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# Topic: Atomic mass

###### In the News (Thu 21 Mar 19)

 Reference.com/Encyclopedia/Atomic mass unit It is defined to be one twelfth of the mass of an unbound atom of the carbon-12 nuclide, at rest and in its ground state. The chemist John Dalton was the first to suggest the mass of one atom of hydrogen as the atomic mass unit. Before 1961, the physical atomic mass unit (amu) was defined as of the mass of one atom of oxygen-16, while the chemical atomic mass unit (amu) was defined as of the average mass of an oxygen atom (taking the natural abundance of the different oxygen isotopes into account). www.reference.com /browse/wiki/Kilodalton   (741 words)

 Atomic Mass One atomic mass unit (amu) is 1/12 the mass of one atom of A molar mass of an element is the mass of one mole of average atoms of a given element in grams. An isotopic mass is the mass of one atom of a specific isotope in atomic mass units. www.montgomerycollege.edu /~plastas/atommass.htm   (274 words)

 What is atomic mass unit? - a definition from Whatis.com - see also: AMU An atomic mass unit (symbolized AMU or amu) is defined as precisely 1/12 the mass of an atom of carbon-12. In imprecise terms, one AMU is the average of the proton rest mass and the neutron rest mass. The mass of an atom in AMU is roughly equal to the sum of the number of protons and neutrons in the nucleus. whatis.techtarget.com /definition/0,,sid9_gci831527,00.html   (239 words)

 Chem4Kids.com: Glossary: A The atomic mass is the total mass of one atom of an element. Atomic mass is not measured in pounds or grams, scientists used something called Daltons. One Dalton is equal to one-twelfth the mass of a carbon atom. www.chem4kids.com /glossary   (957 words)

 NNDC - Atomic Masses The files corresponding to "The 1993 Atomic Mass Evaluation (I)" and "The 1993 Atomic Mass Evaluation (II)" by G.Audi and A.H. Wapstra [Nuclear Physics A565 p. The files corresponding to "The 1995 Update to the Atomic Mass Evaluation" by G. Audi qnd A.H. Wapstra [Nuclear Physics A595, 409 (1995)] may be found in mass95.zip. He may be calculated using the Qtool; these calculations are based on the 1995 Audi-Wapstra experimental masses when available, otherwise on the FRDM (1992) mass model. www.nndc.bnl.gov /masses   (272 words)

 NationMaster - Encyclopedia: Atomic mass unit   (Site not responding. Last check: ) The unified atomic mass unit, or dalton, is not an SI unit of mass, although it is accepted for use with SI under either name. Before 1961, the physical atomic mass unit was defined as 1/16 of the mass of one atom of oxygen-16, while the chemical atomic mass unit was defined as 1/16 of the average mass of an oxygen atom (taking the natural abundance of the different oxygen isotopes into account). It is defined to be 1/12 of the mass of one atom of carbon-12. www.nationmaster.com /encyclopedia/Atomic-mass-unit   (1342 words)

 Glossary [A-Bomb to AWACS] | atomicarchive.com The atomic bomb is an explosive device that depends upon the release of energy in a nuclear reaction known as fission, which is the splitting of atomic nuclei. The atomic number of an element, which indicates its place in the periodic table of elements, is the number of protons (positively charged particles) in the nucleus of one of its atoms. Atomic number is often symbolized with the letter Z and is shown as a numerical subscript to the left of its chemical symbol. www.atomicarchive.com /Glossary/Glossary1.shtml   (1027 words)

 Atomic mass unit   (Site not responding. Last check: ) The atomic mass unit (amu) unified atomic mass unit (u) or Dalton named after the chemist John Dalton is a small unit of mass used to express atomic masses and molecular masses. It is defined to be 1/12 the mass of one atom of Carbon-12. The relative atomic mass is measured with mass spectrometer. www.freeglossary.com /Atomic_mass_unit   (409 words)

 Atomic mass Summary The relative atomic mass (also known as atomic weight and average atomic mass) is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance. However, since mass defect due to binding energy is minimal compared to the mass of a nucleon, rounding the atomic mass of an isotope tells you the total nucleon count. The pattern in the amounts the atomic masses deviate from their mass numbers is as follows: the deviation starts positive at hydrogen-1, becomes negative until a minimum is reached at iron-56, iron-58 and nickel-62, then increases to positive values in the heavy isotopes, with increasing atomic number. www.bookrags.com /Atomic_mass   (3173 words)

