Table of Atomic Masses

ELEMENT SYMBOL ATOMIC NUMBER ATOMIC MASS 

Acid-base indicator A substance that changes color in the presence of an acid or a base. 

Amphoteric A compound that can act as an acid or a base depending on the circumstances. 

Acid rain Rain or any other form of precipitation that is strongly acidic due to sulfur and nitrogen compounds released through the burning of fossil fuels, particularly coal. 

Addition reaction Reaction in which atoms are added to reactants, often at carbon-carbon double or triple bonds. 

Acid A compound that forms hydrogen ions (H+) when dissolved in water. 

Activation energy Energy needed to start a chemical reaction. 

Actinides The elements from actinium (atomic number 89) to nobelium (atomic number 102). 

Alchemy A mixture of chemistry and philosophy practiced in the ancient world its main goals were to transform metals into gold and find chemical potions that would cure disease and lengthen life. 

Absolute temperature The lowest possible temperature is absolute 0, which is -273° C. The absolute temperature scale starts there. The unit of measurement is the kelvin (K). 

Alcohols A family of organic compounds that have an OH group attached to a carbon atom. A common alcohol is ethanol, 

Acids Substances that yield hydrogen ions when dissolved in water these substances also accept electron pairs to form covalent bonds. 

Alchemy A science practiced during the Middle Ages and Renaissance that involved efforts to turn metals into gold. 

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Dalton proposed his atomic theory in 1803. He published a table of atomic masses. The errors (due to errors in his assumptions) in his first table were corrected in 1858. 

Table of Atomic Masses, ed. J. W. Guthrie monograph SCR-245A from US Atomic Energy Commission 1961. 955, 956... 

Ans. The atomic mass of bromine is 79.90 amu, as seen in the periodic table or a table of atomic masses. The molecular mass of bromine, corresponding to Br2, is twice that value, 159.8 amu. 

Using similar reasoning for other compounds, Dalton prepared the first table of atomic masses (formerly called atomic weights by chemists, since mass is usually determined by comparison to a standard mass—a process called weighing ). Many of the masses were later proved to be wrong because of Dalton s incorrect assumptions about the formulas of certain compounds, but the construction of a table of masses was an important step forward. 

A 60.00-g sample of a dry-cleaning fluid was analyzed and found to contain 10.80 g carbon, 1.36 g hydrogen, and 47.84 g chlorine. Determine the empirical formula of the compound using a table of atomic masses. 

For most practical purposes we are interested in the masses of reactants and products, because those are the quantities that are directly measured. In this case, the molar masses (calculated from a table of atomic masses) are used to convert the number of moles of a substance (in moles) to its mass (in grams), as illustrated by Example 2.6. Sometimes, however, we are also interested in knowing the number of molecules in a sample. The mole allows us to convert easily from mass to numbers of molecules as follows ... 

One way to remove, or strip, the parenthetical uncertainties in the table of atomic masses is to use Excel s Find/Replace function. We will illustrate this approach with a few of the entries. Copy the atomic masses from hydrogen through copper, including the uncertainties, to column F, cells F2 F30. Now highlight cells F2 F30. Go to the Edit menu and choose Replace. This should bring up the Find and Replace window shown below. Make sure the Replace tab is selected as shown. 

Devise an Excel formula for elements 43, 61, 84 to 89, and 93 to 114 that will automatically remove the square brackets from the lUPAC table of atomic masses and eliminate the VALUE error described in Section 3B-2. 

In 1808, from his observations, the English scientist Dalton was able to add a very important general theory on particles. In his work, A New System of Chemical Philosophy [14], he combined the idea of elements and the atomic concept and created the first table of atomic masses ... 

Because we are concerned with elements, let s use iron, Fe, as our example. From the table of atomic masses, we find that the atomic mass of iron is 55.85 amu. In terms of iron ... 

These problems have both answers and solutions given. The required atomic masses are taken from the table of atomic masses. 

Consult the table of atomic masses or a periodic table for the necessary atomic masses. 

Empirical formulas can also be calculated from the mass of each element in a sample of a compound. Analysis of a sample of a compound shows that it contains 1.179 g Na and 0.821 g S. You could calculate the percent of each element from these numbers, but that s not necessary. The mass of each element is converted directly to moles for the empirical formula. From the table of atomic masses, we find the molar masses are 22.99 g for Na and 32.07 g for S. 

The atomic masses of many elements have been accurately determined to five or six significant figures. However, for our purposes we will normally use atomic masses accurate only to four significant figures (see the table of atomic masses inside the front... 

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