Chapter 9 - Models of Chemical Bonding

The kind and strength of chemical bonds govern the characteristics of a material, much as the electron configuration and the strength of nucleus-electron interactions affect the properties of an atom.

Bonding, in general, reduces the potential energy difference between positive and negative particles, whether they be oppositely charged ions or nuclei and electrons. Metal with nonmetal: electron transport and ionic bonding, as seen in the picture below.

A metal atom (low IE) loses its one or two valence electrons, and a nonmetal atom (highly negative EA) gains the electron(s). As the transfer of electron(s) from the metal atom to the nonmetal atom occurs, each atom forms an ion with a noble gas electron configuration.

The electrostatic attractions between these positive and negative ions draw them into a three-dimensional array to form an ionic solid. The chemical formula of an ionic compound is the empirical formula because it gives the cation-to-anion ratio.

Electron sharing and covalent bonding between nonmetals, as shown in the image above.

When two atoms have little or no difference in their proclivity to lose or gain electrons, we have electron sharing and covalent bonding, which is most frequent between nonmetals:

• Each nonmetal atom strongly retains its own electrons (high IE) and attracts other electrons as well (highly negative EA).

• Each atom in the bond's nucleus pulls the valence electrons of the other, drawing the atoms together.

The shared electron pair is generally concentrated between the two atoms, forming a covalent connection of a certain length and strength between them.

When atoms connect covalently, they usually form distinct molecules.

It is important to note that the chemical formula of a covalent substance is the molecular formula since it specifies the number of atoms in each molecule.

Electron pooling and metallic bonding between metals, as shown in the image attached above. Metals share electrons via metallic bonding rather than covalent bonding:

• Their atoms are big, and the few outside electrons are well protected by filled interior levels (core electrons). As a result, metals shed outer electrons quickly (low IE) but do not easily acquire them (slightly negative or positive EA).

• The massive number of atoms in a metal sample pool their valence electrons in a "sea" of electrons that "flows" between and around each metal-ion core (nucleus + inner electrons), attracting and keeping them together.

Unlike in covalent bonding, electrons are not localized.

Almost all naturally occurring compounds are made up of atoms or ions that are linked to one another. Atoms can reduce their energy by chemical bonding.

When metal atoms donate electrons to nonmetal atoms, the resulting ions attract one other and create an ionic solid. Covalent bonding is more frequent between nonmetal atoms and produces distinct molecules.

Bonded atoms share one or more electron pairs that are confined between them. Metallic bonding occurs when a large number of metal atoms pool their valence electrons into a delocalized electron "sea" that keeps all the atoms in the sample together.

Points of melting and boiling. Almost all metals are solids with moderate to high melting and boiling points (Table 9.5). These qualities are connected to the metallic bonding's energy.

Because the cations can migrate without disturbing their attraction to the surrounding electrons, melting temperatures are only moderately high.

Because each cation and its valence electron(s) must separate from the others in order to evaporate, boiling points are quite high. Gallium is a good example: it can melt in your fingers (mp 29.8°C) but doesn't boil until it reaches above 2400°C.

The valence electrons of the metal atoms in a sample, according to the electron-sea concept, are highly delocalized and attract all of the metal cations, keeping them together.

Metals have only moderately high melting points because metal ions remain attracted to the electrons in the electron sea, even if their relative positions change.

Metals have very high boiling points because vaporization involves the complete separation of individual cations with their valence electrons from all the others.