Periodic Trends in Properties of Elements

Although all the electrons in an atom shield one another to some extent, those that are most effective at shielding are the core electrons. As a result, the value of Zgff increases steadily from left to right across a period of the periodic table because the number of core electrons remains the same (only the number of protons, Z, and the number of valence electrons increases). 

As we move to the right across period 2, the nuclear charge increases by 1 with each new element, but the effective nuclear charge increases only by an average of 0.64. (If the valence electrons did not shield one another, the effective nuclear charge would also increase by 1 each time a proton was added to the nucleus.) 

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Effective Nuclear Charge Periodic Trends in Properties of Elements... 

The periodic trend of a decrease in atomic radii across a period is readily seen in the Figure 6.4. Other properties related to atomic radii show a similar pattern. Knowing that the elements exhibit a general periodic trend allows us to predict unknown properties for elements and aided in the discovery of unknown elements. The periodic nature of the elements supported the development of the quantum theory. The elements show a periodic pattern in both their properties and electron configurations. The periodic trend in properties of the elements... 

Many of the periodic trends in properties of the elements can be explained using Coulomb s law, which states that the force (F) between two charged objects (Qi and is directly proportional to the product of the two charges and inversely proportional to the distance (d) between the objects squared Force is inversely proportional to d, whereas energy is inversely proportional to d [W Section 5.1]. The SI unit of force is the newton (N = m kg/s ) and the SI unit of energy is the joule (J = m kg/s"). 

The periodic trends in main-group elements become apparent when we compare the binary compounds they form with one specific element. All the main-group elements, with the exception of the noble gases and, possibly, indium and thallium, form binary compounds with hydrogen, so these hydrides can be examined to look for periodic trends. We meet the binary hydrides several times in this chapter and the next, so, at this stage, we confine the discussion to a brief survey and see how their properties reveal periodic behavior. 

The oxides of main-group elements show periodic trends in properties. Oxides of metals tend to be ionic and to form basic solutions in water. Oxides of nonmetals are molecular and the anhydrides of acids. 

Understanding a trend among the elements enables you to make predictions about the chemical behavior of the elements. These trends in properties of the elements in a group or period can be explained in terms of electron configurations. 

Across a period, the elements become less metallic and more nonmetallic with corresponding changes in chemical properties. The arrangement of the elements in the periodic table makes it easier to see trends in their properties within groups and across periods. Two important properties of elements are the size of their atoms and the ease (or lack of ease) with which they lose an electron. Both are functions of the periodic similarities of electronic configuration, causing both size and ease of electron loss to be periodic properties of the elements. 

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. ... 

Atomic radii, ionization energies, and electron affinities are properties of individual atoms. With the exception of the noble gases, however, none of the elements exist in nature as individual atoms. To get a broader understanding of the properties of elements, we must also examine periodic trends in properties that involve large collections of atoms. 

Chemists in the nineteenth century recognized periodic trends in the physical and chemical properties of elements, long before quantum theory came onto the scene. Although these chemists were not aware of the existence of electrons and protons, their efforts to systematize the chemistry of the elements were remarkably successful. Their main sources of information were the atomic masses of the elements and other known physical and chemical properties. Modem quantum theory allows us to understand these periodic trends in terms of the ways in which the electrons are distributed among the atomic orbitals of an atom. 

Figure 22.1 Trends in properties of the elements as a function of position in the periodic table. 

Chemical and physical properties of elements follow trends within the periodic table. These trends are described in terms of changes in properties of elements from the top to the bottom of groups, and from the left to the right of periods. The sizes of atoms and first ionization energies are two properties that show distinct trends. 

There are similar, but smaller, trends in the properties of elements in a column (a family) of the periodic table. Though the elements in a family display similar chemistry, there are important and interesting differences as well. Many of these differences are explainable in terms of atomic size. 

The periodic table is an arrangement of the elements that reflects their family relationships members of the same group typically show a smooth trend in properties. 

This chapter and the following two chapters survey the properties of the elements and their compounds in relation to their locations in the periodic table. To prepare for this journey through the periodic table, we first review the trends in properties discussed in earlier chapters. We then start the journey itself with the unique element hydrogen and move on to the elements of the main groups, working from left to right across the table. The same principles apply to the elements of the d and f blocks, but these elements have some unique characteristics (mainly their wide variety of oxidation states and their ability to act as Lewis acids), and so they are treated separately in Chapter 16. 

Predict and explain periodic trends in the properties of the elements in Groups 15/V through 18/VIII. 

C noting periodic trends in the properties of known elements that surrounded the blank spaces in the periodic table... 

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. 

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