Phosphorus is a chemical element with the symbol P and atomic number 15. It is a nonmetal that sits on the periodic table between nitrogen (N) and arsenic (As). The name comes from the Greek word φωσφόρος (phōsphoros), meaning “light-bearer”, referring to its ability to glow in the dark.
In terms of abundance, phosphorus is the eleventh most common element in the universe. In nature, it can be found in several different minerals, but most phosphorous commercially produced today comes from phosphate rock. Phosphorus has many uses, including being an essential nutrient for plants and animals, as well as being used in pesticides, detergents, and fertilizers.
Atomic Structure
Phosphorus has 15 electrons arranged in three shells. The first shell has two electrons, the second has eight electrons, and the third has five electrons. Of these 15 electrons, there are five valence electrons on the outermost shell that are responsible for chemical bonding. The atomic structure of phosphorus makes it chemically reactive, which is why it does not occur naturally as a free element on Earth.
Isotopes
There are 30 known isotopes of phosphorus; however, only one – phosphorous-31 – is stable. This means that all other phosphorus isotopes are radioactive and have unstable nuclei. The most common isotope used in research is phosphorous-32 because it decays relatively quickly with a half-life of only 14 days. Other less common isotopes include phosphorous-33 (half-life 25 years), phosphorous-34 (half-life 10^15 years), and phosphorous-35 (half-life 87 years).
Physical Properties
Phosphorus exists in two allotropes: white phosphorus and red phosphorus . White phosphorus is by far the more well known of the two; it is a waxy solid that glows greenish-white when exposed to oxygen in air . It becomes yellow when burned , producing clouds of white smoke . At -85°C (-121°F), white phosphorus changes into a glassy or crystalline solid . Red phosphorus does not have this property; instead , it becomes violet above −80°C (−112°F) . It also ignites at around 240°C (464°F) without oxygen present , whereas white phosphorus needs an oxidizing agent such as air to ignite . Despite these differences , both allotropes have similar molecular structures : each atom is bonded to four other atoms by single covalent bonds . This makes them both polyatomic molecules with tetrahedral shapes . Chemical Properties
When pure , both allotropes of phosphorus are insoluble in water ; however , when mixed with other elements such as chlorine or sulfur , they can form compounds that dissolve readily . For example , sodium phosphate Na3PO4 dissolves easily in water to give neutral solutions ; similarly calcium sulfate CaSO4 also gives neutral solutions upon dissolution . When combined with oxygen forms acids such as H3PO4 (“orthophosphoric acid”) which gives acidic solutions upon dissolution into water ; conversely when combined with bases forms salts called “polyphosphates” which give basic solutions upon dissolution into water e