The periodic table of the elements was first introduced in the mid-19th century by Dmitri Mendeleev, who originally represented the elements as periodic functions of their atomic weights. As more elements were discovered, they were arranged in the periodic table in numerical order according to their atomic number, or the number of protons (or electrons) they possessed. The 21st century version of Mendeleev’s original creation also recognizes that periodicity is a consequence of the variation in the elements’ ground state electron configurations, i.e., the number and arrangement of electrons. This ground state configuration is the key to understanding an element’s chemistry. Elements with the same number of valence or outer shell electrons are placed in vertical columns called groups and labeled from 1 to 18. The rows are called periods. Easy-to-use filters allow you to sort by metals, nonmetals, physical states, group, period, and more.
When you click an element tile of interest within this periodic table, you will see additional details and important properties of the element, and be able to select for your experiments various element forms, compounds and, in the case of metals, alloys. See the legend below the table for more details.*
The alkali metals form Group I of the periodic table. Their name refers to the alkaline substances that form when these elements react with water. The most common of these elements are sodium and potassium. Rubidium, lithium, and cesium are more rare, making up, in order, 0.03, 0.007, and 0.0007 percent of the Earth’s crust.
These elements are very reactive, and usually occur in nature already combined with other elements. They have a silver-like luster, high ductility, and are excellent conductors of electricity and heat. Alkali metals have low melting points, ranging from 28.5° to 179°C.
Alkaline Earth metals form Group 2 of the periodic table. Except for radium, all of the elements in this group are used in commercial applications. Magnesium and calcium are two of the six most common elements on Earth, and are essential to some geological and biological processes.
These elements have a shiny gray-white appearance. They are good conductors of electricity and have higher melting and boiling points than the alkali metals. Melting points range from 650° to 1,287°C and boiling points range from 1,090° to 2,471°C.
Post-transition metals are generally considered to be elements in Groups 13, 14, and 15. All of the classifications include the elements gallium, indium, tin, thallium, lead, and bismuth. However, depending on how "post-transition" is defined, this category may contain as few as six or as many as 22 elements.
The post-transition metals share many similarities with the metals, including malleability, ductility, and conductivity of heat and electricity, but are usually softer and have lower melting and boiling points than the transition metals. They have poor mechanical strength, form covalent bonds, and display acid-base amphoterism.
Lanthanides make up the 15 metallic chemical elements with atomic numbers 57 through 71. Called lanthanides because they are chemically similar to lanthanum, these elements and the actinides form the category of rare earth elements. Despite this moniker, these chemicals are fairly abundant in the Earth’s crust. For example, cerium is the 25th most abundant element.
Lanthanides oxidize rapidly in moist air, dissolve quickly in acids, and react slowly with oxygen at room temperature. These elements are used in superconductors and hybrid car components, primarily as magnets and batteries. They are also used in the production of specialty glass.
The 15 metallic elements with atomic numbers 89 to 104, actinium through lawrencium, are referred to as the actinides. All of these elements are radioactive, relatively unstable, and release energy in the form of radioactive decay. However, they can form stable complexes with ligands, such as chloride, sulfate, carbonate, and acetate.
Their radioactivity, toxicity, pyrophoricity, and nuclear criticality make the actinides hazardous to handle. Uranium and plutonium have been used in nuclear plants and in atomic weapons. Some actinides occur naturally in seawater or minerals, but the actinides with atomic numbers 95 to 104 are man-made, created using particle accelerators.
Halogens are the non-metallic elements found in group 17 of the periodic table: and include fluorine, chlorine, bromine, iodine, and astatine. They are the only group whose elements at room temperature include solid, liquid, and gas forms of matter. When halogens react with metals, they produce a range of useful salts, including calcium fluoride, sodium chloride, silver bromide, and potassium iodide.
Since halogens are one electron short of having full shells, they can combine with many different elements. They are highly reactive and can be lethal in concentrated amounts. Commercially, halogens are used in disinfectants, lighting, and drug components.
The noble gases form Group 18 for the first six periods of the periodic table. They’re colorless, odorless, tasteless, and nonflammable. It was originally believed that their atoms could not bond to other elements or form chemical compounds, but that has since been disproven.
Several of these gases are considered very abundant on earth, and all are present in the Earth’s atmosphere. Except for helium and radon, noble gases can be extracted from the air using liquefaction and fractional distillation. Helium is obtained from natural gas wells and radon is a product of radioactive decay.
When Dmitri Mendeleev created the periodic table in the late 19th century, he grouped elements by atomic weight. When grouped by weight, the behavior of the elements appeared to occur in regular intervals or periods. The columns of the modern periodic table represent groups of elements and rows represent the periods. The groups are numbered one through 18. Elements in the same group can be expected to behave in a similar way because they have the same number of electrons in their outermost shell.
Although elements in the same row or period have number of electron shells in common, the properties of the elements are more closely related to the group (vertical columns) to which they belong.