Go to Gases

The work of Lavoisier prompted other scientist to develop a more quantitative approach to science and use accurate measurements for all their work. The result of this was a rapid development in the chemical understanding.

The first of these was the work of German chemist Jeremias Benjamin Richter (1762 - 1807) who turned his interests to acid - base neutralization reactions. In these experiments, he measured exactly how much acid was required to neutralize a given amount of base, and vice versa. What he found was that fixed and definite amounts of each were required. He published this idea of "equivalent weight" in 1792. The idea was quickly taken up by two French chemists who logically asked "does this sort of definiteness exist only in acid-base neutralization but throughout chemistry" Simply put they wanted to know whether a particular compound was made up of elements combined in the same fixed proportions independent of their origin or did the method of preparation of a give compound determine the ratio of the elements. One of the scientist, Berthollet's believed it was the latter but Joseph Louis Proust (1754 - 1826), who fled to Spain to avoid the revolution believed Berthollet was wrong and that the elements did combine in fixed and definite proportions, independent of the method of preparation. In 1799, he showed that Copper carbonate contained definite proportions by weight of copper, carbon and oxygen, no matter how it was obtained. He went on to show this was true for many many other compounds. This is the "Law of definite proportion", sometimes but known as "Proust's Law".

It was the English Chemist and school teacher, John Dalton (1766 - 1844) who looked at many of these earlier ideas and prompted by his own discovery that two elements could combine in different proportions under different conditions, but the resulting compounds were different. What he found was that if he mixed 3 parts carbon and 8 parts oxygen by weight he would exactly form carbon dioxide. If he mixed 3 parts carbon with 4 parts oxygen he made carbon monoxide. He quickly noticed that the combinations were all in the form of small whole numbers. This is the "Law of multiple proportions". But he didn't stop there. In 1803, Dalton advanced his idea further. since he felt the law of multiple proportions clearly fitted that atomistic notions of earlier scientists. He theorized that if oxygen was 1-1/3 times heavier than carbon and carbon monoxide contains one carbon and one oxygen then the compound would contain 3 parts carbon and 4 parts oxygen by weight. His next logical step was to theorize that if carbon dioxide contained one atom of carbon and to atoms of oxygen it should have a 3 to 8 ration by weight, which it did. He published this work in greater detail in 1808, entitled " A New System of Chemical Philosophy" . The idea was quickly verified by English Chemist, William Hyde Wollaston (1766 - 1828) giving Dalton's work much needed credibility and general acceptance.

In the 1740's, Benjamin Franklin (1706 - 90), who was the first great American Scientist as well as Statesman began looking at the ideas of Electricity. He believed that if a substance gained more than its share of electricity it would exhibit this by showing one kind of electric charge and that if it had less than its share of electricity, it would show a different kind of electric charge. He based these ides on the work of French chemist Charles François de Cisternay du Fay (1698 - 1739) who discovered in 1733 that there were two kinds of charge. One that could be put onto glass ("Vitreous electricity") and one that could be put-on amber ("Resinous electricity") and that one attracted the other.

Franklin guessed that the glass contained greater than the normal quantity of charge and so, said it contained a "Positive" amount of "charge". The resin however contained less than the normal amount of charge and so, said it contained a "Negative" amount of "Charge". These were simplified to "Positive Charge" and "Negative Charge" and have been used ever since.

By 1800, Italian physicist Alessandro Volta (1745 - 1827) had found a way of connecting two metals together and separating them with a solution through which this "new" charge could pass. He found that the system could be arranged so that the new charge charge was created as fast as the old charge was carried off along a conducting wire. This was to be the first electric battery and the first production of electric current. It was clear from now on that chemical reactions were related in some way to electricity, but it would be another century before this mystery was resolved.

Within six weeks of Volta's first description, the English Chemists, William Nicholson (1753 - 1815) and Anthony Carlisle (1768 - 1840) had theorized and shown that not only did chemical reactions produce electricity but you could use electricity to produce chemical reactions. By passing electricity through water, they produced bubbles at the metal strips. The gas at one strip was hydrogen and at the other, oxygen. This was the first decomposition of water into hydrogen and oxygen, a process that came to be known as electrolysis. What they found interesting was that when captured, the volume of hydrogen gas was exactly twice that of oxygen gas. This corrected Dalton's assumption that one atom of oxygen and one of hydrogen combined to form water but confirmed that the weight ratio was still 8 to 1. It followed then that if hydrogen weighed 1 then oxygen must weigh 16 since there was twice as many atoms of hydrogen as there were oxygen.


