosives contain nitrogen atoms weakly bonded to other atoms. why nitrogen? when nitrogen forms its molecule--n2-- the atoms will share three pairs of electrons. the bond formed is one of the strongest known,

and the energy released in the process makes nitrogen-based explosives unique, as don showalter will demonstrate. we've seen a little bit about nitrogen bonds. two nitrogen atoms will combine to form a stable n2 molecule. iodine, a member of the halogens family, will also form a stable, diatomic molecule. now, you would think the electrons in the nitrogen atom would be easily shared with three iodines, and you're right. this brownish pile you see in front of you is nitrogen tri-iodide, nitrogen bonded to three iodine atoms. nitrogen doesn't need much encouragement to go back to its elemental form--n2. when it does that, many times, the energy release is quite surprising. let me show you. i'm going to protect my ears with cotton. i'm going to initiate this reaction...

by the touch of a feather. let's watch. wow! what a reaction, huh? the nitrogen tri-iodide went to nitrogen--n2 and iodine--i2. you saw the purple iodine cloud that came out of there. now, this strong tendency of nitrogen to form that n2 bond has many applications. explosives have impacted civilization in peace and in war. tunnels, canals, excavations, and roadbeds were all made possible by these high-energy explosives. the trinitroglycerin of dynamite and tnt made mining more efficient, but the explosive of choice in today's blasting industry is a fertilizer. the white stuff that's going in there

is a base load of ammonium nitrate and fuel oil. ammonium nitrate, another nitrogen compound, is a fertilizer farmers use on their fields. these holes will go off in a timed sequence. linn coursen is a research fellow at eti, the company supplying the explosives for today's shoot. what will happen is that the charges in front will begin moving the rock out of the way, so that the charges in back will not have as much rock to move out. each hole is filled with the ammonium nitrate fuel oil mixture and a primer of tnt. in a fraction of a second, there will be millions of chemical bonds breaking and reforming to produce an explosion.

4 1/2 tons of ammonium nitrate were used in blasting away this rock cliff. when any covalent bond forms, energy is released. the same amount of energy is needed in order to break that bond. this is something nature does every day. there is nitrogen in all living things. muscle, hair, and dna all contain nitrogen bonded to other elements. but 80% of the atmosphere is nitrogen molecules held together by strong triple bonds. how do living things get the form of nitrogen they need? lightning helps. it has enough energy to break apart nitrogen molecules, which then react with oxygen in the air, eventually forming nitric acid. this natural acid dissolves in rain

and falls to earth as a dilute solution. there, it is absorbed and metabolized by plants. some plants, though, convert molecular nitrogen differently. soybeans and other legumes, like peas and peanuts, host a unique bacterium in their roots. this bacterium converts the nitrogen molecule into a nitrogen compound, ammonia, which the plant can then use to make amino acids. exactly how the bacterium works is the subject of vigorous research. from the u.s. department of agriculture, don keister. this is one of the very unique enzymes in all of nature, because it is the only... it is the only solution nature has come up with for biologically reducing nitrogen. the soybean and the bacterium have a symbiotic relationship. the plant houses and feeds the bacterium,

and, in turn, it receives the nitrogen it needs. but not all plants can host these nitrogen-fixers. they have to rely on rain and manufactured fertilizers, like ammonium nitrate, and they're expensive. as the world's population grows, so does the demand for food, which depends on nitrogen fixation. we are currently using something like 300 million barrels of oil per year in this country alone to produce nitrogen fertilizers. we must double the food supply over the next 20 years. where is that energy going to come from? where is the fertilizer going to come from? for feeding the world, there are two basic options-- we can produce more fertilizer, at greater cost and some risk to the environment, or we can create new varieties of nitrogen-fixing plants. both options are being pursued worldwide.

to review... except for the noble gases, like helium and neon, which have full valence shells, everything around us is chemically bonded. ionic and covalent bonding are the two main ways which elements can bond. ionic bonds form when atoms either give up or acquire electrons. in the process, they become positive or negative ions, which attract one another, producing salt crystals. covalent bonds are formed when two or more atoms complete their valence shells by sharing electrons. as atoms form molecules, energy is released, so molecules have less energy than the initial atoms. to break molecules apart, back into their constituent atoms, energy must be

put back into the system. my own research actually has to do with bonding in molecules. what i want to know is why a molecule has the structure that it does. let me tell you a story, something i did a few years ago. there's an important class of molecules called organometallics. they have an organic piece and a metal atom. a german group made a new one of these, tris-ethylene nickel. it has in it ethylenes and a nickel atom. when they made it, they didn't know its shape, its structure, whether the ethylenes were standing up, like soldiers, or if they should be lying down, the way they are in this model. why does it matter? well, the shape of a molecule is important in defining its properties.

molecules close to this one were active as catalysts in making polyethylene, but that's not the reason why i was interested in them. i just wanted to know their geometry. together with my coworkers, and looking at the way the electrons move in this molecule, we were able to predict that the ethylenes should be lying down, the way they are now. within a very short period of time, a group in england confirmed this prediction on a related platinum-containing molecule. you can see this is a problem in molecular architecture. chemical bonds are connections between atoms, of a definite strength, a definite length. they make molecules out of atoms, but knowing the bonding in a molecule is not sufficient. molecules also haver a characteristic shape, a structure, an architecture, which we will see in the next program.

captioning performed by the national captioning institute, inc. captions copyright 1989 educational film center and the university of maryland

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