Period 4 element

Conversely, many elements are essential to human survival, such as calcium, the main component in bones.

[2] Progressing towards increase of atomic number, the Aufbau principle causes elements of the period to put electrons onto 4s, 3d, and 4p subshells, in that order.

For quantum chemistry namely this period sees transition from the simplified electron shell paradigm to research of many differently-shaped subshells.

The period's s-block metals put their differentiating electrons onto 4s despite having vacancies among nominally lower n = 3 states – a phenomenon unseen in lighter elements.

(*) Exception to the Madelung rule Potassium (K) is an alkali metal, underneath sodium and above rubidium,[4] and the first element of period 4.

An alkali earth metal, native calcium is almost never found in nature,[citation needed] because it reacts with water.

[8] It has one of the most widely-known biological roles in all animals and some plants, making up structural elements such as bones and teeth.

Scandium is quite common in nature, but difficult to isolate because its chemistry mirrors that of the other rare earth compounds quite closely.

Chromium is, like titanium and vanadium before it, extremely resistant to corrosion, and is indeed one of the main components of stainless steel.

Manganese, like chromium before it, is an important component in stainless steel, preventing the iron from rusting.

Copper is one of the few metals that is not white or gray in color, the only[citation needed] others being gold, osmium and caesium.

Germanium, like silicon above it, is an important semiconductor and is commonly used in diodes and transistors, often in combination with arsenic.

Arsenic, in pure form and some alloys, is incredibly poisonous to all multicellular life, and as such is a common component in pesticides.

Bromine is also quite toxic and corrosive, but bromide ions, which are relatively inert, can be found in halite, or table salt.

Many period 4 elements find roles in controlling protein function as secondary messengers, structural components, or enzyme cofactors.

A gradient of potassium is used by cells to maintain a membrane potential which enables neurotransmitter firing and facilitated diffusion among other processes.

Calcium is a common signaling molecule for proteins such as calmodulin and plays a critical role in triggering skeletal muscle contraction in vertebrates.

Manganese enzymes are utilized by both eukaryotes and prokaryotes, and may play a role in the virulence of some pathogenic bacteria.

Period 4 elements can also be found complexed with organic small molecules to form cofactors.

The most famous example of this is heme: an iron-containing porphyrin compound responsible for the oxygen-carrying function of myoglobin and hemoglobin as well as the catalytic activity of cytochrome enzymes.

[11] Hemocyanin replaces hemoglobin as the oxygen carrier of choice in the blood of certain invertebrates, including horseshoe crabs, tarantulas, and octopuses.