 Highbeam Encyclopedia - Search Results for atomic mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element, as contrasted with atomic mass, which is the mass of any individual isotope. atomic number (proton number) Number of protons in the nucleus of an atom of an element, which is equal to the number of electrons moving around that nucleus. In nuclear notation, such as 7 3 Li, the mass number is the upper number and the atomic number (the number of protons) is the lower one. www.encyclopedia.com /SearchResults.aspx?Q=atomic   (956 words)

 Relative Atomic Mass   (Site not responding. Last check: ) Rather, the mass of an atom is compared with that of an atom of carbon-12. The relative atomic mass of carbon-12 is taken to be 12. In calculating the relative atomic mass of an element with isotopes, the relative mass and proportion of each is taken into account. www.avogadro.co.uk /definitions/ar.htm   (295 words)

 Atomic Structure Overview   (Site not responding. Last check: ) The mass of a neutral atom is measured in atomic mass units (amu), which are based on the mass of the carbon-12 atom. By definition, the mass of the carbon-12 atom is 12.000 amu, and I amu equals n the mass of a carbon- 12 atom. In general, the atomic mass for an element given in tables is an average atomic mass that is the average of the masses of the naturally occurring isotopes of the element. members.aol.com /chemman41/atomic_structure_overview.htm   (2080 words)

 Atomic Theory The reference atomic mass unit is one-twelfth of the mass of the Carbon-12 isotope of carbon. The atomic volume of an element is the relative atomic mass of the element divided by is density. The atomic weight of an element is its relative atomic mass, which is the ratio of the average mass per atom of the naturally occurring form of an element to one twelfth (i.e. www.ucc.ie /academic/chem/dolchem/html/dict/atom.html   (1217 words)

 atomic mass unit Since 1961, by definition the unified atomic mass unit is equal to one-twelfth of the mass of the nucleus of a carbon-12 atom. Although not an SI unit, the unified atomic mass unit is accepted by the CGPM for use with SI. The mass of the unified atomic mass unit is determined experimentally. www.sizes.com /units/atomic_mass_unit.htm   (1060 words)

 Unit 2 - Atomic Structure   (Site not responding. Last check: ) The atomic mass of an element given in the Reference Tables for Chemistry is the weighted average mass of the naturally occurring isotopes of that element. The gram atomic mass (the mass of one mole of atoms) of an element is the mass in grams of Avogadro's number of atoms of that element as it occurs naturally. The atomic mass of a single atom (isotope) such as neon-20 is 19.992 amu while the atomic mass of the element neon (which is the weighted average of all its natural isotopes) is 20.183 amu. dwb.unl.edu /Chemistry/LearningObjectives/NY02.html   (1978 words)

 AllRefer.com - atomic mass (Chemistry) - Encyclopedia atomic mass, the mass of a single atom, usually expressed in atomic mass units (amu). Each proton or neutron weighs about 1 amu, and thus the atomic mass is always very close to the mass number (total number of protons and neutrons in the nucleus). Atomic masses are usually determined by mass spectrography (see mass spectrograph). reference.allrefer.com /encyclopedia/A/atomMas.html   (204 words)

 Molecular Mass In theory, the relative molecular mass or molecular weight of a compound is the mass of a molecule of the compound relative to the mass of a carbon atom taken as exactly 12. In practice, the molecular mass, MM, (molecular weight, MW) of a compound is the sum of the atomic masses (atomic weights) of the atomic species as given in the molecular formula. The relative formula mass, FM, (formula weight, FW) of a compound is the sum of the atomic masses (atomic weights) of the atomic species as given in the formula of the compound. www.ausetute.com.au /mmcalcul.html   (875 words)

 Introductory Terms, Page 2 The Atomic Mass Unit, or a.m.u., is an arbitrarily defined unit of mass created by scientists for measuring the masses of atoms and molecules. one atomic mass unit is equal to 1/12th the mass of one atom of Carbon-12. The values for the atomic weights of the elements are calculated by summing the products of the different individual Isotope Masses multiplied by the decimal equivalent of their percent of abundance values. www.bcpl.net /~kdrews/introterms/intro2.html   (823 words)

