valenssimäärä

Valenssimäärä refers to the number of electrons in the outermost electron shell of an atom. These outermost electrons, known as valence electrons, are the ones involved in chemical bonding. The valenssimäärä of an element dictates its chemical properties and how it will interact with other atoms.

For example, elements in Group 1 of the periodic table, such as sodium and potassium, have a valenssimäärä of one. This single valence electron is readily lost, making these elements highly reactive metals that tend to form positive ions. Elements in Group 17, the halogens like fluorine and chlorine, have a valenssimäärä of seven. They are eager to gain one electron to achieve a stable electron configuration, leading them to form negative ions or covalent bonds.

Noble gases, found in Group 18, are characterized by a full outermost electron shell, typically containing eight valence electrons (except for helium, which has two). This stable configuration makes them chemically inert, meaning they rarely participate in chemical reactions.

Understanding the valenssimäärä is fundamental to predicting the types of chemical bonds an element will form, such as ionic or covalent bonds, and the resulting molecular structures. It is a key concept in chemistry for explaining reactivity and the formation of compounds.