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The periodic table is a tabular arrangement of the chemical elements by increasing atomic number which displays the elements so that one may see trends in their properties. The Russian scientist Dmitri Mendeleev is most often credited with inventing the periodic table (1869) from which the modern table is derived. Although Mendeleev's table ordered the elements according to increasing atomic weight rather than atomic number, his table illustrated recurring trends or periodicity in the element properties.
Also Known As: Periodic Chart, Periodic Table of the Elements, Periodic Table of the Chemical Elements
Key Takeaways: Periodic Table Definition
- The periodic table is a tabular arrangement of chemical elements that is arranged by increasing atomic number and groups elements according to recurring properties.
- The seven rows of the periodic table are called periods. The rows are arranged so that metals are on the left side of the table and nonmetals are on the right side.
- The columns are called groups. Group contain elements with similar properties.
The structure of the periodic table makes it possible to see relationships between elements at a a glance and predict properties of unfamiliar, newly discovered, or undiscovered elements.
There are seven rows of the periodic table, which are called periods. Element atomic number increases moving from left to right across a period. Elements toward the left side of a period are metals, while those on the right side are nonmetals.
The columns of elements are called groups or families. Groups are numbered from 1 (the alkali metals) to 18 (the noble gases). Elements within a group display a pattern with respect atomic radius, electronegativity, and ionization energy. Atomic radius increases moving down a group, as successive elements gain an electron energy level. Electronegativity decreases moving down a group because adding an electron shell pushes the valence electrons further from the nucleus. Moving down a group, elements have successively lower ionization energies because it becomes easier to remove an electron from the outermost shell.
Blocks are sections of the periodic table that indicate the outer electron subshell of the atom. The s-block includes the first two groups (the alkali metals and the alkaline earths), hydrogen, and helium. The p-block includes groups 13 to 18. The d-block includes groups 3 to 12, which are transition metals. The f-block consists of the two periods below the main body of the periodic table (the lanthanides and actinides).
Metals, Metalloids, Nonmetals
The three broad categories of elements are metals, metalloids or semimetals, and nonmetals. Metallic character is highest at the bottom lefthand corner of the periodic table, while the most nonmetallic elements are in the upper righthand corner.
The majority of chemical elements are metals. Metals tend to be shiny (metallic luster), hard, conductive, and capable of forming alloys. Nonmetals tend to be soft, colored, insulators, and capable of forming compounds with metals. Metalloids display properties intermediate between those of metals and nonmetals. Toward the right side of the periodic table, the metals transition into nonmetals. There is a rough staircase pattern-starting at boron and going through silicon, germanium, arsenic, antimony, tellurium, and polonium-that identified the metalloids. However, chemists increasingly categorize other elements as metalloids, including carbon, phosphorus, gallium, and others.
Dmitri Mendeleev and Julius Lothar Meyer independently published periodic tables in 1869 and 1870, respectively. However, Meyer had already published an earlier version in 1864. Both Mendeleev and Meyer organized elements by increasing atomic weight and organized elements according to repeating characteristics.
Several other earlier tables were produced. Antoine Lavoisier organized elements into metals, nonmetals, and gases in 1789. In 1862, Alexandre-Emile Béguyer de Chancourtois published a periodic table called the telluric helix or screw. This table was probably the first to organize elements by periodic properties.
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