Elements emit colours when heated because electrons in atoms can have only certain allowed energies.Heating an atom excites its electrons and they jump to higher energy levels. When the electrons return to lower energy levels, they emit energy in the form of light. Every element has a different number of electrons and a different set of energy levels. Thus, each element emits its own set of colours. See, for example, mercury and neon above. Those colours are as distinctive to each element as fingerprints are to people.
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3 7 and 4 also 5 it makes sense
Important changes in the Middle East between the 13th and 15th centuries include the 13 Century end of the First Crusade and the capture/founding of Jerusalem. After that came the rise of the Mongol/Turkish/Ottoman Empire during the 14th Century. The Ottoman transcontinental Empire controlled much of North Africa, Western Asia, and Southeast Europe. This led to the creation of important transcontinental trade routes and a boom of economic trade between the continents.
Pushing the Mongols north and fighting them, and the rebuilding of Beijing caused the Chinese decision to abandon major expeditions.