Volta's Battery

French chemist, Joseph louis Gay-Lussac (1778 - 1850), expanded this work and in 1808 announced the "Law of combining volumes" In this he said that when gases combined, they did so in small whole number ratios. This opened the floodgate to challenges of Dalton's one-to-one atomic ratios and soon it was clear that ammonia contained one nitrogen and three hydrogen and therefore the atomic weight of nitrogen was not 5 but 14. It was the Italian Chemist Amedeo Avogadro (1776 - 1856) who in 1811 recognized that if when equal volumes of gases combined then there must be equal numbers of atoms combining to form equal numbers of molecules. The problems was that when one volume of hydrogen was combined with one volume of chlorine, two volumes of hydrogen chloride would be formed. How could this be if hydrogen was one atom and chlorine was two atoms. The answer lay in the proposition that may be hydrogen and chlorine were actually composed of two atoms of each. Then 1 molecule of hydrogen (2 atoms) and one molecule of chlorine (2 atoms) would form two molecules of hydrogen chloride (each with 2 atoms). this is known as Avogadro's hypothesis.

By the 1860's, it was generally accepted that atomic weights were not whole numbers but generally non-integral. Following the work of American chemist Theodore William Richards (1868 - 1928), these were determined more accurately than ever before, an accuracy that represents the ultimate for purely chemical methods. This mean that chemists now needed a standard. The current use of hydrogen as 1 gave oxygen a value of 15.9 and since oxygen was so often used, this number was deemed inconvenient and changed to 16.0000. this gave hydrogen a value of 1.008. this standard remained until the mid 20th century.

It was the combination of Dalton's and Swedish Chemist Jöns Jakob Berzelius efforts that began to draw together the chemical symbolism. First Dalton used circles with dots and crosses, but realizing he would run out of suitable symbols, turned to circles with the first letter of the element in. Berzelius removed the circles, leaving us with the symbols used today, the first letter of the name of the element, most of which were originally in Latin. Whenever 2 or more elements used the same first letter then the second letter of the name was added to it. this made it very easy to start writing chemical names such as H2O and chemical equations such as
2H2 + O2 ---> 2H2O which came to be known as balanced equations because the number of atoms on each side were balanced.

It was left to the English Chemist Humphrey Davy to use the power of electricity to decompose molten compounds into their elements and in doing so was able to isolate, potassium (from potash), sodium (from soda), magnesium (from magnesia), strontium (from strontia), barium (from baryta) and calcium (from lime. Calcium is Latin for lime). In addition to these, a green gas, originally thought to be an oxide was found to be an element. Davy named it chlorine after the Greek word for "Green". Davy's student, Michael Faraday (1791 - 1867) actually contributed more to science than his teacher did. Faraday was an electrochemist of extraordinary talent. Faraday coined the names electrolysis and electrolyte. He named the metal strips, electrodes; the strips carrying positive charge were names anodes and those carrying negative charge, cathodes. He said the electric current was carried through the solution by entities called "ions" from the Greek word meaning "Wanderer" and that those "ions" traveling to the anode were anions and those to the cathode were cations.

1n 1832, Faraday announced the "First Law of Electrolysis" which stated that the mass of substance liberated at an electrode during electrolysis is proportional to the quantity of electricity driven through the solution. His "Second Law of Electrolysis" was that the weight of metal liberated by a given quantity of electricity is proportional to the equivalent weight of the metal. What this means is that if 2.7 times as much silver as potassium will combine with a fixed quantity of oxygen, then 2.7 times as much silver as potassium will be deposited from the compound by a given quantity of electricity.

This idea prompted other scientists to think that there were actually "atoms of electricity" since it had to be divided into minimum units to have this effect. It became common to say that "one atom of electricity was required to handle one atom of matter" and so on. Faraday was never happy with this idea and it was not until the end of the 19th century that the "atoms of electricity" were identified as electrons.

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Designed & maintained by Paul Charlesworth, Chemistry Department, Michigan Tech. April 07, 1999.