Gas periodiska systemet
- De som är gaser är bokstavligen väte, ädelgaserna, kväve och syre som vi har i luften, klor som vi vet är en gas eftersom vi känner dess doft. The periodic table , also known as the periodic table of the elements , is an ordered arrangement of the chemical elements into rows " periods " and columns " groups ". It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law , which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident.
The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics. Vertical, horizontal and diagonal trends characterize the periodic table. Metallic character increases going down a group and from right to left across a period. Nonmetallic character increases going from the bottom left of the periodic table to the top right. The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in ; he formulated the periodic law as a dependence of chemical properties on atomic mass.
As not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the periodic law to predict some properties of some of the missing elements. The periodic law was recognized as a fundamental discovery in the late 19th century. It was explained early in the 20th century, with the discovery of atomic numbers and associated pioneering work in quantum mechanics , both ideas serving to illuminate the internal structure of the atom.
A recognisably modern form of the table was reached in with Glenn T. Seaborg 's discovery that the actinides were in fact f-block rather than d-block elements.
The periodic table and law are now a central and indispensable part of modern chemistry. The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; [ a ] to go further, it was necessary to synthesize new elements in the laboratory. By , the first elements were known, thereby completing the first seven rows of the table; [ 1 ] however, chemical characterization is still needed for the heaviest elements to confirm that their properties match their positions.
New discoveries will extend the table beyond these seven rows , though it is not yet known how many more elements are possible; moreover, theoretical calculations suggest that this unknown region will not follow the patterns of the known part of the table. Some scientific discussion also continues regarding whether some elements are correctly positioned in today's table. Many alternative representations of the periodic law exist, and there is some discussion as to whether there is an optimal form of the periodic table.
Each chemical element has a unique atomic number Z — for "Zahl", German for "number" representing the number of protons in its nucleus. Hydrogen is the element with atomic number 1; helium , atomic number 2; lithium , atomic number 3; and so on. Each of these names can be further abbreviated by a one- or two-letter chemical symbol ; those for hydrogen, helium, and lithium are respectively H, He, and Li. Atoms with the same number of protons but different numbers of neutrons are called isotopes of the same chemical element.
Periodiska system, fast, flytande, gas
For example, carbon has three naturally occurring isotopes: all of its atoms have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if no isotopes occur naturally in significant quantities, the mass of the most stable isotope usually appears, often in parentheses.
In the standard periodic table, the elements are listed in order of increasing atomic number. A new row period is started when a new electron shell has its first electron. Columns groups are determined by the electron configuration of the atom; elements with the same number of electrons in a particular subshell fall into the same columns e. Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well.
Periodic Table Lesson Plans
Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it. Today, elements are known, the first 94 of which are known to occur naturally on Earth at present. Of the 94 naturally occurring elements, 83 are primordial and 11 occur only in decay chains of primordial elements. A few of the latter are so rare that they were not discovered in nature, but were synthesized in the laboratory before it was determined that they do exist in nature after all: technetium element 43 , promethium element 61 , astatine element 85 , neptunium element 93 , and plutonium element The stable elements plus bismuth, thorium, and uranium make up the 83 primordial elements that survived from the Earth's formation.
Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column the alkali metals to the rightmost column the noble gases. The f-block groups are ignored in this numbering. In the United States , the Roman numerals were followed by either an "A" if the group was in the s- or p-block , or a "B" if the group was in the d-block. The Roman numerals used correspond to the last digit of today's naming convention e.
In Europe , the lettering was similar, except that "A" was used for groups 1 through 7, and "B" was used for groups 11 through In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII.