PERIODIC TABLE
In the periodic table of the elements, elements are arranged in a series of rows (or periods) so that those with similar properties appear in a column. Elements of the same period have the same number of electron shells; with each group across a period, the elements have one more proton and electron and become less metallic. This arrangement reflects the periodic recurrence of similar properties as the atomic number increases. For example, the alkaline metals lie in one group (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. The periodic table of elements has a total of 118 elements.
Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, shells fill with electrons in approximately the order shown at right. The filling of each shell corresponds to a row in the table.
In the s-block and p-block of the periodic table, elements within the same period generally do not exhibit trends and similarities in properties (vertical trends down groups are more significant). However in the d-block, trends across periods become significant, and in the f-block elements show a high degree of similarity across periods.
Modern quantum mechanics explains these periodic trends in properties in terms of electron shells. As atomic number increases, shells fill with electrons in approximately the order shown at right. The filling of each shell corresponds to a row in the table.
In the s-block and p-block of the periodic table, elements within the same period generally do not exhibit trends and similarities in properties (vertical trends down groups are more significant). However in the d-block, trends across periods become significant, and in the f-block elements show a high degree of similarity across periods.
Groups and Families:In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, but the f-block columns (between groups 2 and 3) are not numbered. The elements in a group have similar physical or chemical characteristic of the outermost electron shells of their atoms (i.e., the same core charge), as most chemical properties are dominated by the orbital location of the outermost electron. There are three systems of group numbering. The modern numbering group 1 to group 18 is recommended by the International Union of Pure and Applied Chemistry (IUPAC). It replaces two older naming schemes that were mutually confusing. Also, groups may be identified by their topmost element or have a specific name. For example, group 16 is variously described as oxygen group and chalcogen.
Elements are classified: he periodic table arranges all of the known elements in order of increasing atomic number. Order generally coincides with increasing atomic mass. The different rows of elements are called periods. The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state). The number of electrons in a period increases as one moves down the periodic table; therefore, as the energy level of the atom increases, the number of energy sub-levels per energy level increases. Elements that lie in the same column on the periodic table (called a "group") have identical valance electron configurations and consequently behave in a similar fashion chemically. For instance, all the group 18 elements are inert, or noble gases.
Element groups are either nonmetals or various subsets of metals, but there is no distinct line between the two types of elements. Metal elements are usually good conductors of both electricity and heat. Subsets are based on similar characteristics and chemical properties. Our version of the periodic table uses the most commonly accepted demarcations between the elements
Element groups are either nonmetals or various subsets of metals, but there is no distinct line between the two types of elements. Metal elements are usually good conductors of both electricity and heat. Subsets are based on similar characteristics and chemical properties. Our version of the periodic table uses the most commonly accepted demarcations between the elements