Quantum level, principal

The following properties are observed for an unknown element. Identify the element from its properties, (a) The neutral atom has two unpaired electrons, (b) One of the valence electrons in the ground state atom has mt = 4 I. (c) The most common oxidation state is +4. (d) If an electron in a hydrogen atom were excited to the same principal quantum level, n, as the valence electrons in an atom of this element, and fell to the n — 1 quantum level, the photon emitted would have an energy of 4.9 X 10—20 J. 

A Removing an electron from Li2 removes a bonding electron because the valence molecular orbital diagram for Li2 is the same as that for H2, only it is just moved up a principal quantum level aub[U o,/ o2ib[U o2i Q. The molecular orbital diagram for Li2+ is ... 

For principal quantum level n = 5, determine the number of subshells (different values of ) and give the designation of each. 

There are no d orbitals that correspond to principal quantum levels n — and n = 2. The d orbitals ( = 2) first occur in level n = 3. The five 3d orbitals have the shapes shown in Fig. 12.21. The d orbitals have two different fundamental shapes. Four of the orbitals (dxz, dyz, dxy, and dxi-yi) have four lobes centered in the plane indicated in the orbital label. Note that dxy and dx2-yi are both centered in the xy plane the lobes of lie along the x and... 

At this point it is useful to introduce the concept of valence electrons, the electrons in the outermost principal quantum level of an atom. The valence electrons of the nitrogen atom, for example, are the 2s and 2p electrons. For the sodium atom the valence electron is the electron in the 3s orbital, and so on. Valence electrons are the most important electrons to chemists, because they are involved in bonding, as we will see in the next two chapters. The inner electrons are known as core electrons. 

Electrons in the same principal quantum level do not shield each other as well as core electrons shield outer electrons. 

Atomic radius increases down a group, because of the increases in the orbital sizes in successive principal quantum levels. 

An excited hydrogen atom emits light with a wavelength of 397.2 nm to reach the energy level for which n = 2. In which principal quantum level did the electron begin ... 

Core electron an inner electron in an atom one not in the outermost (valence) principal quantum level. (12.13) Corrosion the process by which metals are oxidized in the atmosphere. (11.6)... 

Valence electrons the electrons in the outermost principal quantum level of an atom. (12.13)... 

As each orbital may contain a maximum of two electrons, the helium atom has a full complement at Is2, as does the hydrogen anion. There is only one subshell in the first principal quantum level, and so there can only be two elements that have electrons only in this level. That is why there are only two first row elements of the Periodic Table. 

This is why there are eight second row elements. It is possible to add an electron to, or remove electrons from, an orbital that is not within the highest principal quantum level that is normally occupied in the neutral atom. However, this requires a lot of energy and so only occurs very rarely. Write down the electronic configuration of the mononegative anion of helium, and so suggest why this species is not readily formed. 

The electron that was added to the helium atom to form the anion could not fit into the s subshell of the first principal quantum shell, because it already had two electrons and so was full. Instead, this extra electron occupied the next available orbital, which was the s subshell of the second principal quantum level. This requires a lot of energy, and so it is difficult. Hence, the He- anion, which it should also be noted is a radical species, is not normally found. 

The second row elements, lithium to neon, sequentially fill the available four subshells in the second principal quantum level, starting with the s subshell and then progressing to the three p subshells. The latter three each have the same... 

As the loss or gain of electrons normally only occurs from the highest principal quantum level that is occupied in the atom, it is this level that is concerned with the chemistry of the element. 

Accordingly, the highest principal quantum level that is normally occupied in the neutral atom is called the valence shell, the name of which reflects its involvement in the chemistry of the atom. Usually only the electrons within the valence shell are indicated, and the electrons within the core shells are assumed to be in order. 

It is difficult to form certain ions of the second row elements, e.g. Ne, F and Li, because in each case it would be necessary either to remove (in the case of lithium), or to add (in the case of neon and fluorine) an electron from, or to, a different principal quantum level than the one in which the outermost electrons of the neutral atom were accommodated. 

As each element in the second row has four subshells in the second principal quantum level, and as each subshell may only accommodate a maximum of two electrons, the result is that no element in the second row may have more than eight electrons in the second principal quantum shell. This is called the Octet rule, and is one of the most fundamental rules concerning the electron distribution around second row elements. Under normal conditions, it is never violated. 

One especially important difference between polyelectronic atoms and the hydrogen atom is that for hydrogen all the orbitals in a given principal quantum level have the same energy (they are said to be degenerate). This is not the case for polyelectronic atoms, where we find that for a given principal quantum level the orbitals vary in energy as follows ... 

The same thing happens in the other principal quantum levels as well. Figure 7.22 shows the radial probability profiles for the Zs, 3p, and 3d orbitals. Note again the hump in the 3s profile very near the nucleus. The innermost hump for the 3p is farther out, which causes the energy of the 35 orbital to be lower than that of the 3p. Notice that the 3d orbital has its maximum probability closer to the nucleus than either the 3s or 3p does, but its absence of probability near the nucleus causes it to be highest in energy of the three orbitals. The relative energies of the orbitals for = 3 are... 

An excited hydrogen atom with an electron in the = 5 state emits light having a frequency of 6.90 X 10 s. Determine the principal quantum level for the final state in this electronic transition. 

The valence orbitals are the orbitals associated with the highest principal quantum level that contains electrons on a given atom. 

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