Chemical compound

Print Cite Share MoreWRITTEN BYRichard O.C. NormanSee All ContributorsRector, Exeter College, University of Oxford. Professor of Chemistry, University of York, England, 1956–87. Author of Principles of Organic Synthesis.See Article History

Chemical compound, any substance composed of identical molecules consisting of atoms of two or more chemical elements.

Lanthanoid, lanthanide

WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History

Alternative Title: lanthanide

Lanthanoid, also called lanthanide, any of the series of 15 consecutive chemical elements in the periodic table from lanthanum to lutetium (atomic numbers 57–71). With scandium and yttrium, they make up the rare-earth metals. Their atoms have similar configurations and similar physical and chemical behaviour; the most common valences are 3 and 4. These elements are also called the lanthanide elements.

Actinoid element – Actinide element

WRITTEN BYLarned B. AspreySee All ContributorsStaff Member, Los Alamos National Laboratory, New Mexico, 1949–86. Author of numerous papers on the actinide, rare-earth, transuranium, and halogen elements.See Article History

Alternative Title: actinide element

Actinoid element, also called actinide element, any of a series of 15 consecutive chemical elements in the periodic table from actinium to lawrencium (atomic numbers 89–103). As a group, they are significant largely because of their radioactivity. Although several members of the group, including uranium (the most familiar), occur naturally, most are man-made. Both uranium and plutonium have been used in atomic weapons for their explosive power and currently are being employed in nuclear plants for the production of electrical power. These elements are also called the actinide elements. However, the International Union of Pure and Applied Chemistry, the international body in charge of chemical nomenclature, prefers the term actinoid, since the -ide ending is usually reserved for negatively charged ions.

Rare-earth element – Inner transition element

WRITTEN BYKarl A. Gschneidner, Jr.See All ContributorsAnson Marston Distinguished Professor, Ames Laboratory, Iowa State University, Ames, Iowa.See Article History

Alternative Titles: inner transition element, rare-earth metal

Rare-earth element, any member of the group of chemical elements consisting of three elements in Group 3 (scandium [Sc], yttrium [Y], and lanthanum [La]) and the first extended row of elements below the main body of the periodic table (cerium [Ce] through lutetium [Lu]). The elements cerium through lutetium are called the lanthanides, but many scientists also, though incorrectly, call those elements rare earths.

Groups IIIb/3 – IIb/12, d- block element – Transition metal

WRITTEN BYF. Albert CottonRobert A. Welch Professor of Chemistry, Texas A&M University, College Station. Author of Chemical Applications of Group Theory.See Article History

Alternative Titles: d-block element, transition element

Transition metal, any of various chemical elements that have valence electrons—i.e., electrons that can participate in the formation of chemical bonds—in two shells instead of only one. While the term transition has no particular chemical significance, it is a convenient name by which to distinguish the similarity of the atomic structures and resulting properties of the elements so designated. They occupy the middle portions of the long periods of the periodic table of elements between the groups on the left-hand side and the groups on the right. Specifically, they form Groups 3 (IIIb) through 12 (IIb).

Group Ia/1 element – Alkali metal

WRITTEN BYFrederick TepperSee All ContributorsGeneral Manager, Instrument Division, Mine Safety Appliances Company, Pittsburgh. Coauthor of Alkali Metal Handling and System Operating Techniques.See Article History

Alternative Titles: Group 1 element, Group Ia element

Alkali metal, any of the six chemical elements that make up Group 1 (Ia) of the periodic table— namely, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkali metals are so called because reaction with water forms alkalies (i.e., strong bases capable of neutralizing acids). Sodium and potassium are the sixth and seventh most abundant of the elements, constituting, respectively, 2.6 and 2.4 percent of Earth’s crust. The other alkali metals are considerably more rare, with rubidium, lithium, and cesium, respectively, forming 0.03, 0.007, and 0.0007 percent of Earth’s crust. Francium, a natural radioactive isotope, is very rare and was not discovered until 1939.

Group IIa/2 element- Alkaline-earth metal

WRITTEN BYCourtenay Stanley Goss PhillipsSee All ContributorsLecturer in Inorganic Chemistry, University of Oxford; Fellow of Merton College, Oxford. Coauthor of Inorganic Chemistry.See Article History

Alternative Titles: Group 2 element, Group IIa element

Alkaline-earth metal, any of the six chemical elements that comprise Group 2 (IIa) of the periodic table. The elements are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

Group 0/VIIIa/18 element – Noble gas, Iner gas, Rare gase

WRITTEN BYGary J. SchrobilgenProfessor of Inorganic Chemistry, McMaster University, Hamilton, Ontario, Canada.Last Updated: Oct 23, 2020 See Article History

Alternative Titles: Group 0 element, Group 18 element, inert gas, rare gas

Noble gas, any of the seven chemical elements that make up Group 18 (VIIIa) of the periodic table. The elements are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and oganesson (Og). The noble gases are colourless, odourless, tasteless, nonflammable gases. They traditionally have been labeled Group 0 in the periodic table because for decades after their discovery it was believed that they could not bond to other atoms; that is, that their atoms could not combine with those of other elements to form chemical compounds. Their electronic structures and the finding that some of them do indeed form compounds has led to the more appropriate designation, Group 18.

Group VIIa/17 element – Halogen group element

WRITTEN BYViktor GutmannSee All ContributorsEmeritus Professor of Inorganic Chemistry, Technical University of Vienna. Author of Halogen Chemistry and others.Last Updated: Oct 23, 2020 See Article History

Alternative Titles: Group 17 element, Group VIIa element, halogen element

Halogen, any of the six nonmetallic elements that constitute Group 17 (Group VIIa) of the periodic table. The halogen elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). They were given the name halogen, from the Greek roots hal– (“salt”) and –gen (“to produce”), because they all produce sodium salts of similar properties, of which sodium chloride—table salt, or halite—is best known.

Group VIa/16 element – Oxygen group element

WRITTEN BYRobert C. BrastedProfessor of Chemistry, University of Minnesota, Minneapolis.See Article History

Alternative Titles: Group 16 element, Group VIa element, chalcogen element, chalcogenide

Oxygen group element, also called chalcogen, any of the six chemical elements making up Group 16 (VIa) of the periodic classification—namely, oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv). A relationship between the first three members of the group was recognized as early as 1829; tellurium was assigned its place by 1865, and polonium was discovered in 1898. In 2000, Russian and American physicists created livermorium, the sixth member of Group 16, in a particle accelerator.