Chapter 15 Notes Ionic Bonding

Atoms to Ions Why do atoms become ions? To make them more stable… Octet rule: atoms tend to be more stable when they have a full valence shell of electrons

Electron Configuration of Ions We also have to look at what is going on inside of ions: Lets look at Na vs. Na + F vs. F -

Isoelectronic Note that F -, Na + and Ne are isoelectronic. They have the exact same number of electrons in the same configuration.

What is the electron configuration for: Ca 2+ N 3- Al 3+

Lewis Dot Structures To understand what occurs in an ionic bond, we must first look at the Lewis dot structure for atoms. Put the number of valence electrons around the symbol for the atom in the following order: X

What is the Lewis structure for: Cs Al Ne O I Sr

What is an ionic bond? Bond between a cation and an anion formed because of the electrostatic attraction of opposite charges. In other words, one atom gives away electrons, becoming positive. Another takes electrons, becoming negative. These two opposite charges will attract forming an ionic bond.

Electrons in Ionic Bonds Using the electron dot structure, we can show what happens in an ionic compound. For example, between magnesium and iodine…

Show the ionic bonding diagram between: Sodium and chlorine Lithium and oxygen Aluminum and sulfur

Properties of Ionic Compounds At room temperature, ionic compounds are crystalline solids. The ions arrange themselves in a three-dimensional pattern that gives rise to a distinctive crystalline shape.

Properties, cont. Ionic compounds tend to be fairly brittle, due to the rigid bonding patterns in the crystalline structure Also, ionic compounds can conduct electricity when in a molten or aqueous state.

Metallic Bonding Metals also bond together, but not in the same way as ionic compounds. Metals exist as tightly packed cations surrounded by a “sea of electrons”, much like a community pool of the valence electrons.

Properties of metals This explains several properties of metals. For example, metals are good conductors because the electrons can flow freely between atoms in the metal. Also, malleability/ductility can be explained by the fact that (unlike in ionic crystals) the cations are insulated from each other by the electrons, and can freely slide past one another, rather than fracturing off when struck.

Arrangement of atoms In a metal, the atoms can be arranged in several configurations. Three examples are: –Body centered cubic –Face centered cubic –Hexagonal close-packed