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Holli Slye
Now, for a long time, the periodic table rarely added elements. After World War II and the Manhattan Project, however, scientists realized they could use nuclear processes to create elements that never before existed. Essentially, we found a way to stuff more protons into the suitcase.
A moderately unstable element like uranium, with 92 protons, typically decays over billions of years. But these super-stuffed suitcases tend to fall apart in seconds or less. Element 118 lasts only for a fraction of a millisecond.
I kept thinking about how clichéd and pervasive (and fun) the periodic table framework has become, and I thought, "Hey, there's no periodic table of periodic tables." I Googled it and I was right. So I made one. Consider this v 1.0.
March 24, 2010 update: Updated to v 1.1 to fix errors and optimize. The zoomable/clickable version at www.keaggy.com/periodictable is now fully operational, even if it's a bad way to use Flash.
The periodic table as we know it was first published 150 years ago. Its structure is familiar to anyone who has taken a chemistry class in high school or college: the 100 or so elements that make up the universe are arranged in rows according to their atomic number, and in columns according to their properties.
Organizing the periodic table by properties like this may seem obvious, but one of the triumphs of the table is that it relates these easily measurable properties (like boiling points, melting points, reactivity) to atomic-level properties. Mendeleev, the author of the periodic table as we know it, knew many chemical and physical properties of the elements, and even predicted that certain elements should exist before they were discovered (germanium, gallium).1 In order to appreciate how amazing this is, we need to understand a little bit about how atomic structure works.
Coming back to the periodic table, the amazing thing is that 150 years ago, no one knew electrons existed at all, let alone that they had particular energy levels! But the reactivity of the elements is dominated by their valence electron counts, so by organizing the elements according to their reactivity, Mendeleev anticipated this atomic feature that had not been discovered yet. It makes beautiful sense that elements with the same physical and chemical properties have the same number of valence electrons, and ended up organized together on the periodic table.
If we could organize nanoparticles in a periodic table like atoms, we would be able to predict what types of new nano-based materials we could make, and what their properties might be. Chemists love making new compounds, and having guidelines is always helpful on the road to discovery. In the end, Nature is the best chemist of all!
What is not as intuitive is why the size decreases from left to right. But again the construction of the electron configuration gives us the answer. What are you doing as you go across the periodic table? Answer, adding protons to the nucleus and adding electrons to the valence shell of the element. What is not changing as you cross a period? Answer, the inner shell electrons.
Electronegativity may be the most important of the periodic properties you can learn and understand since so many other properties are depend on its value. Electronegativity is an atoms ability to pull electrons towards itself.
The Electron Affinity of an element is the amount of energy gained or released with the addition of an electron. The electronegativity and Electron Affinity increases in the same pattern in the periodic table. Left to right and bottom to top.
The periodic table, also known as the periodic table of the elements, arranges the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which says that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.
Vertical, horizontal and diagonal trends characterize the periodic table. Metallic character increases going down a group and decreases from left to right across a period. Nonmetallic character increases going from the bottom left of the periodic table to the top right.
The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in 1869; he formulated the periodic law as a dependence of chemical properties on atomic mass. As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to predict some properties of some of the missing elements. The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of atomic numbers and associated pioneering work in quantum mechanics both ideas serving to illuminate the internal structure of the atom. A recognisably modern form of the table was reached in 1945 with Glenn T. Seaborg's discovery that the actinides were in fact f-block rather than d-block elements. The periodic table and law are now a central and indispensable part of modern chemistry.
The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist;[a] to go further, it was necessary to synthesise new elements in the laboratory. Today, while all the first 118 elements are known, thereby completing the first seven rows of the table, chemical characterisation is still needed for the heaviest elements to confirm that their properties match their positions. It is not yet known how far the table will go beyond these seven rows and whether the patterns of the known part of the table will continue into this unknown region. Some scientific discussion also continues regarding whether some elements are correctly positioned in today's table. Many alternative representations of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.
Each chemical element has a unique atomic number (Z) representing the number of protons in its nucleus.[3] Most elements have multiple isotopes, variants with the same number of protons but different numbers of neutrons. For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if there are none, the mass of the most stable isotope usually appears, often in parentheses.[4]
In the standard periodic table, the elements are listed in order of increasing atomic number Z. A new row (period) is started when a new electron shell has its first electron. Columns (groups) are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. oxygen, sulfur, and selenium are in the same column because they all have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.[5]
For reasons of space,[16][17] the periodic table is commonly presented with the f-block elements cut out and positioned placed as a distinct part below the main body.[18][16][9] It reduces the number of element columns from 32 to 18.[16]
Both forms represent the same periodic table.[19] The form with the f-block included in the main body is sometimes called the 32-column[19] or long form;[20] the form with the f-block cut out the 18-column[19] or medium-long form.[20] The 32-column form has the advantage of showing all elements in their correct sequence, but it has the disadvantage of requiring more space.[21] The form chosen is an editorial choice, and does not imply any change of scientific claim or statement. For example, when discussing the composition of group 3, the options can be shown equally (unprejudiced) in both forms.[22]
Periodic tables usually at least show the elements' symbols; many also provide supplementary information about the elements, either via colour-coding or as data in the cells. The above table shows the names and atomic numbers of the elements, and also their blocks, natural occurrences and standard atomic weights. For the short-lived elements without standard atomic weights, the mass number of the most stable known isotope is used instead. Other tables may include properties such as state of matter, melting and boiling points, densities, as well as provide different classifications of the elements.[b]
Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth at present.[28][a] Of the 94 natural elements, eighty have a stable isotope and one more (bismuth) has an almost-stable isotope (with a half-life of 2.011019 years, over a billion times the age of the universe).[31][c] Two more, thorium and uranium, have isotopes undergoing radioactive decay with a half-life comparable to the age of the Earth. The stable elements plus bismuth, thorium, and uranium make up the 83 primordial elements that survived from the Earth's formation.[d] The remaining eleven natural elements decay quickly enough that their continued trace occurrence rests primarily on being constantly regenerated as intermediate products of the decay of thorium and uranium.[e] All 24 known artificial elements are radioactive.[19]
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