The periodic table of the chemical elements is a tabular method of displaying the chemical elements.
The main body of the table is a 18 × 7 grid, and elements with the same number of valence electrons are kept together in groups, such as the halogens and the noble gases. These gaps form four distinct rectangular areas or blocks.
Using periodic trends, the periodic table can help predict the properties of various elements and the relations between properties. As a result, it provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences.
A group or family is a vertical column in the periodic table. Groups are considered the most important method of classifying the elements. In some groups, the elements have very similar properties and exhibit a clear trend in properties down the group. Under the international naming system, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The older naming systems differed slightly between Europe and America.
A period or series is a horizontal row in the periodic table. Although groups are the most common way of classifying elements, there are regions where horizontal trends are more significant than vertical group trends, such as the f-block, where the lanthanides and actinides form two substantial horizontal series of elements.
The alkali metals are a group of chemical elements in the periodic table with very similar properties: they are all shiny, soft, silvery, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1.
The alkaline earth metals are a group of chemical elements in the periodic table with very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure and readily lose their two outermost electrons to form cations with charge +2.
In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings:
- The IUPAC definition states that a transition metal is “an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell”.
- Most scientists describe a “transition metal” as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. All elements in the d-block are metals. In actual practice, the f-block is also included in the form of the lanthanide and actinide series
In chemistry, the term post-transition metal is used to describe the category of metallic elements to the right of the transition elements on the periodic table.
A metalloid is a chemical element with properties that are in-between or a mixture of those of metals and nonmetals, and which is considered to be difficult to classify unambiguously as either a metal or a nonmetal.
The halogens or halogen elements are a series of nonmetal elements from group 17 of the periodic table (formerly: VII, VIIA), comprising fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117 (ununseptium), may also be a halogen.
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).