Sodium atomic weight

Heavy metals are those in the series of metals that have a greater atomic weight than sodium (atomic weight 23.0). Heavy metals include lead, mercury, aluminium, chromium, etc. Heavy metals can be involved in many reactions e.g., 2,4-dinitroresorcinol is used to create heavy metal complexes. 

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but... 

It is evident from the above equation that each gram-atomic weight of iodine in thyroid is converted to 1 mol of iodate and finally to 3 mol or 6 equivalent of iodine. Therefore, the equivalent weight of the iodine present in the dried thyroid gland is 21.15 g (i.e., 1/6 x 127 At. wt. of I2). Hence, each millilitre of 0.01 N sodium thiosulphate is equivalent to 0.0002115 g of iodine (i.e., 0.01 x 0.02115 g). 

A remarkable property of the atomic weights was discovered, in the sixties, independently by Lothar Meyer and Mendeleeff. They found that the elements could be arranged in rows in the order of their atomic weights so that similar elements would be found in the same columns. A modernised form of the Periodic Table will be found on pp. 106, 107. It will be noticed, for example, that the "alkali" metals, Lithium, Sodium, Rubidium and Caesium, which... 

ISOTOPES Sodium has 14 isotopes. The only stable isotope of sodium has an average atomic weight of 23 ( Na) and makes up about 100% of all the isotopes of the element sodium found on Earth. All the other 13 isotopes (from Na to Na) are radioactive with relatively short half-lives and thus are unstable. 

For nonmolecular substances like sodium chloride, the use of the word mole, with its connotation of molecules, is inappropriate. A comparable unit, the gram formula weight, is used it is defined as the sum in grams of the atomic weights of all the atoms in the chemical formula of the substance. For sodium chloride (NaCl), one gram formula weight is calculated as... 

Mendeleev arranged the elements into seven groups. Lithium (atomic weight 7) was followed by beryllium (9), boron (11), carbon (12), nitrogen (14), oxygen (16), and fluorine (19). The next element in order of atomic weight was sodium (23), which had properties similar to those of lithium. Therefore, Mendeleev pinned the card for sodium under that for lithium. Six more cards were placed in the second row, ending with chlorine under fluorine. He continued in... 

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