Mar 062018
 

On this date in1869 Dmitri Mendeleev presented his first periodic table to the Russian Chemical Society. There were previous periodic tables and Mendeleev’s publication almost coincided with German chemist Julius Lothar Meyer’s table. They both constructed their tables by listing the elements in rows or columns in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat. This ordering of the elements was a significant breakthrough in the evolving understanding of the structure of elements, and is still the basis for the periodic table in use today. In modern terms, the rows represent the electron shells, and the columns represent the number of electrons in the outer shell starting with one in the column of the left and ending with a full shell in the column on the right. On the far left the elements are highly reactive, on the far right they are virtually unreactive. Thus, in the first row, Hydrogen, on the left, is very reactive and Helium, far right, is inert. That’s why you fill a balloon, or zeppelin, with Helium and not Hydrogen.

In 1789, Antoine Lavoisier published a list of 33 chemical elements, grouping them into gases, metals, nonmetals, and earths. Chemists spent the following century searching for a more precise classification scheme. In 1829, Johann Wolfgang Döbereiner observed that many of the elements could be grouped into triads based on their chemical properties. Lithium, sodium, and potassium, for example, were grouped together in a triad as soft, reactive metals. Döbereiner also observed that, when arranged by atomic weight, the second member of each triad was roughly the average of the first and the third; this became known as the Law of Triads.

German chemist Leopold Gmelin worked with this system, and by 1843 he had identified ten triads, three groups of four, and one group of five. Jean-Baptiste Dumas published work in 1857 describing relationships between various groups of metals. Although various chemists were able to identify relationships between small groups of elements, they had yet to build one scheme that encompassed them all.

In 1857, German chemist August Kekulé observed that carbon often has four other atoms bonded to it. Methane, for example, has one carbon atom and four hydrogen atoms. This concept eventually became known as valency; different elements bond with different numbers of atoms.

In 1862, Alexandre-Emile Béguyer de Chancourtois, a French geologist, published an early form of periodic table, which he called the telluric helix or screw. He was the first person to notice the periodicity of the elements. With the elements arranged in a spiral on a cylinder by order of increasing atomic weight, de Chancourtois showed that elements with similar properties seemed to occur at regular intervals. His chart included some ions and compounds in addition to elements. His paper also used geological rather than chemical terms and did not include a diagram; as a result, it received little attention until the work of Dmitri Mendeleev.

In 1864, Julius Lothar Meyer, a German chemist, published a table with 44 elements arranged by valency. The table showed that elements with similar properties often shared the same valency. Concurrently, William Odling (an English chemist) published an arrangement of 57 elements, ordered on the basis of their atomic weights. With some irregularities and gaps, he noticed what appeared to be a periodicity of atomic weights among the elements and that this accorded with “their usually received groupings”. Odling alluded to the idea of a periodic law but did not pursue it. He subsequently proposed (in 1870) a valence-based classification of the elements.

English chemist John Newlands produced a series of papers from 1863 to 1866 noting that when the elements were listed in order of increasing atomic weight, similar physical and chemical properties recurred at intervals of eight; he likened such periodicity to the octaves of music. This so termed Law of Octaves was ridiculed by Newlands’ contemporaries, and the Chemical Society refused to publish his work. Newlands was nonetheless able to draft a table of the elements and used it to predict the existence of missing elements, such as germanium. The Chemical Society only acknowledged the significance of his discoveries five years after they credited Mendeleev.

The recognition and acceptance afforded to Mendeleev’s table came from two decisions he made. The first was to leave gaps in the table when it seemed that the corresponding element had not yet been discovered. Mendeleev was not the first chemist to do so, but he was the first to be recognized as using the trends in his periodic table to predict the properties of those missing elements, such as gallium and germanium. The second decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as tellurium and iodine, to better classify them into chemical families. Later, in 1913, Henry Moseley determined experimental values of the nuclear charge or atomic number of each element, and showed that Mendeleev’s ordering actually corresponds to the order of increasing atomic number.

