Physical properties, periodic trends

The trends in chemical and physical properties of the elements described beautifully in the periodic table and the ability of early spectroscopists to fit atomic line spectra by simple mathematical formulas and to interpret atomic electronic states in terms of empirical quantum numbers provide compelling evidence that some relatively simple framework must exist for understanding the electronic structures of all atoms. The great predictive power of the concept of atomic valence further suggests that molecular electronic structure should be understandable in terms of those of the constituent atoms. 

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. 

The physical and chemical properties of the elements show regular periodic trends that can be explained using electron configurations and nuclear charges. We focus on the physical properties of the elements in this section. A preliminary discussion of the chemical properties of some of the elements appears in Section Other chemical properties are discussed after we introduce the principles of chemical bonding in Chapters 9 and 10. 

It is important to be familiar with periodic trends in physical and chemical properties, but it is just as important to understand the principles that give rise to these trends. Example shows how to analyze trends in terms of the underlying principles. 

The periodic table organizes a remarkable amount of information about the chemical and physical properties of the elements. The information is organized in such a manner that trends in properties and important relationships can be readily identified. In this activity, you will identify several elements based on their properties and the properties of the surrounding elements in the periodic table. 

Two chemists in attendance at the Karlsruhe were Julius Lothar Meyer (1830-1895) and Dmitri Mendeleev (1834-1907). These two independently developed the periodic law and constructed their own versions of the periodic table. Meyer based his table primarily on the physical properties of the elements. Meyer plotted atomic volume against the atomic mass and noticed the periodicity in volumes of the elements. Other physical properties also showed periodic trends. Figure 6.2 shows how the melting point of the first fifty-five elements rises and falls in a roughly periodic fashion as atomic number increases. Based on his analysis, Meyer published his periodic table in 1870. 

R. J. Puddephatt and P. K. Monaghan, The Periodic Table of the Elements, 2nd edn., Oxford University Press, Oxford, 1986. A concise description of the structure of the Periodic Table and a discussion of periodic trends of many physical and chemical properties of the elements. 

In other words, state what you think happens to the acid-base properties of oxides as you go across a period and down a group. Make a quick sketch of the periodic table to illustrate this trend. Flow would you describe the acid-base properties of the metalloids (Use your knowledge of the physical properties of the metalloids to help you make your inference.)... 

Periodic trends and the chemical and physical properties of the elements... 

The immense number of chemical compounds formed by the halogens provides chemists with an extraordinary database from which numerous chemical and physical phenomena can be correlated with respect to various periodic trends. From databases like Inorganic Crystal Structure Data (ICSD, http //www.fiz-karlsruhe.de ) and International Centre for Diffraction Data (ICDD, http //www.icdd.com) with 67 000 and 25 000 entries, respectively, one can easily make out that halides are one of the dominant classes of compounds besides oxides. Even within the subset of inorganic solids, there is tremendous diversity of composition, stracture, and properties and to summarize this would create its own encyclopedia. Therefore, the discussion in this article is limited primarily to binary halides, their structures, and some of their properties, except halides of elements which are nonmetals. Binary actinide hahdes are discnssed elsewhere see Actinides Inorganic Coordination Chemistry). Complex hahdes (sohd phases containing two or more kinds of metal ions), ... 

Let s begin by surveying some of the key physical and chemical properties of the transition-metal elements and interpreting trends in those properties using the quantum theory of atomic structure developed in Chapter 5. We focus initially on the fourth-period elements, also called the first transition series (those from scandium through zinc in which the 3d shell is progressively filled). Then we discuss the periodic trends in the melting points and atomic radii of the second and third transition series elements. 

Table 8.1 lists some key physical properties of the elements of the first transition series, taken mostly from Appendix F. The general trends in all of these properties can be understood by recalling that nuclear charge also increases across a period as electrons are being added to the same subshell, in this case, the d shell. The first and second ionization energies tend to increase across the period, but not smoothly. The energies of the 4s and 3d orbitals are so close to one another that the electron configurations of the neutral atoms and their ions are not easily predicted from the simplest model of atomic structure. 

The periodic table has been described as the chemist s best friend. Chemical reactions involve loss, gain, or sharing of electrons. In this chapter, we have seen that the fundamental basis of the periodic table is that it reflects similarities and trends in electron configurations. It is easy to use the periodic table to determine many important aspects of electron configurations of atoms. Practice until you can use the periodic table with confidence to answer many questions about electron configurations. As we continue our study, we will learn many other useful ways to interpret the periodic table. We should always keep in mind that the many trends in chemical and physical properties that we correlate with the periodic table are ultimately based on the trends in electron configurations. 

It is not necessary to learn the numerical values of the various physical properties, but the trends that they follow from left to right and from the top to the bottom of the Periodic Table are important. Thus, it is useful information that with the exception of H and He, fluorine, F (64 pm), is the smallest element and potassium, K (227 pm) is the largest element in the first 18 elements of the Periodic Table. These three physical properties are clearly determined by the electron configurations of the elements and their positions in the Periodic Table. It is just this combination of these three physical properties that is responsible for the chemical properties of the elements. 

After Dalton, there were several attempts throughout Western Europe to organize the known elements into a conceptual framework that would account for the similar properties that related groups of elements exhibit and for trends in properties that correlate with increases in atomic weights. The most successful periodic table of the elements was designed in 1869 by a Russian chemist, Dmitri Mendeleev. Mendeleev s method of organizing the elements into columns grouping elements with similar chemical and physical properties proved to be so practical that his table is still essentially the only one in use today. 

When the Russian chemist Dmitri Mendeleev (1834-1907) developed his version of the periodic table in 1869, he arranged the elements known at that time in order of atomic mass or atomic weight so that they fell into columns called groups or families consisting of elements with similar chemical and physical properties. By doing so, the rows exhibit periodic trends in properties going from left to right across the table, hence the reference to rows as periods and name periodic table. ... 

All of the elements in the first 12 groups of the periodic table are referred to as metals. The first two groups of elements on the left-hand side of the table are the alkali metals and the alkaline earth metals. All of the alkali metals are extremely similar to each other in their chemical and physical properties, as, in turn, are all of the alkaline earths to each other. The 10 groups of elements in the middle of the periodic table are transition metals. The similarities in these groups are not as strong as those in the first two groups, but still satisfy the general trend of similar chemical and physical properties. The transition metals in the last row are not found in nature but have been synthesized artificially. The metals that follow the transition metals are called posttransition metals. 

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