Atomic weights calculating

There was also a problem with affinity. Affinity was an attempt to measure the degree that elements would join together, and some of the groups of elements seemed to have different levels of affinity. This problem would be resolved with the introduction of the concept of valency, which was a measure of the specific number of atoms that could be linked to an atom of an element. Like his assertions about the problem with some of the atomic weight calculations, Mendeleev assumed that future discoveries would prove his system correct. 

FIG. 12. Fifty-four elements known at the time of Berzelius s discoveries are listed here, with the atomic weights calculated on the basis of oxygen at 16.0000. (From The Search for the Elements, Basic Books.)... 

Calculating the formula weight from a formula or molecular model Given the formula of a compound and a table of atomic weights, calculate the formula weight. (EXAMPLES 3.1,3.2)... 

X-ray diffraction from crystals provides one of the most accurate ways of determining Avogadro s number. Silver crystallizes in a face-centered cubic lattice with all atoms at the lattice points. The length of an edge of the unit cell was determined by x-ray diffraction to be 408.6 pm (4.086 A). The density of silver is 10.50 g/cm. Calculate the mass of a silver atom. Then, using the known value of the atomic weight, calculate Avogadro s number. 

Nickel has a face-centered unit cell with all atoms at lattice points and an edge length of 352.4 pm. The density of metallic nickel is 8.91 g/cm. What is the mass of a nickel atom From the atomic weight, calculate Avogadro s number. 

Barium metal has a body-centered cubic lattice with all atoms at lattice points its density is 3.51 g/cm. From these data and the atomic weight, calculate the edge length of a unit cell. 

Rubidium metal has a body-centered cubic structure (with one atom at each lattice point). The density of the metal is 1.532 g/cm. From this information and the atomic weight, calculate the edge length of the unit cell. Now assume that rubidium atoms are spheres. Each corner sphere of the unit cell touches the body-centered sphere. Calculate the radius of a rubidium atom. 

Gravimetric factors are based on the 1993 International Atomic Weights. The factor Ag 0.7526 given in the first line of the table indicates that the weight of precipitate obtained (AgCl) is to be multiplied by 0.7526 to calculate the corresponding weight of silver. 

Corrosion Rate by CBD Somewhat similarly to the Tafel extrapolation method, the corrosion rate is found by intersecting the extrapolation of the linear poi tion of the second cathodic curve with the equihbrium stable corrosion potential. The intersection corrosion current is converted to a corrosion rate (mils penetration per year [mpy], 0.001 in/y) by use of a conversion factor (based upon Faraday s law, the electrochemical equivalent of the metal, its valence and gram atomic weight). For 13 alloys, this conversion factor ranges from 0.42 for nickel to 0.67 for Hastelloy B or C. For a qmck determination, 0.5 is used for most Fe, Cr, Ni, Mo, and Co alloy studies. Generally, the accuracy of the corrosion rate calculation is dependent upon the degree of linearity of the second cathodic curve when it is less than... 

The molecular weight of the salt is calculated fiom the weight w of the platinum, and IV of the salt, accoidmg to the foiniula (the atomic weight of platinum being 195)... 

New lands (1864) was the first to predict correctly the existence of a missing element when he calculated an atomic weight of 73 for an element between silicon and tin, close to the present value of 72.61 for germanium (discovered by C. A. Winkler in 1886). However, his method of detecting potential triads was unreliable and he predicted (non-existent) elements between... 

Consider the substance hydrogen chloride. This compound has the molecular formula HQ. A chemist working with hydrogen chloride, HQ, must often know the weight of a mole of molecules (the molecular weight). This weight is readily calculated from the atomic weights of the two kinds of atoms, H and Cl ... 

In the various editions of his textbook, and in the publications dealing specifically with his predictions, Mendeleev repeatedly gives the example of calculating the atomic weight of the element selenium, a value that was known at the time and which could thus be used to test the reliability of his method. 

A similar activity is found in Mendeleevs first attempt at a periodic system as presented in a hand-written table. If one examines the calculations that he is carrying out one finds again an attempt to compute differences between the atomic weights of elements in the columns of his table. For example Mendeleev writes the number 27 in smaller writing below the symbols for potassium (Zn - K = 65 - 39 = 27) and again below rubidium (Cd-Rb = 112-85 = 27). 

The formula weight is then calculated by multiplying the coefficients by the atomic weights and summing them. 

The atomic weight of silver is 107.9 gmol and its density is 10.49 gcm . Assuming that each silver atom has one conduction electron, calculate... 

Then we calculate the mass from the number of moles and the formula (atomic) weight ... 

Which do we use to calculate the empirical formula of an oxide, the atomic weight of oxygen... 

The law of Dulong and Petit states that the molar heat capacity of crystalline elements is approximately 25 J/mol deg. With this law, we can calculate approximate atomic weights from heat capacity data. 

EXAMPLE 18.14. An element has a specific heat of 0.123 J/g deg. Calculate its approximate atomic weight. 

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