Fourth period

The transition metals, in the center of the periodic table, fill d sublevels. Remember that a d sublevel can hold ten electrons. In the fourth period, the ten elements Sc (Z = 21) through Zn (Z = 30) fill the 3d subleveL In the fifth period, the 4d sublevel is filled by the elements Y (Z = 39) through Cd (Z = 48). The ten transition metals in the sixth period fill the 5d subleveL Elements 103 to 112 in the seventh period are believed to be filling the 6d subleveL... 

You will recall that for fourth period atoms, the 4s sublevel fills before the 3d. In the corresponding ions, the electrons come out of the 4s sublevel before the 3d. This is sometimes referred to as the first in, first out rule. 

To determine the electron configuration in this manner, start with the noble gas of the previous period and use the subshell notation from only the period of the required element. Thus, for Fe, the notation for Ar (the previous noble gas) is included in the square brackets, and the 4s23db is obtained across the fourth period. It is suggested that you do not use this notation until you have mastered the full notation. Also, on examinations, use the full notation unless the question or the instructor indicates that the shortened notation is acceptable. 

Starting at the first electron added to an atom, (a) what is the number of the first electron in the second shell of the atom (b) What is the atomic number of the first element of the second period (c) What is the number of the first electron in the third shell of the atom (d) What is the atomic number of the first element of the third period (e) What is the number of the first electron in the fourth shell of the atom (/) What is the atomic number of the first element of the fourth period ... 

The past fifteen years or so have seen a decided resurgence in theories of aqueous solutions. Although these theories are not the result of any single event, the main components of this final and fourth period can be recognized. 

Scandium is the first element in the fourth period of the transition elements, which means that the number of protons in their nuclei increases across the period. As with all the transition elements, electrons in scandium are added to an incomplete inner shell rather than to the outer valence shell as with most other elements. This characteristic of using electrons in an inner shell results in the number of valence electrons being similar for these transition elements although the transition elements may have different oxidation states. This is also why all the transition elements exhibit similar chemical activity. 

The first ionization energies of the elements are plotted in Figure 1.4. There is a characteristic pattern of the values for the elements Li to Ne which is repeated for the elements Na to Ar, and which is repeated yet again for the elements K, Ca and A1 to Kr (the s- and p-block elements of the fourth period). In the latter case, the pattern is interrupted by the values for the 10 transition elements of the d-block. The fourth period pattern is repeated by the fifth period elements, and there is an additional... 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

The reason for the formation of chemical compounds is therefore essentially the formation of negative ions, and only secondarily that of positive ones. From what has been said, it follows that the elements in the long periods, where they occur more than eight places past a noble gas, can never show normal5 valencies, in the sense that they will lose sufficient electrons to give the structure of the preceding noble gas. After these so-called transition metals there is a series of elements in which the valency rises from one to six, in the fourth period... 

If this assumption is made, many more details of the heat of formation as a function of electron configuration can be readily explained. All examples will be taken from the group of the chlorides see Table XXIII), for which many data on heats of formation are known. However, the statements can be verified in other cases as well. The 3d10 shell is completed in the fourth period from Sc to Ni. In this group the heats of formation of many dichlorides have been measured. 

According to a theory by Pauling, other stable electron configurations can be formed from 3d, 4s and 4p orbitals in the fourth period, and, similarly, of 4d, 5s and 5p in the fifth and 5d, fix and 6p electrons in the sixth period. There is, first of all, a configuration in which eight electrons are involved, 2d, 2s and 4p electrons that form four stable bonds. This configuration is called... 

Were these your answers There are nine orbitals in the fourth shell. In order of increasing energy level, they are the one 45 orbital, the five 3d orbitals, and the three 4p orbitals. Because each orbital can hold two electrons, the total electron capacity of the fourth shell is 2 x 9 = 18 electrons, which is the same number of elements found in the fourth period of the periodic table. 

According to Fig. 1.33, electrons occupy 4p-orbitals once the 3d-orbitals are full. The configuration of germanium, [Ar]3d104s24p2, for example, is obtained by adding two electrons to the 4p-orbitals outside the completed 3d-subshell. The fourth period of the table contains 18 elements, because the 4s- and 4p-orbitals can accommodate a total of 8 electrons and the 3d-orbitals can accommodate 10. Period 4 is the first long period of the periodic table. 

In table I, the systems of regularities now known for arc and spark spectra of ten elements in the fourth period are represented, the numbers, 1,2,3, 4, etc., indicating the maximum multiplicities in the spectral terms or atomic energy levels. 

Systems of Spectral Structures for Ten Elements of the Fourth Period (a) Arc Spectra, Neutral Atoms... 

Horizontal rows of elements in the periodic table are called periods, the first of which consists of only hydrogen (H) and helium (He). The second period begins with atomic number 3 (lithium) and terminates with atomic number 10 (neon), whereas the third goes from atomic number 11 (sodium) through atomic number 18 (argon). The fourth period includes the first row of transition elements, whereas lanthanides and actinides, which occur in the sixth and seventh periods, respectively, are fisted separately at the bottom of the table. 

HELCOM (2001) Fourth Periodic Assessment of the State of the Baltic Marine Area, 1994-1998 Baltic Sea Environment Proceedings No. 82, Helsinki. 

The electrical behaviour of some oxides of transition metals (belonging to fourth period) is given in following table. It may be noted that these oxides show wide variation in their electrical behaviour. 

Octet expansion or hypervalent state is due to the involvement of d-orbitals of the same principal quantum shell (e.g., 3d in third period, 4d in fourth period, etc.). The two other factors that play a role in octet expansion are ... 

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