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Depiction of a hydrogen atom showing the diameter as about twice the Bohr model radius. (Image not to scale) A hydrogen atom is an atom of the chemical element hydrogen.The electrically neutral hydrogen atom contains a single positively charged proton in the nucleus, and a single negatively charged electron bound to the nucleus by the Coulomb force.
For example, the relative isotopic mass of a carbon-12 atom is exactly 12. For comparison, the atomic mass of a carbon-12 atom is exactly 12 daltons. Alternately, the atomic mass of a carbon-12 atom may be expressed in any other mass units: for example, the atomic mass of a carbon-12 atom is 1.992 646 882 70 (62) × 10 −26 kg.
Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] hydrogen gas, molecular hydrogen, or simply hydrogen. It is colorless, odorless, [12] non-toxic, and highly combustible.
The difference is that molecular mass is the mass of one specific particle or molecule, while the molar mass is an average over many particles or molecules. The molar mass is an intensive property of the substance, that does not depend on the size of the sample. In the International System of Units (SI), the coherent unit of molar mass is kg ...
For example, the mass of an unbound atom of the common hydrogen isotope (hydrogen-1, protium) is 1.007 825 032 241 (94) Da, [a] the mass of a proton is 1.007 276 466 5789 (83) Da, [7] the mass of a free neutron is 1.008 664 916 06 (40) Da, [8] and the mass of a hydrogen-2 (deuterium) atom is 2.014 101 778 114 (122) Da. [9]
In mass spectrometry, the molecular mass of a small molecule is usually reported as the monoisotopic mass: that is, the mass of the molecule containing only the most common isotope of each element. This also differs subtly from the molecular mass in that the choice of isotopes is defined and thus is a single specific molecular mass out of the ...
Because a dalton, a unit commonly used to measure atomic mass, is exactly 1/12 of the mass of a carbon-12 atom, this definition of the mole entailed that the mass of one mole of a compound or element in grams was numerically equal to the average mass of one molecule or atom of the substance in daltons, and that the number of daltons in a gram ...
The exact mass of an isotopic species (more appropriately, the calculated exact mass [9]) is obtained by summing the masses of the individual isotopes of the molecule. For example, the exact mass of water containing two hydrogen-1 ( 1 H) and one oxygen-16 ( 16 O) is 1.0078 + 1.0078 + 15.9949 = 18.0105 Da.