The significance of atomic numbers to the organization of the periodic table was not appreciated until the existence and properties of protons and neutrons became understood. Mendeleev’s periodic tables used atomic weight instead of atomic number to organize the elements, information determinable to fair precision in his time. Atomic weight worked well enough in most cases to (as noted) give a presentation that was able to predict the properties of missing elements more accurately than any other method then known. Substitution of atomic numbers, once understood, gave a definitive, integer-based sequence for the elements, and Moseley predicted (in 1913) that the only elements still missing between aluminium (Z=13) and gold (Z=79) were Z = 43, 61, 72 and 75, all of which were later discovered. The sequence of atomic numbers is still used today even as new synthetic elements are being produced and studied.

I learned, much to my surprise as a young boy that cooking is a form a chemistry. My mother explained to me that when the dry ingredients of a cake are mixed you can take your time, but when you add liquid you have to be quick because the chemical process producing CO2 has started and does not last indefinitely. This was a major turning point in my life – all knowledge can me integrated !!  Here’s a video on chemistry and baking soda. After it I will comment.

The basic idea is fine: make two cake batters except one has baking soda and one does not. Bake them and see what happens. No surprises. The one without baking soda does not rise as much. Note that it does rise a little. Why? Also note she says that the cake without baking soda is heavier than the one with soda. This means she did not conduct a proper experiment. She should have used the same weight of batter for both types of cake. The resultant cakes should be the same weight. The one with baking soda will be fluffier, but not lighter. This experiment gets a C- from me.

Aug 262013
 

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Today is the birthday (1743) of Antoine-Laurent de Lavoisier, a French nobleman whose work in chemistry had a major influence on the nature of scientific inquiry.   Lavoisier is most noted for his discovery of the role oxygen plays in combustion. He recognized and named oxygen (1778) and hydrogen (1783), helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He predicted the existence of silicon (1787) and was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. In the interest of “full disclosure” let me say that I admire his work greatly, but I also lament the fact that the revolution in science he helped usher in has also ushered in an era in which many people believe that if something cannot be measured it is not real.  We have him to thank for the disenchantment of the Western world.

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Lavoisier was born to a wealthy family in Paris, the son of an attorney at the Parlement de Paris. He inherited a large fortune at the age of five with the death of his mother. Lavoisier began his schooling at the Collège des Quatre-Nations (known as the Collège Mazarin) in Paris in 1754 at the age of 11. In his last two years (1760-1761) at the college his scientific interests were aroused, and he studied chemistry, botany, astronomy, and mathematics. In philosophy he was taught by Abbé Nicolas Louis de Lacaille, a distinguished mathematician and observational astronomer who imbued the young Lavoisier with an interest in meteorological observation. He also studied law and received a licentiate, but never practiced law.

Lavoisier’s devotion and passion for chemistry were largely influenced by Étienne Condillac, a prominent French scholar of the 18th century. From 1763 to 1767, he studied geology under Jean-Étienne Guettard. In collaboration with Guettard, Lavoisier worked on a geological survey of Alsace-Lorraine in June 1767. In 1764 he read his first paper to l’Académie Royale des Sciences (Royal Academy of Sciences), France’s elite scientific society, on the chemical and physical properties of gypsum (hydrated calcium sulfate), and in 1766 he was awarded a gold medal by the King for an essay on the problems of urban street lighting. In 1768 Lavoisier received a provisional appointment to l’Académie Royale des Sciences. In 1769, he worked on the first geological map of France.

At age 26, around the time he was elected to l’Académie, Lavoisier bought a share in the Ferme Générale, a tax farming financial company which advanced the estimated tax revenue to the royal government in return for the right to collect the taxes. Lavoisier attempted to introduce reforms in the French monetary and taxation system to help the poor. While in government work, he helped develop the metric system to secure uniformity of weights and measures throughout France. Lavoisier consolidated his social and economic position when, in 1771 at age 28, he married Marie-Anne Pierrette Paulze, the 13-year-old daughter of a senior member of the Ferme Générale. She was to play an important part in Lavoisier’s scientific career—notably, she translated English documents for him, including Richard Kirwan’s Essay on Phlogiston and Joseph Priestley’s research. In addition, she assisted him in the laboratory and created many sketches and carved engravings of the laboratory instruments used by Lavoisier and his colleagues for their scientific works.