 Why is the relative atomic mass of oxygen less than 16?   (Site not responding. Last check: ) The relative atomic mass of oxygen is 15.9994. The atomic mass of an element is defined as the average of the isotopic masses, weighted according to the naturally occurring abundances of the isotopes of the element. For example, since the mass of one atom of oxygen-16 is 1.33291 times the mass of one carbon-12 atom, the mass of one oxygen-16 atom should be equal to 1.33291 x 12 = 15.99492 atomic mass units. www3.fed.cuhk.edu.hk /chemistry/atomic_mass.html   (386 words)

 the mass spectra of elements The relative atomic mass of an element is the weighted average of the masses of the isotopes relative to 1/12 of the mass of a carbon-12 atom. 10.8 is the relative atomic mass of boron. 91.3 is the relative atomic mass of zirconium. www.chemguide.co.uk /analysis/masspec/elements.html   (1035 words)

 Lesson 3-3 Atomic Structure   (Site not responding. Last check: ) For this reason, the masses of the electrons are not considered when calculating the mass number of an atom. The mass number, which is given the symbol A in elemental notation, consists of the total number of protons and neutrons in the nucleus of the atom. The atomic masses shown on the periodic table represent a weighted average based on the relative abundance of each isotope of a particular atom. www.fordhamprep.org /gcurran/sho/sho/lessons/lesson33.htm   (942 words)

 Chemistry : Chapter 1 : Atomic Structure   (Site not responding. Last check: ) However, the mass number, which is the sum of the protons and neutrons, is included as a superscript before the chemical symbol. A reasonable guess for the mass number of the most abundant isotope is to round the average atomic mass to the nearest whole number. E, where A is the mass number and E is the symbol of the element, the number of protons and the number of electrons are equal to the atomic number, Z, and the number of neutrons is A – Z. www.wwnorton.com /chemistry/concepts/chapter1/ch1_2.htm   (614 words)

 Mass and Energy   (Site not responding. Last check: ) Atomic mass is measured differently and its increase can be seen in the chart here, with the references underneath. Atomic masses are dependant upon the strength of the Zero Point Energy. Other work indicates that mass measured macroscopically such as those in deflection experiments, depends on the total energy of the system which remains unchanged as the ZPE increases, whereas the mass measured in an atomic environment is dependent upon the strength of the ZPE. www.setterfield.org /MassandEnergy.htm   (5679 words)

 atomic mass unit Comparison Table   (Site not responding. Last check: ) The masses of atoms and molecules are generally given in atomic mass units. These units are based on a scale in which the mass of carbon 12 is taken to be 12. Atomic masses were originally given as atomic weights on a scale where the mass of the hydrogen atom was unity, later they were based on oxygen or oxygen 16; these scales have all been replaced by the carbon 12 scale. www.site.uottawa.ca:4321 /astronomy/atomicmassunit_table.html   (109 words)

 Chemistry: Average Atomic Mass To find the AVERAGE ATOMIC MASS of an atom, we take into account all of the isotopes that exist and the percentage of each type. The calculation of the average atomic mass is a WEIGHTED AVERAGE. The bottom line is that to find the average atomic mass of copper, we insert the information about copper’s isotopes into the formula and solve. There are two isotopes, so we will be adding the contributions of 2 isotopes. (That’s where the Σ sign comes in. From the calculation, we know that an AVERAGE atom of copper has a mass of 63.55 amu. Notice that in this problem, we would predict that the average is closer to the weight of the lighter isotope. This is because the lighter form of copper is more abundant. www.algebralab.org /practice/practice.aspx?file=Algebra_AverageAtomicMass.xml   (295 words)

 Atomic mass   (Site not responding. Last check: ) Atomic masses (or weights) describe the relative masses of atoms and molecules. An atomic mass is simply a number that indicates the relative mass of an atom. The relative mass of an H atom was established as 1, so the atomic weight of O must be 16. www.pearsoncustom.com /wertz/a_cd/cams/html/c01_early/s06_atom_mass_01.html   (218 words)

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