Ionic Bonds

What are ionic bonds?

Bonds which occur between two atoms with highly different electronegativities such that one atom ``pulls'' the electron(s) of the other atom towards itself; these bonds commonly involve a metal and a non-metal atom. The difference in charge of the two atoms is the electrostatic force that holds the atoms together. Sodium chloride, NaCl, is a good example of this in Figure 30.1 below:

Figure 30.1: The Ionic Bond: In ionic bonds such as NaCl, the difference in charge of the two atoms is the electrostatic force that maintains the bond between the atoms. Note that when NaCl is in an aqueous environment, the electron transfer creates two ions: a cation (Na$^{+}$) and an anion (Cl$^{-}$).

What is the Octet Rule?

The desire for atoms to share, lose or gain electrons to have the same number of electrons of the nearest noble gas.

All noble gases have eight valence electrons except He, why?

Well, He only has an s orbital and therefore has only two valence electrons. The other noble gases also have a p orbital which are full with six electrons. The six $p$ orbital electrons - plus the two s orbital electrons - equal eight.

What are the exceptions to the octet rule?

As for many rules, the octet rule has exceptions. For example boron, phosphorus, sulfur and xenon. For studying purposes know that they exist. To be sure on the test, calculate formal charges to make sure that you have the right number of electrons (see Formal Charges below on page ).

What is lattice energy?

The energy released when gaseous ions of opposite charge come together to form a solid.

How is lattice energy calculated?

$$E_{Lattice} = \frac{kQ_{1}Q_{2}}{r_{2}}$$ (31.1)

Where $k$ is a constant, $Q_{1}$ and $Q_{2}$ are the charges on the particles, and $r_{2}$ is the distance between their centers squared, aka Coulumb's Law.

Note: this discussion on lattice energy may bring to mind bond dissociation energies, etc. These will be discussed in Chapter 38 Thermochemistry on page and Coulomb's Law will be discussed in Chapter 67 Physics on page .