You will use properties of elements to place them into the appropriate places on the periodic table.
After completing this tutorial, you will be able to complete the following:
All substances are built of atoms. An atom consists of a dense nucleus of positively charged protons and neutral neutrons that is surrounded by a cloud of negatively charged electrons. If all the atoms of a substance have the same properties, then that that substance is an element. We find common elements all around us. In a graphite pencil point, all the atoms are carbon atoms. The shiny liquid in thermometers is composed of mercury atoms. Consider the oxygen we breathe or pure gold and silver-these are all elements.
About ninety elements are found naturally on Earth. Promethium, technetium, and elements with an atomic number greater than 92 are either rare or not found at all on Earth. Some of these are found only in trace amounts in Earth's crust and others have been found only in stars. Further, more than twenty elements have been created in a laboratory, but most of them are unstable and exist for only short periods of time. Some elements are yet to be discovered, and the search for these elements with higher numbers continues. Scientists believe they have created elements 114 and 116, but the discovery of these elements has not been confirmed yet.
Dmitri Mendeleev was a Russian chemist in the late 1800s. As he searched for a way to organize the elements, he arranged all known elements at that time in order of increasing atomic masses and discovered a pattern. Chemical properties found in lighter elements were shown to repeat in heavier elements. Because the pattern was repeated, it was thought of as periodic. Periodic means "repeated in a pattern." Mendeleev had to leave some blank spaces in his periodic table for unknown elements. When he considered the properties and atomic masses of the surrounding elements, he was able to make predictions about the elements that would eventually be placed there. Scientists later discovered some of these missing elements and found that Mendeleev's predictions were extremely close to being accurate.
Mendeleev's arrangement of elements was revolutionary, but it did require some changes. Dutch physicist, Anton van den Broek, proposed that elements should be arranged not according to their atomic masses, as Mendeleev had done, but according to their atomic numbers instead. An English scientist named Henry G.J. Moseley confirmed this hypothesis in the early 1900s, and a new periodic table was conceived. As it turned out, the new arrangement resulted in the repositioning of only a few elements. Our currently periodic table of the elements uses Moseley's arrangement. Columns of elements are called groups, and elements in the same group have similar chemical properties. Rows of elements are called periods, and atomic number increases across a period.
|Approximate Time||20 Minutes|
|Pre-requisite Concepts||Students should be familiar with atomic mass, atomic number, electron configuration, and the structure of the atom.|
|Type of Tutorial||Concept Development|
|Key Vocabulary||atomic mass, atomic model, atomic number|