A period 4 element is one of the chemical elements in the fourth row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fourth period contains 18 elements beginning with potassium and ending with krypton – one element for each of the eighteen groups. It sees the first appearance of d-block (which includes transition metals) in the table.
Properties All 4th-period elements are stable, and many are extremely common in the Earth's crust and/or core; it is the last period with no unstable elements. Many transition metals in the period are very strong, and therefore common in industry, especially iron. Some are toxic, with all known vanadium compounds toxic, arsenic one of the most well-known poisons, and bromine a toxic liquid. Conversely, many elements are essential to human survival, such as calcium, the main component in bones.
Atomic structure 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. However, there are exceptions, such as chromium. The first twelve elements—K, Ca, and transition metals—have from 1 to 12 valence electrons respectively, which are placed on 4s and 3d. Twelve electrons over the electron configuration of argon reach the configuration of zinc, namely 3d10 4s2. After this element, the filled 3d subshell effectively withdraws from chemistry and the subsequent trend looks much like trends in the periods 2 and 3. The p-block elements of period 4 have their valence shell composed of 4s and 4p subshells of the fourth (n = 4) shell and obey the octet rule. For quantum chemistry namely this period sees transition from the simplified electron shell paradigm to research of many differently-shaped subshells. The relative disposition of their energy levels is governed by the interplay of various physical effects. 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. Contrariwise, the six elements from gallium to krypton are the heaviest where all electron shells below the valence shell are filled completely. This is no longer possible in further periods due to the existence of f-subshells starting from n = 4.
List of elements
(*) Exception to the Madelung rule
s-block elements
Potassium
Potassium (K) is an alkali metal, underneath sodium and above rubidium, and the first element of period 4. One of the most reactive chemical elements, it is usually found only in compounds. It is a silvery metal that tarnishes rapidly when exposed to the oxygen in air, which oxidizes it. It is soft enough to be cut with a knife and the second least-dense element. Potassium has a relatively low melting point; it will melt under a small open flame. It also is less dense than water, and can, in principle, float (although it will react with any water it is exposed to).
Calcium
Calcium (Ca) is the second element in the period. An alkali earth metal, native calcium is almost never found in nature, because it reacts with water. 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. It also has applications in cells, such as signals for cellular processeses. It is regarded as the most abundant mineral in the human body.
d-block elements
Scandium
Scandium (Sc) is the third element in the period, and is the first transition metal in the periodic table. Scandium is quite common in nature, but difficult to isolate because its chemistry mirrors that of the other rare earth compounds quite closely. Scandium has very few commercial applications, the major exception being aluminium alloys.
Titanium
Titanium (Ti) is an element in group 4. Titanium is both one of the least dense metals and one of the strongest and most corrosion-resistant. As such, it has many applications, especially in alloys with other elements, such as iron. It is commonly used in airplanes, golf clubs, and other objects that must be strong, but lightweight.
Vanadium
Vanadium (V) is an element in group 5. Vanadium is never found in pure form in nature, but is commonly found in compounds. Vanadium is similar to titanium in many ways, such as being very corrosion-resistant, however, unlike titanium, it oxidizes in air even at room temperature. All vanadium compounds have at least some level of toxicity, with some of them being extremely toxic.
Chromium
Chromium (Cr) is an element in group 6. Chromium is, like titanium and vanadium before it, extremely resistant to corrosion, and is indeed one of the main components of stainless steel. Chromium also has many colorful compounds, and as such is very commonly used in pigments, such as chrome green.
Manganese
Manganese (Mn) is an element in group 7. Manganese is often found in combination with iron. Manganese, like chromium before it, is an important component in stainless steel, preventing the iron from rusting. Manganese is also often used in pigments, again like chromium. Manganese is also poisonous; if enough is inhaled, it can cause irreversible neurological damage.
Iron
Iron (Fe) is an element in group 8. Iron is the most common on Earth among elements of the period, and probably the most well-known of them. It is the principal component of steel. Iron-56 has the lowest energy density of any isotope of any element, meaning that it is the most massive element that can be produced in supergiant stars. Iron also has some applications in the human body; hemoglobin is partly iron.
Cobalt
Cobalt (Co) is an element in group 9. Cobalt is commonly used in pigments, as many compounds of cobalt are blue in color. Cobalt is also a core component of many magnetic and high-strength alloys. The only stable isotope, cobalt-59, is an important component of vitamin B-12, while cobalt-60 is a component of nuclear fallout and can be dangerous in large enough quantities due to its radioactivity.
Nickel
… excerpt ends here. Continue reading the full article.
