Elements versus atoms

Figure 15.10 Half-lives of the longest-lived isotope of each element versus atomic number Z circa 1970. (Figure also appears in color figure section.)...

Figure 6-2 A plot of first ionization energies for the first 38 elements versus atomic number.

Experimentally, electron affinity is determined by removing the additional electron from an anion. In contrast to ionization energies, however, electron affinities are difficult to measure because the anions of many elements are unstable. Table 8.3 shows the electron affinities of some representative elements and the noble gases, and Figure 8.12 plots the electron affinities of the first 56 elements versus atomic number. The overall trend is an increase in the tendency to accept electrons (electron affinity... 

A rather interesting plot (see fig. 9.6a) is the initial melting slope dT/dP of the rare earth elements versus atomic number. In this plot the divalent and trivalent lines are well established from the slopes of Eu and Yb and from La, Gd and Lu respectively. The quadrivalent line drawn parallel to these is perhaps not unreasonable. The deviations of the data points from the trivalent line, of Sm... 

Figure 5-2 A plot of first ionization energies for the first 38 elements versus atomic number.The noble gases have very high first ionization energies, and the 1A metals have low first ionization energies. Note the similarities in the variations for the Period 2 elements, 3 through 10, to those for the Period 3 elements,...

Even Boyle, therefore, plays on both sides of any alleged divide between atomic theory and principles or elements. Thus, we can conclude that, while tempting, it is ultimately too superficial to try to distinguish chemistry from physics along the line of elements versus atoms, or between a philosophy of matter characterized by inherent principles and a vision based on homogeneous but discontinuous matter. First, as we noted in Chapter 7, the clash between these two traditions preceded the emergence of the modern... 

Fig. I. (a) Atomic abundances relative to Si = Iff versus atomic weight for die sun and similar main-sequence stars, (b) Cross-section factor S (in MeV-vams) versus cenler-of-momcnlum energy (in MeV) for l C(rt. y lO Dashed and solid curves are theoretical extrapolations of Munster and Kellog Caltech data by Langanke and Koonin (see references). 1 After paper on "The Quest for the Origin of the Elements by William A. Fowler, presented in December 1983, when author received the Nobel Prize for Physics. Complete article in Science. 226, 922-935 (November 23. 1984) and in Les Prix Nobel en 1983," Elsevier, New York, 1984]...

FIGURE 5.1 Agraph of atomic radius in picometers (pm) versus atomic number shows a rise-and-fall pattern of periodicity. The maxima occur for atoms of group 1A elements (Li, Na, K, Rb, Cs, Fr) the minima occur for atoms of the group 7A elements. Accurate data are not available for the group 8A elements. 

Mass spectrometry is based on the physical properties of the atomic nucleus. The atomic nucleus of any chemical element consists of protons and neutrons. In an electrically neutral atom the number of positively charged protons in the nucleus equals the number of negatively charged electrons in the shells. The number of protons (Z = atomic number) determines the chemical properties and the place of the element in the periodic table of the elements. The atomic number Z of a chemical element is given as a subscript preceding the elemental symbol (e.g., jH, gC, 17CI, 2eF or 92 )-Besides the protons, uncharged neutrons with nearly the same mass in comparison to the protons (m = 1.67493 x 10 kg versus nip = 1.67262 x 10 kg) stabilize the positive atomic nucleus. In contrast to the mass of the protons and neutrons in the nucleus, the mass of the electrons is relatively small at = 9.10939 x 10 kg. 

Recognition of the fact that elements always displayed the same chemical behavior - regardless of their isotopic composition - led to a reformulation of the periodic law. The idea that each element was characterized by a unique number had already been demonstrated experimentally by Hemy Moseley (1887-1915). By studying the X-ray diffraction patterns produced by a variety of elements, he discovered that the frequencies of the K lines differed from element to element in a predictable and consistent fashion. He went on to show that the frequency of any line in the X-ray spectrum is approximately proportional to A(N-b), where A and b are constants and N is an integer that he termed the atomic number of the element. Moseley was able to identify the number N with the number of protons in the atomic nucleus. Plots of the square root of the frequency for the K and L lines in the X-ray spectra of the elements versus their atomic number, reproduced in Figure 5, show almost straight lines. From this work, it became clear why the order in which certain element pairs appeared in the periodic table needed to be reversed. The pairs in question are argon (39.95) and potassium (39.10) cobalt (58.93) and nickel (58.69) and tellurium (127.60) and iodine (126.91), the... 

Plot the melting points (Table 18.4) of the alkali metals versus atomic number. Predict the melting point for the element francium. Would you predict francium to be a solid or a liquid at room temperature ... 

Making and Using Graphs The densities of the CS group 5A elements are given in the table above. Plot ttU density versus atomic number and state any trends you observe. 

The following ionic radii (in angstroms) are estimated for the +2 ions of selected elements of the first transition-metal series, based on the structures of their oxides Ca (0.99), TP+(0.71), V +(0.64), Mn +(0.80), Fe +(0.75), Co +(0.72), Ni (0.69), Cu (0.71), Zn (0.74). Draw a graph of ionic radius versus atomic number in this series, and account for its shape. The oxides take the rock salt structure. Are these solids better described as high- or low-spin transition-metal complexes ... 

Figure 8.5 Plot of the Ea of the elements versus the atomic number to illustrate the consistency of the electron affinities of a given family and across a period.

Figure 9.3 Bond energies of the homonuclear diatomic anions divided by bond energies of the neutral versus atomic number. The values for the 3d elements are taken from [4]. The 4d and 5d elements are estimated to be the same as for the 3d elements.

Ionization energies measure how tightly electrons are bound to atoms. Ionization always requires energy to remove an electron from the attractive force of the nucleus. Low ionization energies indicate ease of removal of electrons, and hence ease of positive ion (cation) formation. Figure 6-2 shows a plot of first ionization energy versus atomic number for several elements. 

The first equation tells us that helium will not add an electron. The second equation tells us that when one mole of gaseous chlorine atoms gain one electron each to form gaseous chloride ions, 349 kJ of energy is released (exothermic). Figure 6-3 shows a plot of electron affinity versus atomic number for several elements. 

Figure 6-3 A plot of electron affinity versus atomic number for the first 20 elements. The general horizontal trend is that electron affinities become more negative (more energy is released as an extra electron is added) from Group lA through Group VIIA for a given period. Exceptions occur at the IIA and VA elements.

In a plot of first ionization energy versus atomic number for Periods 2 and 3, dips occur at the IIIA and VIA elements. Account for these dips. 

MiniLab 2 Graph density versus atomic mass for the elements in the table above. Describe the relationship between atomic mass and density for the elements. Use your periodic table to locate the elements. Based on these data, what can you say about the trend in density as you move down a column of elements ... 

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