The electronic configuration of an element provides information about the arrangement of electrons within its atoms. Valency, on the other hand, refers to the number of electrons an atom of an element can gain, lose, or share in order to achieve a stable electron configuration.
The valency of an element is often determined by the number of valence electrons, which are the electrons in the outermost energy level (shell) of an atom. The outermost energy level is significant because it plays a crucial role in chemical bonding and determining the reactivity of an element.
The number of valence electrons can be determined by looking at the group (column) number of the element in the periodic table. In general, elements in the same group have similar valence electron configurations, and therefore, similar valencies. Here are some common trends:
Group 1 elements (alkali metals) have one valence electron and tend to lose this electron to achieve a stable electron configuration like the noble gas in the previous period.
Group 2 elements (alkaline earth metals) have two valence electrons and tend to lose these two electrons to attain a stable configuration.
Group 13 elements have three valence electrons and may lose these electrons or share them in chemical bonds.
Group 14 elements (carbon group) have four valence electrons and can share or gain/lose electrons to reach a stable configuration.
Group 15 elements (nitrogen group) have five valence electrons and tend to gain three electrons or share electrons to achieve stability.
Group 16 elements (oxygen group) have six valence electrons and tend to gain two electrons or share electrons to achieve stability.
Group 17 elements (halogens) have seven valence electrons and typically gain one electron to achieve a stable octet configuration.
Group 18 elements (noble gases) have a stable electron configuration and tend not to form compounds due to their complete outermost energy level.
It's important to note that the concept of valency can become more complex in transition metals and other elements that can exhibit variable oxidation states. However, for most main group elements, the valency is directly related to their electron configuration, specifically the number of valence electrons.