Atomic and physical properties

156 MeV, ,ean 0.049 MeV) with a half-life of 5715 30 and this is sufficiently long to enable a steady-state equilibrium concentration to be established in the biosphere. Plants and animals therefore contain 1.2 x 10 °% of their carbon as whilst they are living, and this leads to a /3-activity of 15.3 counts per min per gram 

Of these, all are experimentally observable except the Svaience state level which is a calculated value for a carbon atom with 4 unpaired and uncorrelated electron spins this is a hypothetical state, not amenable to experimental observation, but is helpful in some discussions of bond energies and covalent bonding theory. 

The electronegativity of C is 2.5, which is fairly close to the values for other members of the 

Michels, Dating Methods in Archeology, Seminar Press, New York, 1973, 230 pp., S. Fleming, Dating in Archeology A Guide to Scientific Techniques Dent, London, 1976, 272 pp. 

The single-bond covalent radius of C can be taken as half the interatomic distance in diamond, i.e. r(C) = 77.2pm. The corresponding values for doubly-bonded and triply-bonded carbon atoms are usually taken to be 66.7 and 60.3 pm respectively though variations occur, depending on details of the bonding and the nature of the attached atom (see also p. 292). Despite these smaller perturbations the underlying trend is clear the covalent radius of the carbon atom becomes smaller the lower the coordination number and the higher the formal bond order. 

Carbon occurs predominantly as the isotope but there also is a small amount of the concentration of varies slightly from 0.99 to 

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General similarities and trends in the chemical properties of the elements had been noticed increasingly since the end of the eighteenth century and predated the observation of periodic variations in physical properties which were not noted until about 1868. However, it is more convenient to invert this order and to look at trends in atomic and physical properties first. 

These, though more difficult to describe quantitatively than the trends in atomic and physical properties described in the preceding subsection, also become apparent when the elements are compared in each group and along each period. Such trends will be discussed in detail in later chapters and it is only necessary here to enumerate briefly the various types of behaviour that frequently recur. 

Atomic and physical properties Table 16.1 Production and properties of long-lived Po isotopes... 

Several atomic and physical properties of the elements are given in Table 16.2. The trends to larger size, lower ionization energy and lower electronegativity are as expected. The trend to metallic conductivity is also noteworthy indeed, Po resembles its horizontal neighbours Bi, Pb and T1 not only in this but in its moderately high density and notably low mp and bp. 

Table 16.2 Some atomic and physical properties of selenium, tellurium and polonium...

Atomic and physical properties Table 17.4 Physical properties of the halogens... 

Atomic and physical properties of the elements Table 18.1 Some properties of the noble gases... 

Table 27.1 lists some of the important atomic and physical properties of these three elements. The prevalence of naturally occurring isotopes in this triad limits the precision of their quoted atomic weights, though the value for Ni was improved by more than two orders of magnitude in 1989... 

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