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In chemistry , valence , also known as valency or valence number , is the number of valence bonds [ 1 ] a given atom has formed, or can form, with one or more other atoms. For most elements the number of bonds can vary. The IUPAC definition limits valence to the maximum number of univalent atoms that may combine with the atom , that is the maximum number of valence bonds that is possible for the given element. [ 2 ]
A chemical symbol is a 1-, 2-, or 3-letter internationally agreed code for a chemical element , usually derived from the name of the element, often in Latin . This is an example of an atomic symbol.
The mass density or density of a material is its mass per unit volume . The symbol most often used for density is ρ (the lower case Greek letter rho ).
The melting point (or, rarely, liquefaction point ) of a solid is the temperature at which it changes state from solid to liquid .
Relative atomic mass (symbol: A r ) is a dimensionless physical quantity , the ratio of the average mass of atoms of an element (from a given source) to 1/12 of the mass of an atom of carbon-12 (known as the unified atomic mass unit ). [ 1 ] [ 2 ] The term is usually used, without further qualification, to refer to the standard atomic weights published at regular intervals by the International Union of Pure and Applied Chemistry (IUPAC) [ 3 ] [ 4 ] and which are intended to be applicable to normal laboratory materials. These standard atomic weights are reprinted in a wide variety of textbooks, commercial catalogues, wallcharts etc., and in the table below.
An explanation of the superscripts and subscripts seen in atomic number notation.
The halogens or halogen elements are a group in the periodic table consisting of five chemically related elements , fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
The noble gases make a group of chemical elements with similar properties: under standard conditions , they are all odorless, colorless, monatomic gases with very low chemical reactivity .
Biochemistry , sometimes called biological chemistry , is the study of chemical processes within, and relating to, living organisms . [ 1 ] By controlling information flow through biochemical signaling and the flow of chemical energy through metabolism , biochemical processes give rise to the complexity of life .
Molecular biology ( pron.: / m ə ˈ l ɛ k j ʊ l ər / ) is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry , particularly genetics and biochemistry .
The mole is a unit of measurement used in chemistry to express amounts of a chemical substance , defined as the amount of any substance that contains as many elementary entities (e.g., atoms , molecules , ions , electrons ) as there are atoms in 12 grams of pure carbon-12 ( 12 C), the isotope of carbon with atomic weight 12. This corresponds to the Avogadro constant , which has a value of 6.022 1 41 7 9(30) × 10 23 elementary entities of the substance. It is one of the base units in the International System of Units , and has the unit symbol mol . [ 1 ] In honor of the unit, chemists often celebrate October 23 (a reference to the 10 23 part of Avogadro's number) as " Mole Day ".
Standard form of the periodic table. The colors represent different categories of elements explained below.
Alchemy is an influential philosophical tradition whose early practitioners' claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base metals into the noble metals gold or silver , as well as an elixir of life conferring youth and longevity. Western alchemy is recognized as a protoscience that contributed to the development of modern chemistry and medicine .
Carbonated water (also known as club soda , soda water , sparkling water , seltzer water , or fizzy water ) is water into which carbon dioxide gas under pressure has been dissolved, a process that causes the water to become effervescent .