Periodic table first rows

In the modern periodic table, horizontal rows are known as periods, and are labeled with Arabic numerals. These correspond to the principal quantum numbers described in the previous section. Because the outer shells of the elements H and He are 5 rather than p orbitals, these elements are usually considered differently from those in the rest of the table, and thus the 1st period consists of the elements Li, Be, B, C, N, O, F, and Ne, and the 2nd Na to Ar. Periods 1 and 2 are known as short periods, because they contain only eight elements. From the discussion above, it can be seen that these periods correspond to the filling of the p orbitals (the 2p levels for the first period, and the 3p for the second), and they are consequently referred to as p-block elements. The 3rd and 4th periods are extended by an additional series of elements inserted after the second member of the period (Ca and Sr respectively), consisting of an extra ten elements (Sc to Zn in period 3 and Y... 

The modern periodic table first appeared as a page for a chemistry textbook, written by a teacher who thought his students needed an easy way to look at the elements. The shape of the table made it world-famous, for all the reasons mentioned. The carefully stacked rows and columns made a simple list into a useful tool and a snapshot of how matter is organized on Earth and throughout the universe. 

M-H bond strengths increase from first to second to third row in the periodic table first < second < third row. The introduction of electron-donating substituents (i.e., the replacement of a carbonyl by a phosphine or phosphite) has little effect on the M-H bond strength, as the effect on the pX largely cancels that on the oxidation potential. - ... 

However, the situation is quite different when the N or F centers are replaced with atoms below them in the periodic table. First considering substitution of one of these atoms by its second-row analogue, the MP2 value of R(N Cl) in H3N HCl... 

The period (or row) of the periodic table m which an element appears corresponds to the principal quantum number of the highest numbered occupied orbital (n = 1 m the case of hydrogen and helium) Hydrogen and helium are first row elements lithium in = 2) IS a second row element... 

In Figure 8.1(c) the higher-energy orbitals are indicated as being valence orbitals but, in most applications of AES, they are core orbitals. For this reason the technique is not usually concerned with atoms in the first row of the periodic table. 

Ground-state electronic configuration is ls 2s 2p 3s 3p 3i 4s. Manganese compounds are known to exist in oxidation states ranging from —3 to +7 (Table 2). Both the lower and higher oxidation states are stabilized by complex formation. In its lower valence, manganese resembles its first row neighbors chromium and especially iron ia the Periodic Table. Commercially the most important valances are Mn, Mn ", or Mn ". ... 

Nickel occurs in the first transition row in Group 10 (VIIIB) of the Periodic Table. Some physical properties are given in Table 1 (1 4). Nickel is a high melting point element having a ductile crystal stmcture. Its chemical properties allow it to be combined with other elements to form many alloys. 

Some large basis sets specify different sets of polarization functions for heavy atoms depending upon the row of the periodic table in which they are located. For example, the 6-311+(3df,2df,p) basis set places 3 d functions and 1 f function on heavy atoms in the second and higher rows of the periodic table, and it places 2 d functions and 1 f function on first row heavy atoms and 1 p function on hydrogen atoms. Note that quantum chemists ignore H and Ffe when numbering the rows of the periodic table. 

The first step in reducing the computational problem is to consider only the valence electrons explicitly, the core electrons are accounted for by reducing the nuclear charge or introducing functions to model the combined repulsion due to the nuclei and core electrons. Furthermore, only a minimum basis set (the minimum number of functions necessary for accommodating the electrons in the neutral atom) is used for the valence electrons. Hydrogen thus has one basis function, and all atoms in the second and third rows of the periodic table have four basis functions (one s- and one set of p-orbitals, pj, , Pj, and Pj). The large majority of semi-empirical methods to date use only s- and p-functions, and the basis functions are taken to be Slater type orbitals (see Chapter 5), i.e. exponential functions. 

The horizontal rows in the table are referred to as periods. The first period consists of the two elements hydrogen (H) and helium (He). The second period starts with lithium (Li) and ends with neon (Ne). 

Potassium has one valence electron. It is the first member of the fourth row, the row based on the cluster of orbitals with about the same energy as the 45 orbital. There are nine such orbitals, tne 4s orbital, the three 4p orbitals, and the five 3d orbitals. Hence the fourth row of the periodic table will differ from the second and third rows. The fourth row, as seen in the periodic table, consists of eighteen elements. 

Just as the long fourth row of the periodic table arises from filling the 4s, 3d, and Ap orbitals, the fifth row, which also consists of eighteen elements, comes from filling the 5s, Ad, and 5p orbitals. In the sixth row, something new happens. After the 6s and the first one of the 5d electrons have entered, subsequent electrons go into the 4/orbitals. The fact that there are seven 4/ orbitals means that fourteen electrons can be accommodated in this manner. Filling the Af orbitals gives rise to a series of elements with almost identical chemical properties called the rare earth... 

