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Development of the Periodic Table Discovery of most of the elements found in today's periodic table were found in the nineteenth century. It took many Scientists to

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Development of the Periodic Table Discovery of most of the elements found in today's periodic table were found in the nineteenth century. It took many Scientists to assemble a table that recorded all of the elements in terms of atomic mass, and similar trends. However one man seemed to have cracked it, Dimitri Mendeleev. He recorded all the elements known at the time that showed trends, electron number and atomic mass. He managed to predict the properties of other elements that hadn't been discovered and left corresponding gaps for them to be placed. However, it is important to note that Mendeleev did not arrange his table in order of atomic mass. This is what made his table different from the rest. His table was a huge Scientific break through as other Scientists had too many flaws in their versions. The first Scientist to attempt at recording the elements on a table was Johann Dobereiner. He classified them in order of atomic weight (now better known as atomic mass). ...read more.


However, his prediction of the density of Gallium was different to Boisbaudran's. He had asked him to double-check its density as Mendeleev's prediction was 6.0g cm-3 and Boisbaudran's was 4.9g cm-3. Then Boisbaudran found that the actual density of Gallium was 5.93g cm-3, which closely matched Mendeleev's initial prediction! Gallium is an unusual element. It has different properties that can suggest it's both a metal and a non-metal, although it's classed as a metal. Its chemical properties that would suggest it's a metal are: * Its low melting point of 29.78oC so in slightly hotter countries than the UK it would be a liquid metal at room temperature Many Scientists have tried to explain why Gallium has such a low melting point but the only explanation that they can come up with is that it could be due to their being Ga2 molecules in the liquid. * Its range from boiling point to melting point is the largest of any liquid, due to its high boiling point and its low melting point. ...read more.


It's down to it being amazingly stable and its ability to last for years unlike afew seconds. The Quantum theory suggests that the nucleus has separate shells for protons and neutrons. Each shell can only hold a certain number of protons and neutrons (magic numbers): 2, 8, 20, 28, 50, 82, 126. If the nucleus has each of its shells filled to all of these numbers it's a stable element against radioactive decay. Lead, element 82 is very stable as it has this magic number of protons and its isotope 126, also has this magic number of neutrons, making it even more stable. So element 114 should be very stable because Scientists have predicted that there are higher magic numbers, also its isotope 184 would be twice as magic. 994 words Summary: Main Chemical Points Mendeleev created the periodic table in 1869. He left gaps and predicted the properties of undiscovered elements. When they were found they matched his predictions and his table was accepted. Elements today are being artificially formed that don't exist naturally by using a UNILAC accelerator that go beyond Mendeleev's table. 50 words ?? ?? ?? ?? ...read more.

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