The period in the periodic table is the horizontal row. All elements in a row have the same number of electron shells. Each subsequent element in a period has one more proton and is less metallic than its predecessor. In this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic laws. For example, alkali metals are located in the first column (group 1) and share the same properties, such as high reactivity and the tendency to lose an electron to arrive at a noble gas electronic configuration. By 2016, a total of 118 elements have been found and confirmed.
Modern quantum mechanics describes this periodic trend in the properties of electron shells. When atomic numbers increase, the shells are filled with electrons in the approximate order shown on the right. Filling each shell corresponds to a row in the table.
In block-s and block-p periodic tables, the elements in the same period generally do not show trends and similarities in the property (vertical downward trend trends are more significant). However, in the block-d, trends throughout the period became significant, and in the f-block element showed a high level of similarities throughout the period.
Video Period (periodic table)
Periode
Seven periods of elements occur naturally on Earth. For period 8, which includes elements that can be synthesized after 2016, see the expanded periodic table.
A group in chemistry means a family of things with similarities as different families. There are 7 periods, running horizontally along the periodic table.
Period 1
The first period contains fewer elements than others, with only two, hydrogen and helium. Therefore they do not follow octet rules. Chemically, helium behaves as a noble gas, and is thus taken to be part of a group element 18. However, in the case of its nuclear structure it belongs to block s, and is therefore sometimes classified as a group element 2, or simultaneously both 2 and 18. Hydrogen easily loses and obtains electrons, and behaves chemically as both group 1 and group 17 elements.
- Hydrogen (H) is the most abundant chemical element, comprising about 75% of the mass of the universe. Ionized hydrogen is just a proton. The star in the main sequence consists mainly of hydrogen in its plastic state. Hydrogen elements are relatively rare on Earth, and are industrially produced from hydrocarbons such as methane. Hydrogen can form compounds with most of the elements and is present in water and most organic compounds.
- Helium (He) exists only as a gas except in extreme conditions. This is the second lightest and second most abundant element in the universe. Most of the helium formed during the Big Bang, but new helium was created through nuclear fusion of hydrogen in stars. On Earth, helium is relatively rare, only occurring as a by-product of the natural decay of some radioactive elements. The 'radiogenic' helium is trapped in natural gas in concentrations of up to seven percent by volume.
Period 2
The elements of period 2 involve 2s and 2p orbitals. They are among the most important biological elements other than hydrogen: carbon, nitrogen, and oxygen.
- Lithium (Li) is the lightest metal and the least densest solid element. In an un-ionised state, it is one of the most reactive elements, and is only found naturally in the compound. It is the toughest primordial element that is forged in large numbers during the Big Bang.
- Beryllium (Be) has one of the highest melting points of all light metals. A small amount of beryllium is synthesized during the Big Bang, although most decays or reacts further inside the star to create larger nuclei, such as carbon, nitrogen or oxygen. Beryllium is classified by the International Agency for Cancer Research as group 1 carcinogen. Between 1% and 15% of people are sensitive to beryllium and may develop an inflammatory reaction to their respiratory and skin system, called chronic beryllium disease.
- Boron (B) does not occur naturally as a free element, but in compounds such as borate. It is an important plant micronutrient, which is necessary for strength and development of cell walls, cell division, seed and fruit development, sugar transport and hormone development, although high levels are toxic.
- Carbon (C) is the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen and is the second most common element in the human body with mass after oxygen, the third most number by atomic number. There are a number of almost unlimited compounds containing carbon because of the carbon's ability to form long and stable C-C bond chains. All organic compounds, essential for life, contain at least one carbon atom; combined with hydrogen, oxygen, nitrogen, sulfur, and phosphorus, carbon is the basis of any important biological compound.
- Nitrogen (N) is found mainly because most of the inert diatomic gases, N 2 , which make up 78% of Earth's atmosphere by volume. It is an important component of proteins and hence life.
- Oxygen (O) is made up of 21% of the atmosphere by volume and is required for respiration by all (or almost all) animals, as well as being a major component of water. Oxygen is the third most abundant element in the universe, and oxygen compounds dominate the Earth's crust.
- Fluor (F) is the most reactive element in the unionized state, and hence it has never been found as such in nature.
- Neon (Ne) is a noble gas used in fluorescent lighting.
Period 3
All three-element periods occur in nature and have at least one stable isotope. All but noble gas argon is essential for basic geology and biology.
- Sodium (Na) is an alkali metal. It is present in the Earth's oceans in large quantities in the form of sodium chloride (table salt).
- Magnesium (Mg) is an alkaline earth metal. Magnesium ions are found in chlorophyll.
- Aluminum (Al) is a post-transition metal. It is the most abundant metal in the Earth's crust.
- Silicon (Si) is a metaloid. It is a semiconductor, making it a major component in many integrated circuits. Silicon dioxide is the main constituent of sand. Like Carbon is Biology, Silicon is Geology.
- Phosphorus (P) is a nonmetallic substance that is important for DNA. It's very reactive, and thus never found in nature as a free element.
- Sulfur (S) is nonmetallic. It is found in two amino acids: cysteine ​​â €
- Chlorine (Cl) is a halogen. It is used as a disinfectant, especially in swimming pools.
- Argon (Ar) is a noble gas, making it almost unresponsive at all. Incandescent lamps are often filled with noble gases like argon to preserve filaments at high temperatures.
Period 4
Period 4 includes important biological elements of potassium and calcium, and is the first period in the d-block with a lighter transition metal. These include iron, the toughest element that is planted in the main sequence stars and major components of Earth, as well as other important metals such as cobalt, nickel, and copper. Almost all have biological roles.
Completing the fourth period are post-transition metal zinc and gallium, germanium metalloids and arsenic, and non-metallic selenium, bromine, and krypton.
Period 5
Period 5 has the same number of elements as period 4 and follows the same general structure but with one more transition metal post and one less metal. Of the three toughest elements with biological roles, two (molybdenum and iodine) are in this period; tungsten, in period 6, more severe, along with some early lanthanides. Period 5 also includes technetium, the lightest radioactive element.
Period 6
Period 6 is the first period to include f-block, with lanthanides (also known as rare earth elements), and includes the heaviest stable elements. Many of these heavy metals are toxic and some are radioactive, but platinum and gold are mostly inert.
Period 7
All elements of period 7 are radioactive. This period contains the toughest elements that occur naturally on Earth, plutonium. All subsequent elements in the period have been artificially synthesized. While five of these (from americium to einsteinium) are now available in macroscopic quantities, most are extremely rare, prepared only in microgram quantities or less. Some elements are then only identified in the laboratory in the number of several atoms at a time.
Although the scarcity of many of these elements means that the experimental results are not very broad, the periodic and group trends in behavior seem to be less well defined for period 7 than for other periods. While franium and radium exhibit the distinctive properties of groups 1 and 2, respectively, actinides exhibit a larger range of behavior and oxidation status than lanthanides. The peculiarities of this 7-period may be due to a variety of factors, including the large degree of coupling of spin-orbits and relativistic effects, which are ultimately caused by the very high positive electrical charge of their large atomic nuclei.
Period 8
There is no element of the eighth period that has not been synthesized. An estimated g-block. It is not clear whether all the elements predicted for the eighth period may in fact be physical. Therefore there may not be an eighth period.
Maps Period (periodic table)
References
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