Video 2-4. Transfer of one electron from the Na atom to the F atom, followed by the formation of an ionic bond between the resultant Na+ cation and F- anion (source).
Note that the electron transferred from the Na to the F is denoted in Figure 2-42 as e-
, a common symbol for an electron in science. Now that we started talking about transfer of electrons in chemical reactions, we will be using this symbol (e-
We conclude that an ionic bond
is a chemical bond resulting from the mutual electrostatic attraction of oppositely charged ions. Substances featuring this type of bond, called ionic compounds
, are ubiquitous in chemistry and are all around us. For example, most salts, including sodium fluoride (NaF) considered above (Figure 2-42) and table salt (sodium chloride, NaCl) are typical ionic compounds. 2.4.4. Metals, Nonmetals, and Metalloids.
In Volume 1, we defined metals, nonmetals, and metalloids as simple substances on the basis of their physical properties and visual appearance. It is now time to define metals, nonmetals, and metalloids not only as simple substances, but also as chemical elements
(types of atoms). Metals as simple substances
are excellent conductors of electricity and heat, lustrous, ductile, and malleable. A metal as an element
is the type of atom that readily forms positively charged ions by willingly giving away its valence electron(s) to attain the stable n
(octet) electron configuration. A metal atom usually has one, two, or sometimes three (at the most) electrons in its valence shell. Nonmetals as simple substances
may be defined as those that lack "such characteristic properties of metals as hardness, mechanical adaptability, or the ability to conduct electricity.
" (While in general this is a reasonable definition, we should keep in mind that the alkali metals can be easily cut with a knife, that diamond is harder than any metal, that plastic sulfur
is very mechanically adaptable, and that graphite is an excellent conductor of electricity. However, diamond and graphite are allotropes of carbon and plastic sulfur is an allotropic form of sulfur. Both carbon and sulfur are undoubtedly nonmetals.) A nonmetal as an element
is the type of atom that is not prone to form cations by giving away its electrons. Atoms of nonmetallic elements have more than three valence electrons. Metalloids as simple substances
often exhibit some features of typical metals such as luster, while ultimately lacking in most characteristic properties of metals, such as high electrical conductivity. There are only a handful of commonly recognized metalloids: boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). A metalloid as a chemical element
. "There is no standard definition of a metalloid and no complete agreement on which elements are metalloids.
" In our course, we will categorize metalloid elements as nonmetals because, like nonmetals and unlike metals, metalloids have three or more electrons in their valence shells and are not inclined to form cations by losing their electrons. 2.4.5. Metallic Bond: What Metal Atoms Do When There Is No Electron Acceptor Around.
We know that a metal atom is prone to get rid of its outermost shell electron(s) to become a cation with the stable octet configuration. Where do these electrons go after they leave the metal atoms?
Electrons cannot disappear into nowhere. If there are some nonmetal atoms around, they are happy to accept the electrons from the metal to become anions; it is a win-win situation. But, what happens if there are no species that can accommodate the "extra" electrons that a metal atom wants to discard?
In their "pursuit of happiness", metal atoms have to take care of themselves, and they do. Metals in bulk exist as a lattice of cations immersed in the so-called electron gas
that acts as a "glue" to hold the metal ions together. The electron gas is the totality of electrons that have been discarded by the metal atoms and are now evenly spread throughout the entire body of the metallic substance. Figure 2-43 illustrates this metallic bonding
model using potassium (K) and calcium (Ca) as two examples.