Valence electrons are the electrons located in the outermost energy shell of an atom. These electrons are the primary participants in the formation of chemical bonds, which determines an element’s chemical properties and its reactivity. The arrangement and number of these outer-shell electrons dictate how an atom interacts. Understanding the count of these electrons allows chemists to predict the behavior of any given element. Elements possessing six valence electrons reveal a unique family with distinct characteristics.
The Group 16 Elements
The elements that possess six valence electrons belong to Group 16 of the periodic table. This collection of elements is collectively known as the Chalcogens, sometimes referred to as the oxygen family. The group contains six named elements: oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv).
While they share the same number of valence electrons, the elements exhibit a wide range of physical properties as one moves down the group. Oxygen is a gas and a nonmetal, and sulfur and selenium are typically solids and nonmetals. Tellurium is classified as a metalloid, while polonium is a metal. Polonium is radioactive, and livermorium is a synthetic element that is highly unstable.
Locating Six Valence Electrons on the Periodic Table
The periodic table is arranged so that the number of valence electrons for main group elements can be easily determined by their group number. For elements in Groups 13 through 18, the number of valence electrons corresponds to the unit’s digit of the group number. Therefore, Group 16 elements consistently have six valence electrons.
The structural reason for this six-electron count is defined by the element’s electron configuration. All neutral chalcogens share the general valence shell configuration of \(ns^2np^4\), where ‘\(n\)‘ represents the highest principal energy level. This notation indicates that there are two electrons in the outermost \(s\) orbital and four electrons in the outermost \(p\) orbital, confirming the total of six valence electrons.
This \(ns^2np^4\) configuration places all the chalcogens in the \(p\)-block of the periodic table. Because the outermost shell is partially filled, these elements are chemically reactive as they seek a more stable arrangement. They are only two electrons short of achieving a stable, full outer shell configuration like the noble gases. This requirement strongly influences the chemical behavior of the entire group.
Chemical Characteristics of the Chalcogens
The chemical behavior of the Chalcogens is governed by the octet rule, which describes the tendency of main-group atoms to achieve eight electrons in their outermost shell for maximum stability. Since these elements possess six valence electrons, they have two main ways to satisfy the octet rule. The most common approach involves gaining two electrons from another atom during a chemical reaction.
By acquiring two additional electrons, the atom forms a stable anion with a negative two (\(-2\)) charge. For instance, oxygen forms the oxide ion (\(\text{O}^{2-}\)), and sulfur forms the sulfide ion (\(\text{S}^{2-}\)), both achieving the stable electron configuration of a noble gas. This tendency to gain two electrons is highest for oxygen due to its high electronegativity.
Alternatively, chalcogens can achieve stability by sharing their six valence electrons with other atoms through covalent bonds. When forming a compound, they typically create two single covalent bonds, allowing them to share two electrons to complete their eight-electron shell.
While oxygen primarily exhibits the \(-2\) oxidation state, the heavier chalcogens like sulfur and selenium can also show positive oxidation states, such as \(+4\) and \(+6\). This difference occurs because the larger atoms have accessible \(d\)-orbitals, which allows them to expand their valence shell beyond eight electrons.