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Lavoisier demonstrated with careful measurements that transmutation of water to earth (conceived of at the time as elements) was not possible. He burnt phosphorus and sulfur in air, and proved that the products weighed more than the original. Nevertheless, the weight gained was lost from the air. Thus, in 1789, he established the Law of Conservation of Mass, which is also sometimes called “Lavoisier’s Law.”

Repeating the experiments of Priestley, he demonstrated that air is composed of two parts, one of which combines with metals to form calxes (oxides). In Considérations Générales sur la Nature des Acides (1778), he demonstrated that the “air” (gas) responsible for combustion was also the source of acidity. The next year, he named this portion “oxygen” (Greek for “acid-former”), and the other “azote” (Greek for “no life”). Lavoisier thus has a claim to the discovery of oxygen along with Joseph Priestley and Carl Wilhelm Scheele. He also discovered that the “inflammable air” discovered by Cavendish — which he termed “hydrogen” (Greek for water-former) — combined with oxygen to produce a dew, as Priestley had reported, which appeared to be water. In Reflexions sur le Phlogistique (1783), Lavoisier showed the prevailing phlogiston theory of combustion (that there was an element called phlogiston that was responsible for burning) was untenable.

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Lavoisier worked with Claude Louis Berthollet and others to devise a system of chemical nomenclature which serves as the basis of the modern system of naming chemical compounds. In his  Méthode de nomenclature chimique (Methods of Chemical Nomenclature) (1787), Lavoisier invented the system of naming and classification still largely in use today, including names such as sulfuric acid, sulfates, and sulfites.

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Lavoisier’s Traité Élémentaire de Chimie (Elementary Treatise on Chemistry, 1789) was the first modern chemistry textbook, and presented a unified view of new theories of chemistry, contained a clear statement of the Law of Conservation of Mass, and denied the existence of phlogiston. In addition, it contained a list of elements, or substances that could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. His list, however, also included light, and caloric, which he believed to be material substances. In the work, Lavoisier underscored the observational basis of his chemistry, stating “I have tried…to arrive at the truth by linking up facts; to suppress as much as possible the use of reasoning, which is often an unreliable instrument which deceives us, in order to follow as much as possible the torch of observation and of experiment.” Nevertheless, he believed that the real existence of atoms was philosophically impossible.

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With Pierre-Simon Laplace, Lavoisier used a calorimeter to estimate the heat given off per unit of carbon dioxide produced. They found the same ratio for a flame and animals, indicating that animals produced energy by a type of combustion. Lavoisier believed in the radical theory, believing that radicals, which function as a single group in a chemical reaction, would combine with oxygen in reactions. He believed all acids contained oxygen (later proven wrong). He also discovered that diamond is a crystalline form of carbon. Lavoisier made many fundamental contributions to the science of chemistry. Following Lavoisier’s work, chemistry acquired a strict quantitative nature, allowing reliable predictions to be made. The revolution in chemistry which he brought about was a result of a conscious effort to fit all experiments into the framework of a single theory.

As the French Revolution gained momentum from 1789 on, Lavoisier’s world inexorably collapsed around him. Attacks mounted on the deeply unpopular Ferme Générale, and it was eventually suppressed in 1791. In 1792 Lavoisier was forced to resign from his post on the Gunpowder Commission and to move from his house and laboratory at the Royal Arsenal. On August 8, 1793, all the learned societies, including the l’Académie Royale des Sciences, were suppressed.

He tried to remain aloof from the political arena, no doubt fearful and uncomprehending of the violence he saw. However, on Nov. 24, 1793, the arrest of all the former tax gatherers was ordered. He was branded a traitor by the Convention under Maximilien de Robespierre during the Reign of Terror, in 1794. Lavoisier and the other former tax gatherers were formally brought to trial on May 8, 1794. Lavoisier was convicted with summary justice of having plundered the people and the treasury of France, of having adulterated the nation’s tobacco with water, and of having supplied the enemies of France with huge sums of money from the national treasury. Lavoisier, along with 27 of his former colleagues, was guillotined on the same day. Lavoisier’s importance to science was expressed by Joseph Louis Lagrange who lamented the beheading by saying: “Il ne leur a fallu qu’un moment pour faire tomber cette tête, et cent années peut-être ne suffiront pas pour en reproduire une semblable.” (“It took them only an instant to cut off this head, and one hundred years might not suffice to reproduce its like.”)  He was exonerated 18 months later.

