Lithium valence electrons

Some excited configurations of the lithium atom, involving promotion of only the valence electron, are given in Table 7.4, which also lists the states arising from these configurations. Similar states can easily be derived for other alkali metals. 

Because each lithium atom has one valence electron and each molecular orbital can hold two electrons, it follows that the lower half of the valence band (shown in color in Figure 5) is filled with electrons. The upper half of the band is empty. Electrons near the top of the filled MOs can readily jump to empty MOs only an infinitesimal distance above them. This is what happens when an electrical field is applied to the crystal the movement of electrons through delocalized MOs accounts for the electrical conductivity of lithium metal. 

There is little new to be said about the bonding capacity of a lithium atom. With just one valence electron, it should form gaseous molecules LiH and LiF. Because of the vacant valence orbitals, these substances will be expected only at extremely high temperatures. These expectations are in accord with the facts, as shown in Table 16-1, which summarizes the formulas and the melting and boiling points of the stable fluorides of the second-row elements. In each case, the formula given in the table is the actual molecular formula of the species found in the gas phase. 

As we have mentioned earlier, lithium has one valence electron, hence can share a pair of electrons with one fluorine atom ... 

Consider a crystal of metallic lithium. In its crystal lattice, each lithium atom finds around itself eight nearest neighbors. Yet this atom has only one valence electron, so it isn t possible for it to form ordinary electron pair bonds to all of these nearby atoms. However, it does have four valence orbitals available so its electron and the valence electrons of its neighbors can approach quite close to its nucleus. Thus each lithium atom has an abundance of valence orbitals but a shortage of bonding electrons. 

Consider the dilemma of the valence electron of a particular lithium atom. It finds eight neigh-... 

Ionization lithium, 267 magnesium, 270 sodium, 270 Ionization energy, 267 alkaline earths, 379 and atomic number, 268 and ihe periodic table, 267 and valence electrons, 269 halogens, 353 measurement of, 268 successive, 269 table of, 268 trends, 268... 

The element with Z = 4 is beryllium (Be), with four electrons. The first three electrons form the configuration ls22s1, like lithium. The fourth electron pairs with the 2s-electron, giving the configuration ls22s2, or more simply [He 2s2 (41. A beryllium atom therefore has a heliumlike core surrounded by a valence shell of two paired electrons. Like lithium—and for the same reason—a Be atom can lose only its valence electrons in chemical reactions. Thus, it loses both 2s-electrons to form a Be2+ ion. 

Lithium has been alloyed with gaUium and small amounts of valence-electron poorer elements Cu, Ag, Zn and Cd. like the early p-block elements (especially group 13), these elements are icosogen, a term which was coined by King for elements that can form icosahedron-based clusters [24]. In these combinations, the valence electron concentrations are reduced to such a degree that low-coordinated Ga atoms are no longer present, and icosahedral clustering prevails [25]. Periodic 3-D networks are formed from an icosahedron kernel and the icosahedral symmetry is extended within the boundary of a few shells. 

C is a universal constant (calculable from the model) and r is the density parameter equal to r = (3/4 7T)1/3 (V[N t )J,/3 V is the volume of the unit cell which contains Adatoms, and each atom contributes v free valence electrons to the collective motion. Because the actual crystal structure is disregarded, only one value of 7 is obtained for each metal. For lithium, for instance, 7 seems to be 490 erg/cm2 and... 

In general, for groups, when the table is read from left to right, the number of valence electrons in the outer shell of elements increases. For instance, lithium is located at the start of period 2 and has one electron in its outer shell and is found in group 1 (lA), and neon, located at the end of period 2 in group 18 (VIIIA), has eight electrons in its completed outer shell. 

All of the alkali metals are electropositive and have an oxidation state of 1 and form cations (positively charged ions) by either giving up or sharing their single valence electron. The other elements of group 1 are lithium (jLi), sodium (jjNa), potassium (j K), rubidium (j Rb), cesium (jjCs), and francium (g Fr). Following are some characteristics of the group 1 alkali metals ... 

In the metallic state, lithium is a very soft metal with a density of 0.534 g/cm. When a small piece is placed on water, it will float as it reacts with the water, releasing hydrogen gas. Lithium s melting point is 179°C, and it has about the same heat capacity as water, with a boiling point of 1,342°C. It is electropositive with an oxidation state of + 1, and it is an excellent conductor of heat and electricity. Its atom is the smallest of the alkali earth metals and thus is the least reactive because its valence electron is in the K shell, which is held closest to its nuclei. 

Because its outet valence electrons ate at a gteatet distance from its nuclei, potassium is more reactive than sodium or lithium. Even so, potassium and sodium are very similar in their chemical reactions. Due to potassiums high reactivity, it combines with many elements, particularly nonmetals. Like the other alkali metals in group 1, potassium is highly alkaline (caustic) with a relatively high pH value. When given the flame test, it produces a violet color. 

Two lithium atoms each transfer a single electron to one sulfur atom to yield the ionic compound U2S. As an alkali metal (Group lA), lithium easily gives up its single valence electron. As a Group VIA nonmetal, sulfur readily accepts two additional electrons into its valence shell. 

With such high coordination numbers it is quite clear that there can be no possibility of covalency, because there are insufficient numbers of electrons. The difficulty is shown in the case of metallic lithium, with its body-centred cubic structure and coordination number of 14. Each lithium atom has one valency electron and for each atom to participate in 14 covalent bonds is quite impossible. 

The pronounced tendency of the lithium atom to form intramolecular bonding can be explained by its possessing only Is completed shell and by its valence electron ability to move to the p-orbit (2s 2p), it being possible for the lithium arum to make use of the... 

Hydrogen, lithium and other intramolecular bonds or intermolecular ones are by their origin secondary chemical bonds. Strong chemical bonds result from a primary act of interaction of atoms, whereas weak chemical bonds appear as a result of alteration in their valence states on condition that the energy content of valence electrons of those atoms can provide for the formation of new chemical bonds. 

If light is passed through lithium vapor containing lithium atoms in the normal state, with the valence electron in the 2s orbital, the only... 

A characteristic feature of the structuie of most electron-deficient substances is that the atoms have ligancy that is not only greater than the number of valence electrons but is even greater than the number of stable orbitals.66 Thus most of the boron atoms in the tetragonal form of crystalline boron have ligancy 6. Also, lithium and beryllium, with four stable orbitals and only one and two valence electrons, respectively, have structures in which the atoms have ligancy 8 or 12. All metals can be considered to be electron-deficient substances (Chap. 11). 

For most atoms there wilt be a maximum of eight electrons in the valence shell (- Lewis octet structure). This is absolutely necessary for atoms of the elements lithium through fluorine since they have only four orbitals (an s and three p orbitals) in the valence shell. It is quite common, as well, for atoms of other elements to utilize only their s and p orbitals. Under these conditions the sum of shared pairs (bonds) and unshared pairs (lone pairs) must equal the number of orbitals—four. This is the maximum, and for elements having fewer than four valence electrons, the octet will usually not be filled. The following compounds illustrate these possibilities ... 

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