The periodic table organizes all known chemical elements based on atomic number and electron configuration. Elements are broadly categorized into major classifications, including metals, nonmetals, and metalloids, each exhibiting distinct physical and chemical behaviors. The table is further divided into functional groups, and the Representative Elements form the largest and most chemically diverse collection.
Defining the Representative Elements
Representative Elements are also commonly referred to as the Main Group Elements, distinguishing them from the transition and inner transition metals. Their definition centers on the location of valence electrons, which are the outermost electrons available for chemical bonding. For these elements, valence electrons occupy the outermost s and p electron orbitals of the atom. This configuration fundamentally defines their chemical identity and potential for reaction.
Other elements, such as the Transition Metals and the Lanthanides and Actinides, are defined by the filling of d or f orbitals, which are deeper within the atom’s electron structure. The chemical behavior of representative elements is largely dictated by the readily accessible s and p orbitals. These elements generally have an incomplete outermost shell, which makes them reactive as they seek to achieve a stable, full electron configuration.
Locating the Representative Elements
The Representative Elements occupy two distinct and separated regions, collectively forming the side columns that frame the periodic table. On the far left are Group 1 and Group 2, which constitute the s-block elements, where the outermost s orbital is being filled. Group 1 elements have one valence electron, and Group 2 elements have two valence electrons; both are highly reactive metals (with the exception of Hydrogen).
Separated by the ten columns of the Transition Metals (Groups 3 through 12), the representative elements resume on the right side of the table. This second block comprises Groups 13 through 18, known as the p-block elements. The six columns of the p-block contain metals, metalloids, and nonmetals, including the Noble Gases. The group number in this block can often be used to determine the number of valence electrons.
The physical separation by the transition metals means the representative elements visually bracket the center of the periodic table. This arrangement reflects the order in which electron orbitals are filled, with the s and p orbitals defining the boundaries of each period, or row.
Key Characteristics of Representative Elements
The name “representative” is used because these elements adhere to the general properties expected for their specific vertical group. Their consistent valence electron configurations lead to highly predictable chemical behavior and physical trends throughout the periodic table. This predictability makes them the model for understanding the periodic law, which describes how properties change as atomic number increases.
Moving across a period from left to right, the atoms of the representative elements become smaller, and their ability to attract electrons (electronegativity) increases. This movement also shows a regular gradation from metallic character on the left to non-metallic character on the right. Conversely, moving down a group leads to an increase in atomic size and metallic nature, as the outermost electrons are held less tightly by the nucleus.
The reliable nature of their valence shell allows these elements to exhibit predictable oxidation states, determining how they bond with other elements. This consistency explains why representative elements form a vast majority of the compounds encountered in daily life, such as water, common salts, and organic molecules. They display a wide range of properties, from highly reactive metals to chemically inert gases.
Naming Specific Representative Groups
Within the Representative Elements, several groups have special names that reflect their unique chemical characteristics. Group 1, excluding hydrogen, is known as the Alkali Metals. These are soft, highly reactive metals that readily lose their single valence electron. Group 2 elements are the Alkaline Earth Metals, which are also reactive but possess two valence electrons.
On the far right of the table, Group 17 elements are the Halogens, a group of highly reactive nonmetals that only need one electron to complete their outer shell. The Halogens are notable for forming compounds like table salt (sodium chloride). Group 18 contains the Noble Gases, which are largely inert and unreactive because their outermost electron shells are already full.
The remaining representative element groups are also highly significant. Group 16 elements are sometimes called the Chalcogens, a family including oxygen and sulfur, elements fundamental to biological and geological processes.
Other Named Groups
The remaining groups are named after their top element:
- Group 15 is known as the Nitrogen Group.
- Group 14, the Carbon Group, is the basis of organic chemistry.
- Group 13 is the Boron Group.