The Periodic Table

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   Aluminum      atomic masses      atomic numbers      element      elements      elements      Elements      elements      elements      elements      elements      group      Hydrogen      Hydrogen      left      left      lightest      Mendeleev      metalloids      metaloids      metals      period      periodic table of the elements      right      Russian   

By the mid 1800's, 60 were known. Scientists had quite a bit of information about these . But, the information wasn't organized, so it wasn't very useful. In 1869, a scientist named Dmitri made a chart of the known elements. Since that time, more elements have been discovered and added to the chart. The chart is called the . Every country uses the same periodic table.

In the periodic table, elements are arranged in order of their . With a couple of exceptions, atomic numbers are in the same order as . That is, the lightest element has the lowest atomic number; the heaviest has the highest atomic number.

Look at the periodic table in your book. has an atomic number of 1. It is the element. (AI) has an atomic number of 13. Only 12 are lighter than aluminum.

Each row across the periodic table is called a . All the listed in a row belong to the same period. There are seven periods.

Each column in the periodic table is called a , or family, of . All of the in a group have many similar properties. Each group is identified by a number. For example, the column of elements at the side of the table is Group 1.

can be divided into three types metals, and nonmetals. There are more than nonmetals. In the periodic table, metals are on the , nonmetals are on the . A heavy, step-like line of separates the metals from the nonmetals. is in two places in the periodic table because it can act as a metal or a nonmetal.