Molecular Weight and Valence
By Dr. Donald G. McGahan
An element consists of two basic parts, the nucleus and the electrons which orbit the nucleus. The nucleus primarily contains uncharged neutrons and positive charged protons, while the negative charged electrons orbit the nucleus. In the uncombined or free state, an element has the same number of protons as it has electrons, hence it had no overall electrical charge. Examples of this are metallic iron and copper, and flowers of sulfur.
While elements in an uncombined state are uncharged, most elements have a tendency to gain or to lose electrons. Elements tend to gain or lose electrons until they obtain a stable or noble gas electron configuration (s2p6). The number of electrons that an element gains or loses is its valence. The valence of an element can be thought of as the number of hydrogen ions (H+) that it will replace or combine with in a chemical reaction. You may also think of the valence as the charge on element when it gains or losses electron(s).
A. Major nutrients
|Phosphorous*||+5, +3, -3||H3PO4|
|Sulfur*||-2, +4, +6, +2||H2S, SO2, SO3|
|Nitrogen*||-3, +3, +5, +4, +2||NH3, HNO2, HNO3|
B. Minor nutrients
|Manganese*||+2, +4, +7, +6, +3||MnSO4, MnO2, KMnO|
|Iron*||+2, +3||FeSO4, Fe2O3|
|Copper*||+1, +2||Cu2O, CuO4|
C. Nutrients mainly from water or the atmosphere
|Nutrients from water or atmosphere||Valance||Example|
|Carbon*||-4, 0, +4, +2||CH4, CH12O6, CO2|
|Hydrogen* (usualy in a soils course)||+1||H2O|
|Oxygen* (usually -2 in a soils course)||-1, -2||H2O2, H2O|
D. Other miscellaneous elements
*These elements commonly show variable valences and the valence will usually be calculated from the other elements in the compound.