Show In the periodic table of the elements, each numbered column is a group. In chemistry, a group (also known as a family[1]) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table; the f-block columns (between groups 2 and 3) are not numbered. The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms (i.e., the same core charge), because most chemical properties are dominated by the orbital location of the outermost electron. There are three systems of group numbering for the groups; the same number may be assigned to different groups depending on the system being used. The modern numbering system of "group 1" to "group 18" has been recommended by the International Union of Pure and Applied Chemistry (IUPAC) since about 1990. It replaces two older incompatible naming schemes, used by the Chemical Abstract Service (CAS, more popular in the US), and by IUPAC before 1990 (more popular in Europe). The system of eighteen groups is generally accepted by the chemistry community, but some dissent exists about membership of several elements. Disagreements mostly involve elements number 1 and 2 (hydrogen and helium), as well as inner transition metals. Groups may also be identified using their topmost element, or have a specific name. For example, group 16 is also described as the "oxygen group" and as the "chalcogens". An exception is the "iron group", which usually refers to "group 8", but in chemistry may also mean iron, cobalt, and nickel, or some other set of elements with similar chemical properties. In astrophysics and nuclear physics, it usually refers to iron, cobalt, nickel, chromium, and manganese. Group names[edit]In history, several sets of group names have been used:[2][3]
a Group 1 is composed of hydrogen (H) and the alkali metals. Elements of the group have one s-electron in the outer electron shell. Hydrogen is not considered to be an alkali metal as it is not a metal, though it is more analogous to them than any other group. This makes the group somewhat exceptional. n/a Do not have a group number b The composition of group 3 is not agreed among sources: see Periodic table#Group 3 and Group 3 element#Dispute on composition. General inorganic chemistry texts usually put scandium (Sc), yttrium (Y), lanthanum (La), and actinium (Ac) in group 3, so that Ce–Lu and Th–Lr become the f-block between groups 3 and 4. However, sources that study the matter usually put scandium, yttrium, lutetium (Lu), and lawrencium (Lr) in group 3, as shown here. Some sources, including IUPAC, currently follow a compromise that puts La–Lu and Ac–Lr as the f-block rows, leaving the heavier members of group 3 ambiguous. The arrangement with Sc, Y, Lu, and Lr in group 3 has been recommended by a 2021 IUPAC preliminary report on this question. c Group 18, the noble gases, were not discovered at the time of Mendeleev's original table. Later (1902), Mendeleev accepted the evidence for their existence, and they could be placed in a new "group 0", consistently and without breaking the periodic table principle. d Authors differ on whether roentgenium (Rg) is considered a coinage metal. It is in group 11, like the other coinage metals, and is expected to be chemically similar to gold.[4] On the other hand, being extremely radioactive and short-lived, it cannot actually be used for coinage as the name suggests, and on that basis it is sometimes excluded.[5] r Group name as recommended by IUPAC.
Some other names have been proposed and used without gaining wide acceptance:
CAS and old IUPAC numbering (A/B)[edit]Two earlier group number systems exist: CAS (Chemical Abstracts Service) and old IUPAC. Both use numerals (Arabic or Roman) and letters A and B. Both systems agree on the numbers. The numbers indicate approximately the highest oxidation number of the elements in that group, and so indicate similar chemistry with other elements with the same numeral. The number proceeds in a linearly increasing fashion for the most part, once on the left of the table, and once on the right (see List of oxidation states of the elements), with some irregularities in the transition metals. However, the two systems use the letters differently. For example, potassium (K) has one valence electron. Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains two valence electrons. In the old IUPAC system the letters A and B were designated to the left (A) and right (B) part of the table, while in the CAS system the letters A and B are designated to main group elements (A) and transition elements (B). The old IUPAC system was frequently used in Europe, while the CAS is most common in America. The new IUPAC scheme was developed to replace both systems as they confusingly used the same names to mean different things. The new system simply numbers the groups increasingly from left to right on the standard periodic table. The IUPAC proposal was first circulated in 1985 for public comments,[2] and was later included as part of the 1990 edition of the Nomenclature of Inorganic Chemistry.[11] See also[edit]
References[edit]
Further reading[edit]
What is group 5 called in the periodic table?Group 5A (or VA) of the periodic table are the pnictogens: the nonmetals nitrogen (N), and phosphorus (P), the metalloids arsenic (As) and antimony (Sb), and the metal bismuth (Bi).
What is period 4 on the periodic table called?The period 4 transition metals are scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn).
What are the 4 group names on the periodic table?Groups are numbered 1–18 from left to right. The elements in group 1 are known as the alkali metals; those in group 2 are the alkaline earth metals; those in 15 are the pnictogens; those in 16 are the chalcogens; those in 17 are the halogens; and those in 18 are the noble gases.
What is each group called in the periodic table?Families of the Periodic Table. On the periodic table, there are families which are groups of elements with similar properties. These families are alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, halogens, noble metals, and noble gases.
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