I was very fond of chemistry as a boy (my father was a chemistry teacher), and for several years I had a chemistry lab in my bedroom.  It came as a great revelation to me when I was working in the kitchen with my mother, baking a cake, when she explained that once the baking powder was added to the mix you had to work quickly because moistening the powder set off a chemical reaction (an acid plus a carbonate producing carbon dioxide) that would cause the cake to rise, but would peter out if you waited too long before baking. Who knew?  Since then I have always applied my knowledge of chemistry to cooking in one way or another.  For example, red cabbage has a tendency to turn blue when heated because the heat increases alkalinity in the cabbage.  Solution – add an acid (such as vinegar) during the cooking process and the cabbage stays red.

Let’s use one of the best understood chemical processes in cooking, the Maillard reaction, to make a stew.  The Maillard reaction is a non-enzymatic process of browning that is essential to so much cooking. The browning of old, or peeled, fruits and vegetables is caused by enzymes; browning meat and vegetables by frying or baking is not.  The Maillard reaction (browning) occurs when heat is applied to a combination of amino acids and reducing sugars (chemical components of meats and vegetables).  I choose this as a tribute to Lavoisier because oxygen in the molecules plays a key role (“redox” for those who know some chemistry), in browning (and also in the production of flavor changes). In this recipe I am not using any aromatics such as parsley or thyme because I want the Maillard reaction to speak for itself.

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Tío Juan’s Classic Beef Stew ©

2 lbs (1 kilo) stewing beef
1 onion peeled and coarsely chopped
1 ½ lbs (750 g) potatoes
1 lb (500 g) carrots peeled and diced
½ lb (250 g) mushrooms (halved or quartered depending on size)
1 leek chopped
2 cloves of garlic minced fine
4 tbsps extra virgin olive oil
2 pints (9.5 dl) water
1 tbsp butter
1 tbsp flour
salt to taste

Instructions:

I use a heavy, large, well seasoned cast iron skillet for this dish – my single most important pan in the kitchen (in fact, I have two). Use a large skillet or heavy pot. For the browning, use as little oil as needed to prevent sticking. My quantities are for a large skillet.

Put one tablespoon of olive oil in your pot, and heat on medium low heat.  Add the onions and leeks. Cook slowly, stirring occasionally, until the onions and leeks are caramel colored. In the last minute or two add the garlic, but do not let it brown.  The Maillard reaction makes garlic bitter. Set aside in a large bowl.

Raise the temperature to medium high. Add another tablespoon of olive oil. Sauté the carrots quickly until they are browning but not burnt. Set aside with the onions and leeks.

Peel and dice the potatoes. (Doing this ahead of time will cause them to brown by an enzymatic action, NOT the Maillard reaction.  You can prevent browning by placing cut potatoes in acidulated water, but in this case having the potatoes wet is undesirable.) Cook the potatoes as you did the carrots. Set aside in the vegetable bowl.

Raise the temperature to high. Add another tablespoon of olive oil. Sauté the mushrooms quickly. You must be quick because you want them to brown without overcooking. Set aside with the other vegetables.

Add the last of the olive oil. Quickly brown the meat on all sides.  Make sure the pieces are deeply browned.  Add to the vegetables.

Reduce the heat to medium.  Add the butter and flour to the pan.  Using a wire whisk, stir the melted butter and flour to blend.  Cook this roux slowly, stirring often, until it becomes caramel colored.

Slowly add the water to the roux whisking constantly. It will be very thick at first but if you whisk well no lumps will form.

Return the meat and vegetables to the pot, add salt to taste, and simmer until the meat is tender (about 1 hour).  If you want the carrots and potatoes to be firmer, reserve them separately and add them to the pot in the last 20 minutes.

Serve in bowls piping hot with crusty bread (yes, the brown crust is due to the Maillard reaction as well!)

Serves 4

[Re-bloggers note: this recipe is copyright ©Tío Juan.  Use it by all means, but credit me.]