Chemical Elements

There are 116 known chemical elements, but some exotic ones produced in laboratories are pending verification.   Of these 116, 91 occur naturally on earth.   The 21 elements directly essential to human life, either as macronutrients (relatively large amounts, measured in milligrams) or micronutrients (small amounts, measured in micrograms), are as follows: calcium, carbon, chlorine, chromium, cobalt, copper, fluorine, hydrogen, iodine, iron, magnesium, manganese, molybdenum, nitrogen, oxygen, phosphorus, potassium, selenium, sodium, sulfur, and zinc.

Note: Contrary to scientific usage, nutritionists refer to 17 of the above elements as "minerals", probably because they are found in minerals, which are rock, found in nature, usually below the soil surface.   Excluded from the nutritionist list are carbon, hydrogen, nitrogen, and oxygen, which are ingested as carbohydrates, fats, proteins, oxygen being also inhaled from the air.   All 21 elements comprise some of the nutrients contained in food.

There are arguably 18 elements essential to plant growth, defining "essential" as (1) being required by the plant to complete its life cycle; and (2) being part of a molecule of a plant part or metabolism.   The macronutrients are carbon, hydrogen, nitrogen, oxygen, phosphorus, sulphur, calcium, magnesium and potassium.   The micronutrients are boron, chlorine, copper, iron, manganese, molybdenum, nickel, zinc, and cobalt.   (Only plants living symbiotically with nitrogen-fixing organisms require cobalt.)

Note: Plant nutritionists usually omit carbon, hydrogen, and oxygen from the above list because they are not "minerals", i.e., they are not elements found in minerals.

Plants take up several other elements from the soil.   Silicon, sodium, and selenium are beneficial, but not essential elements, as defined above.   Other elements taken up by plants appear to be useless, pending further research.   Because nitrogen, phosphorus and potassium are liable to be depleted from soils by the plant or by leaching from the soil, they are frequently added in compounds called fertilizers.   In addition to plant nutrients, sufficient light and limited temperature ranges are essential to plant life.

Since animal life depends on plant life, and boron and nickel are essential to plant life, they are indirectly essential to humans.

Below is a list of 52 elements, listed alphabetically, that have important industrial and health applications.   Included are their corresponding chemical symbols, atomic number, and year of discovery.   A complete list of elements is given in any Periodic Table of Elements. ^{PBS n.p.}