Fluorine ionic bonding

Section 1 2 An ionic bond is the force of electrostatic attraction between two oppo sitely charged ions Atoms at the upper right of the periodic table espe cially fluorine and oxygen tend to gam electrons to form anions Elements toward the left of the periodic table especially metals such as sodium tend to lose electrons to form cations Ionic bonds m which car bon IS the cation or anion are rare... 

Chemists refer to the bond in a molecule like sodium chloride as ionic , meaning that its electron pair resides entirely on chlorine. At the other extreme is the covalent bond in the hydrogen molecule, where the electron pair is shared equally between the two hydrogens. Intermediate cases, such as the bond in hydrogen fluoride which is clearly polarized toward fluorine, are generally referred to as polar covalent bonds (rather than partially ionic bonds). Are these situations really all different or do they instead represent different degrees of the same thing ... 

As opposed to the oxides, fluoride compounds are characterized by the formation of mostly ionic bonds. This peculiarity is related to fluorine s high electronegativity. 

Chemical bonds are classified into two groups transfer of electrons creates an ionic bond while the sharing of electrons leads to a covalent bond. Before studying chemical bonds we need to become familiar with their representation. Chemical bonds may be represented in several ways. We are going to study orbital representation, electron dot representation and line representation. Let s examine these three types using the example of the fluorine molecule, F2. 

Many substances contain bonds that are intermediate in character— between pure covalent and pure ionic bonds. Such polar bonds occur when one of the elements attracts the shared electrons more strongly than the other element. In hydrogen fluoride, for instance, the shared electrons are so much more attracted by fluorine than hydrogen that the sharing is unequal. (See Figure 5-11.)... 

Lewis and many other chemists had recognized the shortcomings of the ionic bond. When diatomic molecules, such as or Cl, were considered, there was no reason why one atom should lose an electron and an identical atom should gain an electron. There had to be another explanation for how diatomic molecules formed. We have seen how the octet rule applies to the formation of ionic compounds by the transfer of electrons. This rule also helps explain the formation of covalent bonds when molecules (covalent compounds) form. Covalent bonds result when atoms share electrons. Using fluorine, F, as a representative halogen, we can see how the octet rule applies to the formation of the molecule. Each fluorine atom has seven valence electrons and needs one more electron to achieve the stable octet valence configuration. If two fluorines share a pair of electrons, then the stable octet configuration is achieved ... 

Potassium (K) transfers its single valence electron to fluorine (F), yielding an ionic bond between K" " and F, as in the following figure ... 

In this case the electropositive sodium atom loses its 3s electron, which is then transferred to the 2p orbital of the electronegative fluorine atom to produce the Na+F ion-pair. Ionic bonding is the subject of Chapter 7. When there is little or no difference in the electronegativity coefficients of the combining atoms, covalent bonds are possible in which two or more electrons are shared between the two atoms. Covalency is the main subject of this chapter. 

The difference in energies between the 3s valence electron of the sodium atom and that of the 2p level in the fluorine atom is so great that the bonding orbital is virtually identical to the 2p(F) orbital, and the anti-bonding orbital is identical to the 3s orbital of the sodium atom. If a bond were formed it would be equivalent to the transfer of an electron from the sodium atom to the fluorine atom, causing the production of the two ions, Na+ and F. A detailed consideration of this specific case is used to explain the nature of ionic bonding. 

This is merely the consequence of smaller atoms having better overbp. The usual prejudice itat fluorine cannot bond covalently arises from the unfortunate tendency to overemphasize the differences between covalent and ionic bonding. Bonding is too often characterized as covalent or ionic, rather than possibly covalent and ionic. 

The covalent bond results when atoms share electrons, as in the formation of the hydrogen molecule. Each hydrogen atom has a single electron thus, by sharing a pair of electrons, two hydrogen atoms can complete their shells of two. Likewise, two fluorine atoms, each with seven electrons in the outer shell, can complete their outer shells by sharing a pair of electrons. As with the ionic bond, the bonding force of the covalent bond is due to electrostatic attraction. However, in the... 

Hydrogen bond-A bond between a hydrogen nuclei and two other entities. One bond is a strong ionic bond (with the donor atom) while the second is a weak covalent bond (frequently shown by a dashed line) with a second structure. The only elements concerned in hydrogen bonding are nitrogen, oxygen, fluorine and sometimes chlorine. 

It has recently been shown that the same principle can be applied to deep eutectic solvents by using small quaternary ammonium cations such as ethylammonium and fluorinated hydrogen bond donors such as trifluoroacetamide. However, there is only a limited benefit that can be achieved using this approach as the physical parameters cannot be varied totally independently of one another. For example there will be an optimum ion size too small and the lattice energy will increase the surface tension, too large and the ionic mobility will be impeded. 

If one atom has a very weak attraction for its valence electron(s) (e.g., sodium, Na), and another atom has a very strong attraction for its valence electrons (e.g., fluorine, F), then the weakly held electron is likely to be stripped away from the first atom by the second atom (fluorine will strip sodium s valence electron). This will usually result in the formation of an ionic bond. If an atom with a weak attraction for its valence electron(s) (e.g., sodium, Na) is around another atom that also has a weak attraction on its valence electron(s) (e.g., Mg), then neither has enough attractive force to take the other s valence electron away. This means that under normal circumstances, these atoms won t react. But if both atoms have strong attractions for electrons, they will attract each other s electrons. The result of this type of atomic tug-of-war generally is that the two atoms will hold on to each other and share electrons. This type of interaction is the basis for a covalent (or molecular) bond. 

Examine Figure 3.11. In an ionic bond, calcium tends to lose two electrons and fluorine tends to gain one electron. Therefore, one calcium atom bonds with two fluorine atoms. Calcium loses one of each of its valence electrons to each fluorine atom. Calcium becomes Ca2+, and fluorine becomes F . They form the compound calcium fluoride, CaF2. 

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