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---------------------- 2258 - The Periodic Table of elements
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- The periodic table was a large part of my chemistry class in high school. If you wanted to go to college and study something besides politics you had to take physics and chemistry in high school. You even had to take Latin as a second language because the roots of most scientific names are from Latin. Oh , and my high school hours were 8:00 to 4:30 five days a week, with study hall to complete the homework.
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- Chemistry class had us memorize the rows and columns in the Periodic Table and the names of the major the elements. It was not until I got interested in astronomy many years later that I realized that chemistry was created far beyond the flasks and Bunsen burners in the chemistry lab. It was the ingredients that made up outer space as well.
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- The first chemist to come up with the table to organize the elements was Dmitri Mendeleev. He started writing a textbook and pondered ways to group the elements together in order to lighten his load of memorizing them.
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- Mendeleev was a Russian chemist who first spotted an elegant and powerful pattern in the complete list of elements. He recognized that certain elements exhibited similar traits, and that these traits varied regularly, or periodically, with increasing atomic weight.
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- This Valentine’s Day weekend we can celebrate the birth of the Periodic Table that occurred 150 years ago, ( Feb. 17, 1869 according to the Julian calendar used in Russia at that time). That was the date Mendeleev published a chart of the 60-odd elements known at the time, sorted by their weights and properties.
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- His table was called: "An Attempt at a System of Elements, Based on Their Atomic Weight and Chemical Affinity." It has come to be regarded as one of the greatest scientific contributions of all time.
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- His periodic table endured for 150 years? It's an amazing tool that can compress a huge amount of information into one format. It's one of the first things people learn about chemistry. It's in every textbook. It's on the wall of pretty much every chemistry classroom in the world.
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- Dmitri Mendeleev was writing a textbook himself when he came up with the idea. It was a scheme he put together in order to help organize the elements in families so that he didn't have to spend time doing each element individually.
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- He organized the table by increasing atomic weight, but broken into rows. When Mendeleev did that, he saw that certain elements have very similar properties. Some form acids that have similar strength, some form crystals that look the same. In addition to increasing atomic weight, he saw that there is some other pattern that repeats. He invented the term "periodic."
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- He perceived a pattern that could be one of two things. Is it just a convenient teaching tool, or is it a deep pattern in nature? He wasn't the only chemist working on a table 150 years ago. There were six different formulations of the table in the 1860s.
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- However, Mendeleev’s table was unique because it included all the elements. Previous people had put in many or most, but hadn't done all of them because they weren't sure about the atomic weights. Mendeleev made guesses about their weights to fit them in the table. He even had the convection to predict the existence of new elements. When those elements are discovered, his table stands became famous.
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- When Mendeleev started lining up elements with similar properties into columns, he noticed that, in some places, an element seemed to be in the wrong place and should be one column over. When he moved it over, everything worked out.
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- And when there was an empty gap he simply speculated its atomic weight should be about this. He averaged the atomic weights of the elements around it. Within 15 years, three of the elements he predicted in detail were discovered. And they had exactly the properties he said they would.
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- Mendeleev's main competitor at the time was a German named Lothar Meyer. Meyer made a few versions of a similar table in the 1860s, but he never made predictions. He thought it was reckless to guess.
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- Today, the periodic table is organized by atomic number, which is the number of protons in the nucleus. But they didn't know about protons then, so they organized everything by atomic weight. They had what they thought were accurate atomic weights for all the elements, but some of those weights were measured by different systems.
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- Then, in 1860, there was an international meeting of chemists in Germany. Mendeleev happened to be there because he was studying nearby. They propose a unified way of organizing the atomic weights, and when they do that, they correct a whole bunch of atomic weights. Within a year or two, people started seeing these patterns.
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- Mendeleev was born in a Siberian city called Tobolsk, which is almost in the exact center of Russia. He ended up in St. Petersburg for education, and he stayed there most of his life. He taught at the University of St. Petersburg. He traveled a lot and was very boisterous, kind of funny, quick to lose his temper, but also clearly very charismatic and engaging. He was also very politically active. He was in the papers a lot.
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- After he finished the table, he decided he would start keeping all of his mail and all of his letters because he knew he would be famous. He's the kind of person who cared about his legacy and thought of himself quite well.
- He completed his first the table when he was 35, in 1869. Scientists didn't really understand atoms until after Mendeleev died in 1907.
Today we do not organize the table by atomic weight, we organize the table based on quantum theory, on the positions the electrons in the outer shell of an atom. That explains their chemical properties because the electrons determine how they bind with other elements.
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- The electron was discovered in 1897. And, with a better understanding of the structure of the atom, Niels Bohr, the Danish physicist and one of the architects of quantum theory, published a very interesting version of the periodic table that incorporates the insights of the quantum vision of the atom to help explain how the system works. It silenced those who thought the table was just a lucky guess.
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- All of these new elements that have been discovered, the very heavy elements, have been discovered using colliders. The very heavy elements live for a very short period of time measured in microseconds. The heavy elements now take the Table up to 118 in atomic weight.
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- We understand why there are as many columns in the table as there are, and how many rows down we can go before the atom becomes too unstable. We have a table with no gaps, and that gives us a real feeling of understanding nature. But, after chemistry and into particle physics the science gets strange again. There is a lot more to learn to truly understand nature.
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- We are discovering new chemistry in outer space. The first detection was the chemical methylidyne (CH) in the interstellar medium in the 1930s. Observations of molecules in space can help us to understand the chemical evolution of the interstellar medium, the formation of planets, and the physical conditions and processes of the universe around us.
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- We are only just beginning to understand the chemical composition of our universe.
Molecules were detected for the first time in carbon stars, dark clouds, clouds along the line of sight to a background source, and star-forming regions.
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- All of the molecules that have been detected beyond Earth have been spotted in the interstellar or circumstellar medium in our galaxy. In total, 204 different molecules have been identified, ranging in size from two atoms (like methylidyne) to 70 atoms (like rugbyballene, C70).
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- Extragalactic molecules have been discovered. So far 67 of the known interstellar and circumstellar molecules (33%) have also been detected in observations of external galaxies. Only 36 of the known interstellar and circumstellar molecules have been found in protoplanetary disks, in part due to the harsh physical environment around young stars and the challenge of maintaining gas-phase molecules under these conditions.
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- Analyzing these detections we learn that the entirety of the known molecular inventory is constructed from just 16 of the 118 known elements. Be sure to check back in the future to see how our knowledge of the universe’s chemistry changes! The more we explore the more we learn.
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- 1613 - Is another interesting Review that explains why gold is yellow and silver is a mirror.
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- 47 - Review is 10 pages describing each of the elements in the Periodic Table. Element atomic weight 101 is named “mendelevium” is recognition to his contribution to the Periodic Table of Elements.
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- February 5, 2019
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