Dalton, atomic mass unit

Circumference divided by IT Dalton (atomic mass unit) Da... 

Dalton Atomic mass unit, one Dalton = mass of one hydrogen atom (3.32 X10-24 g). 

The individual collagen ropes are called fibrils, and have an average molecular weight of around 300 000 Daltons (atomic mass units), with a length of 260 nm and a diameter of 1.4-2.0 nm. In the collagen fibres which can be seen... 

Different names are used for the atomic weight by different authors and different abbreviations are used for it. The term dalton is used by some, in honor of John Dalton, and these authors use the abbreviation D. Other authors use the name atomic mass unit. The abbreviation u rather than amu is sometimes encountered. 

Accurate Mass An experimentally determined mass of an ion that is used to determine an elemental formula. For ions containing combinations of the elements C, H, N, O, P, S, and the halogens, with mass less than 200 Da, a measurement with 5 ppm uncertainty is sufficient to uniquely determine the elemental composition. See also related entries on average mass dalton molar mass monoisotopic mass nominal mass unified atomic mass unit. 

Mass See entries on accurate mass average mass dalton molar mass molecular weight monoisotopic mass nominal mass unified atomic mass unit. 

In the graphic form the abscissa represents the mass of ions (to be more precise, the mass-to-charge ratio, m/z), while the ordinate represents the relative intensity of these ions peaks. Atomic mass units (unified atomic mass unit) or daltons are used as units to measure masses of ions, while intensity is represented in percent relative to the base peak in the spectmm or to the total abundance of all the ions in the spectra. The atomic mass unit (dalton) is equal to the mass of one-twelvth of the mass of a 12C atom (1,661 x 10-27 g) (see Chapter 1). 

Note 3 The dalton, symbol Da, is an alternative name for the unified atomic mass unit, Wu, symbol u, i.e., Wu = 1 u. 

The mass number gives the total number of protons and neutrons in an atom of an element, but it does not convey the absolute mass of the atom. To work with the masses of elements, we use comparative masses. Initially, Dalton and the other pioneers of the atomic theory used the lightest element hydrogen and compared masses of other elements to hydrogen. The modern system uses C-12 as the standard and defines one atomic mass unit (amu) as 1/12 the mass of one C-12 atom. One amu is approximately 1.66 X 10 g. This standard means the masses of individual protons and neutrons are slightly more than 1 amu as shown in Table 4.6. 

The atomic mass unit (mu) is also called the dalton (Da) - in honour of John Dalton. In response to the increase in the use of the name dalton for the unified atomic mass unit among chemists, it was suggested by IUPAC that the unified atomic mass unit (u) be renamed the dalton (Da). The definition of the unit would remain unchanged as one-twelfth the mass of a neutral 12C atom in its ground state. The International Union of Pure and Applied Chemistry (IUPAC) proposed that both units, u and Da, should be allowed in official use. 

Atoms are so tiny that even the smallest speck of dust visible to the naked eye contains about 1016 atoms. Thus, the mass of a single atom in grams is much too small a number for convenience, and chemists therefore use a unit called an atomic mass unit (amu), also known as a dalton (Da). One amu is defined as exactly one-twelfth the mass of an atom of and is equal to 1.660 539 X 10 24 g ... 

Dalton (Da) A unit of mass equal to 1/12 of the mass of a carbon-12 atom (compare with atomic mass unit Appendix A). 

Mass Unit The unified atomic mass unit, or u, is the fundamental unit of mass for most mass spectrometrists. The Dalton, or Da, is also generally accepted and is commonly used in descriptions of large, biological molecules. The mass unit is defined as one-twelfth of the mass of carbon-12. Atomic mass unit, or amu, is technically incorrect but still commonly used. The unit Thomson (Th) has been used as a unit of m jz. However, Th is not accepted by most mass spectrometry journals and the International Union of Pure and Applied Chemistry (IUPAC). Therefore, m/z used for labeling the x-axis of mass spectra is unit less. 

In 1808 John Dalton proposed his atomic theory, which included the statement that when atoms of two or more elements combine to form a compound, they combine in a definite ratio by number of atoms and by mass. This is called the law of definite proportions. This provided a means to determine the mass of one atom relative to another. It was necessary to assign a mass to one element to find the mass of another element in a compound. Today we use the most common carbon isotope, assigned a mass of 12.00 atomic mass units (amu), as the basis for comparative weights of the atoms. 

Dalton An atomic mass unit based on 12C = 12 daltons. 

The dalton is not accepted within SI [9], It is perceived as a molecular mass of a specific species. In protocols, molar mass, relative molecular mass or unified atomic mass units should be substituted. The last of these, in conjunction with the SI mass unit, is currently acceptable with an added relative standard uncertainty of 10 6-... 

The subatomic particles differ in mass and charge. Their masses are expressed by the atomic mass unit, u (also called the dalton), which is also used to express the masses of individual atoms, and molecules (aggregates of atoms). The atomic mass unit is defined as a mass equal to exactly 1/12 that of an atom of carbon-12, the isotope of carbon that contains six protons and six neutrons in its nucleus. 

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