part_of reaction inhibitor
___MASK60___ , from the ___MASK41___ " léad ", is a chemical element with atomic number 82 and symbol Pb ( after the Latin , " plumbum "). It has the second highest atomic number of all practically stable elements . As such , lead is located at the end of some decay chains of heavier elements , which in part accounts for its relative abundance : its stability exceeds those of other similarly - numbered elements . ___MASK60___ is a soft , malleable , and heavy metal . Freshly cut lead has a bluish - white color that soon tarnishes to a dull grayish color when exposed to air ; as a liquid , it has a shiny chrome - silver luster . ___MASK60___ ' s density of 11 . 34 g / cm exceeds those of most common materials . A chemical bond is a lasting attraction between atoms that enables the formation of chemical compounds . The bond ___MASK58___ result from the electrostatic force of attraction between atoms with opposite charges , or through the sharing of electrons as in the covalent bonds . The strength of chemical bonds varies considerably ; there are " strong bonds " or " primary bond " such as metallic , covalent or ionic bonds and " weak bonds " or " secondary bond " such as Dipole - dipole interaction , the London dispersion force and hydrogen bonding . A chemical ___MASK69___ is the symbolic representation of a ___MASK73___ in the form of symbols and formulae , wherein the reactant entities are given on ___MASK27___ - hand side and the product entities on the right - hand side . The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers . The first chemical ___MASK69___ was diagrammed by Jean Beguin in 1615 . The electron is a ___MASK42___ , symbol or , with a negative elementary electric charge . Electrons belong to the first generation of the lepton particle family , and are generally thought to be elementary particles because they have no known components or substructure . The electron has a mass that is approximately 1 / 1836 that of the proton . Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin ) of a half - integer value , expressed in units of the reduced Planck constant , "  ". As it is a fermion , no two electrons can occupy the same quantum state , in accordance with the Pauli exclusion principle . Like all matter , electrons have properties of both particles and waves : they can collide with other particles and can be diffracted like light . The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a larger De Broglie wavelength for a given energy . An ion is an ___MASK75___ or a ___MASK72___ in which the total number of electrons is not equal to the total number of protons , giving the ___MASK75___ or ___MASK72___ a net positive or negative electrical charge . Ions can be created , by either chemical or physical means , via ionization . An ___MASK75___ is the smallest constituent unit of ordinary matter that has the properties of a chemical element . Every ___MASK61___ , liquid , gas , and plasma is composed of neutral or ionized atoms . Atoms are very small ; typical sizes are around 100 picometers ( a ten - billionth of a meter , in the short scale ). Nuclear ___MASK37___ is the subfield of ___MASK37___ dealing with radioactivity , nuclear processes , such as nuclear transmutation , and nuclear properties . A ___MASK73___ is a process that leads to the transformation of one set of chemical substances to another . Classically , chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms , with no change to the nuclei ( no change to the elements present ), and can often be described by a chemical equation . Nuclear ___MASK37___ is a sub - discipline of ___MASK37___ that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes may occur . A ___MASK54___ is a form of matter that has constant chemical composition and characteristic properties . It cannot be separated into components by physical separation methods , i . e ., without breaking chemical bonds . Chemical substances can be chemical elements , chemical compounds , ions or alloys . A reaction inhibitor is a substance that decreases the rate of , or prevents , a ___MASK73___ . A catalyst , in contrast , is a substance that increases the rate of a ___MASK73___ .