1. Atomic Mass: Molar Mass: The atomic mass is the sum of the mass of protons, neutrons, and electrons. It is the mass of a mole of a substance. It is denoted by m a. The symbol used for it is M. It has a unit of the unified mass unit (u) or the atomic mass unit (amu). G mol −1 is the standard unit for the molar mass. The atomic mass is an.
2. Atomic Mass of Oxygen Atomic mass of Oxygen is 15.9994 u.

Atomic Mass of Oxygen Atomic mass of Oxygen is 15.9994 u. The atomic mass is the mass of an atom. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element.

Oxygen Number Of Protons

Atomic and Molecular Weights

The subscripts in chemical formulas, and the coefficients in chemical equations represent exact quantities. (H_2O), for example, indicates that a water molecule comprises exactly two atoms of hydrogen and one atom of oxygen. The following equation:

[ C_3H_{8(g)} + 5O_{2(g)} rightarrow 3CO_{2(g)} + 4H_2O_{(l)} label{Eq1}]

not only tells us that propane reacts with oxygen to produce carbon dioxide and water, but that 1 molecule of propane reacts with 5 molecules of oxygen to produce 3 molecules of carbon dioxide and 4 molecules of water. Since counting individual atoms or molecules is a little difficult, quantitative aspects of chemistry rely on knowing the masses of the compounds involved.

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Atoms of different elements have different masses. Early work on the separation of water into its constituent elements (hydrogen and oxygen) indicated that 100 grams of water contained 11.1 grams of hydrogen and 88.9 grams of oxygen:

[text{100 grams Water} rightarrow text{11.1 grams Hydrogen} + text{88.9 grams Oxygen} label{Eq2}]

Later, scientists discovered that water was composed of two atoms of hydrogen for each atom of oxygen. Therefore, in the above analysis, in the 11.1 grams of hydrogen there were twice as many atoms as in the 88.9 grams of oxygen. Therefore, an oxygen atom must weigh about 16 times as much as a hydrogen atom:

[ dfrac{dfrac{88.9;g;Oxygen}{1; atom}}{dfrac{111;g;Hydrogen}{2;atoms}} = 16 label{Eq3}]

Hydrogen, the lightest element, was assigned a relative mass of '1', and the other elements were assigned 'atomic masses' relative to this value for hydrogen. Thus, oxygen was assigned an atomic mass of 16. We now know that a hydrogen atom has a mass of 1.6735 x 10^-24 grams, and that the oxygen atom has a mass of 2.6561 X 10^-23 grams. As we saw earlier, it is convenient to use a reference unit when dealing with such small numbers: the atomic mass unit. The atomic mass unit (amu) was not standardized against hydrogen, but rather, against the ¹²C isotope of carbon (amu = 12).

Thus, the mass of the hydrogen atom (¹H) is 1.0080 amu, and the mass of an oxygen atom (¹⁶O) is 15.995 amu. Once the masses of atoms were determined, the amu could be assigned an actual value: Apple keyboard a1843.

1 amu = 1.66054 x 10^-24gramsconversely:1 gram = 6.02214 x 10

Oxygen Atomic Mass Unit

²³

Oxygen Atomic Weight

amu