For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. ››More information on molar mass and molecular weight. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all.

The elements of the periodic table sorted by atomic mass

click on any element's name for further information on chemical properties, environmental data or health effects.

The atomic mass is useful in chemistry when it is paired with the mole concept: the atomic mass of an element, measured in amu, is the same as the mass in grams of one mole of an element. Thus, since the atomic mass of iron is 55.847 amu, one mole of iron atoms would weigh 55.847 grams. Water (chemical formula: H2O) is a transparent fluid which forms the world's streams, lakes, oceans and rain, and is the major constituent of the fluids of organisms. As a chemical compound, a water molecule contains one oxygen and two hydrogen atoms that are connected by covalent bonds. ››More information on molar mass and molecular weight. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together.

This list contains the 118 elements of chemistry.

Click here: for a schematic overview of the periodic table of elements in chart form

Do you need to know the weight of some molecules? Try our Molecular Weight Calculator!

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What Is The Atomic Mass Of Water

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Atomic and Molecular Weights

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

[ ce{C3H8(g) + 5O2(g) rightarrow 3CO2(g) + 4H2O(l)} label{Eq1}]

Molecular Weight Of Water

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.

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:

Atomic Mass Of Water Molecule

1 amu = 1.66054 x 10^-24grams conversely: 1 gram = 6.02214 x 10²³amu