But I want to return to my claim that quantum mechanics does not really explain the fact that the third row contains 18 elements to take one example. The development of the first of the period from potassium to krypton is not due to the successive filling of 3s, 3p and 3d electrons but due to the filling of 4s, 3d and 4p. It just so happens that both of these sets of orbitals are filled by a total of 18 electrons. This coincidence is what gives the common explanation its apparent credence in this and later periods of the periodic table. As a consequence the explanation for the form of the periodic system in terms of how the quantum numbers are related is semi-empirical, since the order of orbital filling is obtained form experimental data. This is really the essence of Lowdin s quoted remark about the (n + , n) rule. 

Alternatively any triads taken from combinations of elements in rows 2, 3, 4 or 4, 5, 6 and so on, do not give perfect triads. The reason why this works so perfectly, albeit in only about 50% of possible triads, is because the length of each period repeats just once in the long-form periodic table, with the exception of the very first short period. The full sequence is 2, 8, 8, 18, 18, 32, presumably 32, and so forth. 

The transition elements comprise groups 3 to 12 and are found in the central region of the standard periodic table, an example of which is reproduced on the endpaper. This group is further subdivided into those of the first row (the elements scandium to zinc), the second row (the elements yttrium to cadmium) and the third row (the elements lanthanum to mercury). The term transition arises from the elements supposed transitional positions between the metallic elements of groups 1 and 2 and the predominantly non-metallic elements of groups 13 to 18. Nevertheless, the transition elements are also, and interchangeably, known as the transition metals in view of their typical metallic properties. 

Let us first briefly review the construction of molecular orbitals in simple diatomic molecules, AB, using the linear combination of atomic orbitals (LCAO) scheme. The end product for the first long row of the periodic table is the well-known diagram in Fig. 6-1. We focus on two broad principles that are exploited in the construction of this diagram one has to do with symmetry and overlap, the other concerns energies. 

In the Brpnsted picture, the acid is a proton donor, but in the Lewis picture the proton itself is the acid since it has a vacant orbital. A Brpnsted acid becomes, in the Lewis picture, the compound that gives up the actual acid. The advantage of Lewis theory is that it correlates the behavior of many more processes. For example, AICI3 and BF3 are Lewis acids because they have only 6 electrons in the outer shell and have room for 8. Both SnCU and SO3 have eight, but their central elements, not being in the first row of the periodic table, have room for 10 or 12. Other Lewis acids are simple cations, like Ag. The simple reaction A + B- A—B is not very common in organic chemistry, but the scope of the Lewis picture is much larger because reactions of the types... 

If we limit ourselves to the first row of the periodic table, B can only be nitrogen, C can be carbon or nitrogen, and A can be carbon, oxygen, or... 

In practice one can differentiate between two kinds of donors, the resulting donor-acceptor bonds can be largely ionic (class I) or covalent (class II) [16]. Donors of the first type (class I) stem from the first row of the periodic table of elements, such as amines, ethers, in detail structures in which the Lewis basis centre possessing the non-bonding lone pair is strong electronegative. Donors of the second type are constituted from elements of the second row of the periodic table of elements, such as phosphines, thioethers, etc. (class II). These Lewis donors are... 

The description of the first 10 electrons in the configuration of aluminum is identical to that of neon, so we can represent that portion as [Ne]. With this notation, the configuration of A1 becomes [Ne] 3 5" 3 p The element at the end of each row of the periodic table has a noble gas configuration. These configurations can be written in the following shorthand notation ... 

First ionization energy increases from left to right across each row and decreases from top to bottom of each column of the periodic table. 

Elements beyond the second row of the periodic table can form bonds to more than four ligands and can be associated with more than an octet of electrons. These features are possible for two reasons. First, elements with > 2 have atomic radii that are large enough to bond to 5, 6, or even more ligands. Second, elements with > 2 have d orbitals whose energies are close to the energies of the valence p orbitals. An orbital overlap description of the bonding in these species relies on the participation of d orbitals of the inner atom. 

The densities of transition metals also display regular periodic trends, as Figure 20-2b shows. Density increases moving down each column of the periodic table and increases smoothly across the first part of each row. 

The first ionization energies of transition metals show gradual upward trends across each row of the periodic table. 

The preceding discussion applies only to structural units in which the chain atoms consist principally of carbon or other similarly bonded elements from the first row of the periodic table. The greater bond lengths and modified bond angles for larger atoms lead to rather different circumstances. In the cyclodimethylsiloxane series... 

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