PERIODIC TABLE WITH EXACT MOLAR MASS ZIP FILE
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Table 3.5 Selected Atomic Masses of Some Elements Element Name The sum is the weighted average and serves as the formal atomic mass of the element. A weighted average is found by multiplying each mass by its fractional occurrence (in decimal form) and then adding all the products. What do we mean by a weighted average? Well, consider an element that consists of two isotopes, 50% with mass 10 u and 50% with mass 11 u. of an element is a weighted average of the masses of the isotopes that compose an element. The atomic mass The weighted average of the masses of the isotopes that compose an element. Thus, although it is easy to speak of the mass of an atom, when talking about the mass of an element, we must take the isotopic mixture into account. What is the mass of an element? This is somewhat more complicated because most elements exist as a mixture of isotopes, each of which has its own mass. More exact masses are found in scientific references-for example, the exact mass of uranium-238 is 238.050788 u, so you can see that we are not far off by using the whole-number value as the mass of the atom. Thus, the mass of carbon-12 is about 12 u, the mass of oxygen-16 is about 16 u, and the mass of uranium-238 is about 238 u. There will not be much error if you estimate the mass of an atom by simply counting the total number of protons and neutrons in the nucleus (i.e., identify its mass number) and ignore the electrons. By this scale, the mass of a proton is 1.00728 u, the mass of a neutron is 1.00866 u, and the mass of an electron is 0.000549 u. (u some texts use amu, but this older style is no longer accepted) is defined as one-twelfth of the mass of a carbon-12 atom, an isotope of carbon that has six protons and six neutrons in its nucleus. The atomic mass unit One-twelfth of the mass of a carbon-12 atom. For macroscopic objects, we use units such as grams and kilograms to state their masses, but these units are much too big to comfortably describe the masses of individual atoms and molecules. Individual atoms and molecules, however, are very small, and the masses of individual atoms and molecules are also very small.

Express the masses of atoms and molecules.īecause matter is defined as anything that has mass and takes up space, it should not be surprising to learn that atoms and molecules have mass.

PERIODIC TABLE WITH EXACT MOLAR MASS ZIP FILE

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Periodic table with exact molar mass