Chapter 5

Ionic Bonding

Ions

Valence electrons: the electrons in the highest occupied energy level

Valence electrons can be determined by their electron configurations

Valence electrons largely determine the chemical properties of an element

Ions

The number of valence electrons is also related to the group number in the Periodic Table. All Alkali metals are in group 1 and have 1

valence electron.

Valence electrons are usually the only electrons used in the formation of chemical bonds

Ions

Electron dot structures: Shows valence electrons as dots. The inner electrons are represented by the elements symbol.

Ions

Octet rule: Atoms in compounds tend to have the electron configuration of a noble gas Typically 8 electrons in Highest nrg level Except He which has 2 electrons

Cations: are atoms that lose all valence electrons to gain the electron configuration of the nearest noble gas. (typically metals)

Ions

Ionization: process of becoming an ion

Alkali metals always form +1 ions

Alkaline Earth metals always form +2 ion

Ions

Anions: are atoms that gain electrons to achieve the electron configuration of the next noble gas. (Typically non-metals)

Halogens always form -1 ions

Ionic Bonds and Ionic Compounds

Ionic compounds: are formed when ions are bonded together and become electrically neutral. (Typically metal + nonmetal) a.k.a. salt

Ionic bonds: force of attraction that binds oppositely charged ions together. Cations (+) and Anions (-), opposite charges attract.

Ionic Bonds and Ionic Compounds

Chemical Formula – shows the kinds and numbers of atoms in the smallest representative unit of a substance

Formula Unit – lowest whole-number ratio of the ions in an ionic compound

Properties of Ionic Compounds

How do they occur? When these two atoms get near each other:

• The atom with low electronegativity gives electrons to the atom with high electronegativity until both have the same number of valence electrons as the nearest noble gas.

Cont’d

Once a cation and anion are formed, they stick to each other magnetically via electrostatic attraction. Once they’ve stuck together, the resulting material is called an ionic compound.

How to tell if a compound is ionic or not by looking at its formula:

1)When metals bond to nonmetals, they form ionic compounds.

2) The farther two elements are from one another on the periodic table, the more likely the compound is to be ionic.

3)If the electronegativity difference between the two elements is greater than about 1.7, the compound is said to be ionic. Chart of electronegativities is in your book on

p. 198. LiF is ionic because the electronegativity of Li

is 1.0 and F is 4.0 (3.0 difference).

Ionic Bonds and Ionic Compounds

Solid at room temperature / brittle cations and anions are locked tightly in place

because of opposite charges

Crystals: orderly repeating 3-D pattern

High melting point (> 4000C)

Conduct electricity when molten or in an aqueous solution (ions need to be moving to conduct electricity and in crystalline form they are too tightly packed)

Bonding in Metals

Metallic Bonds: attraction of free-flowing valence electrons to the (+) charged metallic ions.

The valence electrons of metal atoms can be modeled as a sea of electrons

Metals are arranged in very compact and orderly patterns

Bonding in Metals

Alloys – mixtures composed of two or more elements…at least one of which is a metal Brass is an alloy of copper and zinc

Alloys are important because their properties are often superior to those of their component elements