Through a series of interactions and animations, learners investigate the properties of metals, metalloids, and non-metals and their location 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. Elements have the same number of protons. We find common elements all around us. In a graphite pencil point, all of the atoms are carbon atoms. The mercury in a thermometer is composed of all mercury atoms. Consider the oxygen we breathe or the gold and silver you see in jewelry. They are all elements.
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 current 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. Elements on the table are color-coded as metals, metalloids, or nonmetals. The metalloids descend in a left-to-right stair-step shape toward right side of the periodic table. Metals are located to the left, and nonmetals are located to the right of the metalloids. As a general rule, elements with five or more electrons on the outer shell are classified as nonmetals, and elements with three or fewer electrons on the outer shell are classified as metals.
|Approximate Time||20 Minutes|
|Pre-requisite Concepts||conductivity, elements, periodic table of elements|
|Type of Tutorial||Concept Development|
|Key Vocabulary||conductor, ductile, ductility|