Cation from nonmetal atoms

Cations are generally metallic radicals obtained by loss of electrons from metal atoms (M (metal) — M + (cation) + ne (electrons)), while anions are nonmetallic ions or radicals (a group of atoms of two or more elements) obtained by the acquisition of electrons by nonmetallic atoms (A (nonmetal) + me —> Am (anion). 

Ionic bonding involves the transfer of electrons from one atom to another. The more electronegative element gains electrons. The less electronegative element loses electrons. This results in the formation of cations and anions. Usually, an ionic bond forms between a metal and a nonmetal. The metal loses electrons to form a cation. The nonmetal gains electrons to become an anion. The attraction of the opposite charges forms an ionic solid. 

FIGURE 2.1 Considerable energy is needed to produce cations and anions from neutral atoms the ionization energy of the metal atoms must be supplied, and it is only partly recovered from the electron affinity of the nonmetal atoms. The overall lowering of energy that drags the ionic solid into existence is due to the strong attraction between cations and anions that occurs in the solid. 

To work out the formula of an ionic compound using Lewis symbols, we first represent the cation by removing the dots from the symbol for the metal atom. Then we represent the anion by transferring those dots to the Lewis symbol for the nonmetal atom to complete its valence shell. We may need to adjust the numbers of atoms of each kind so that all the dots removed from the metal atom symbols are accommodated by the nonmetal atom symbols. Finally, we write the charge of each ion as a superscript in the normal way. A simple example is the formula of potassium chloride ... 

Nonmetal atoms accept electrons from metal atoms if the metal atoms are available, or else they share electrons they never donate electrons to form monatomic cations. The largest charge on any monatomic cation is 4 -I-, and on any monatomic anion, it is 3 —. 

In the previous section, the ionic bond and the reaction of metals with nonmetals to form ionic compounds were discussed. In this section, we examine the nature of the bond between atoms of two nonmetals, those elements to the right of the stair step on the periodic table. You will recall that in reactions between metals and nonmetals, metals lose electrons to form cations and nonmetals acquire them to from anions. But what if both elements are nonmetals Nonmetals, like O, Br, or N, do not lose electrons easily if anything, they prefer to acquire them. As a result, when two nonmetals bond to one another, they do so by sharing electrons forming bonds described as covalent. A covalent bond is a pair of electrons shared by two atoms. Compounds that are held together by covalent bonds are called covalent compounds, and they exist as individual molecules. Covalent bonding provides a second way for atoms to acquire an octet of electrons in their valence shells. The pair of electrons shared by two atoms becomes part of the valence shell of both atoms. 

Finally, ionic bonds are formed between elements from opposite sides of the periodic table (typically between a metal and a nonmetal), where there is a large difference in electronegativity between the atoms. Because metals have very low lEs and nonmetals have large EAs, an ionic bond is characterized by the transfer of one or more electrons from one atom to another to form a cation-anion pair. As a general rule, the nondirectional nature of the electrostatic attraction between the ions leads to fairly high melting and boiling points. Most ionic solids are insulators because the ions are fixed in place in the crystalline lattice however, they become electrical conductors when molten or dissolved in aqueous solution. 

In effect, the metal atoms transfer electrons to the nonmetal atoms. The resulting large numbers of cations and anions attract each other and form the ionic compound. A cation or anion derived from a single atom is called a monatomic ion we ll discuss polyatomic ions, those derived from a small group of atoms, later. 

Nonmetal atoms have too many valence electrons to lose them all and become cations, so an anion and a cation cannot both come from two nonmetal atoms. By sharing electrons, however, they form covalent bonds in which each atom reaches a noble-gas structure. The compounds formed in this way are molecular. Conclusion The bond between two nonmetals generally is covalent. 

What factors determine whether an elemental substance adopts a metallic or a covalent structure From the simple model for metallic bonding, which views a metal as a lattice of cations embedded in a sea of delocalised electrons, it may be supposed that atoms having low ionisation potentials are most likely to become assembled as metallic substances. This correlation is far from perfect, however. Thus the first and second ionisation energies of mercury are comparable with those of sulphur, but the alchemists viewed elemental mercury and sulphur as the quintessential metal and nonmetal respectively. A closely-related correlation can be found with electronegativity. 

Vacancies Vacancies (empty atom sites) are indicated by the symbols Vm and Vx for metal, M, and nonmetal, X, sites respectively. Where confusion may occur with the atom vanadium, the symbol for a vacancy is written Va. Vacancies are created by the removal of neutral atoms from the crystal. This rule also applies to ionic solids. For example, in ionic NiO, Vxi would imply the removal of a Ni + cation together with two electrons, that is, a neutral Ni atom. Similarly, Vo... 

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