Chapter 8 Ionic Bonding

Keeping Track of Electrons l The electrons responsible for the chemical properties of atoms are those in the outer energy level. l Valence electrons - The s and p electrons in the outer energy level. l Core electrons -those in the energy levels below.

Keeping Track of Electrons l Atoms in the same column l Have the same outer electron configuration. l Have the same valence electrons. l Easily found by looking up the group number on the periodic table. l Group 2A - Be, Mg, Ca, etc.- l 2 valence electrons

Electron Dot diagrams l A way of keeping track of valence electrons. l How to write them l Write the symbol. l Put one dot for each valence electron l Don’t pair up until they have to X G. N. Lewis

The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons. l First we write the symbol. N l Then add 1 electron at a time to each side. l Until they are forced to pair up.

Write the electron dot diagram for l Na l Mg lClC lOlO lFlF l Ne l He

Electron Configurations for Cations l Metals lose electrons to attain noble gas configuration. l They make positive ions. l If we look at electron configuration it makes sense. l Na 1s 2 2s 2 2p 6 3s valence electron l Na + 1s 2 2s 2 2p 6 -noble gas configuration

Electron Dots For Cations l Metals will have few valence electrons Ca

Electron Dots For Cations l Metals will have few valence electrons l These will come off Ca

Electron Dots For Cations l Metals will have few valence electrons l These will come off l Forming positive ions Ca +2

Electron Configurations for Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions. l If we look at electron configuration it makes sense. l S 1s 2 2s 2 2p 6 3s 2 3p valence electrons l S -2 1s 2 2s 2 2p 6 3s 2 3p 6 -noble gas configuration.

Electron Dots For Anions l Nonmetals will have many valence electrons. l They will gain electrons to fill outer shell. P P -3

Stable Electron Configurations l All atoms react to achieve noble gas configuration. l Noble gases have 2 s and 6 p electrons. l 8 valence electrons. l Also called the octet rule. Ar

Ionic Bonding l Anions and cations are held together by opposite charges. MovieMovie l Ionic compounds (metal plus nonmetal) are called salts. l Covalent bonds are between nonmetals. l Simplest ratio in ionic bonds is called the formula unit. l The bond is formed through the transfer of electrons. l Electrons are transferred to achieve noble gas configuration. MovieMovie

Ionic Bonding NaCl

Ionic Bonding Na + Cl -

Ionic Bonding l All the electrons must be accounted for! CaP

Ionic Bonding CaP

Ionic Bonding Ca +2 P

Ionic Bonding Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca

Ionic Bonding Ca +2 P -3 Ca P

Ionic Bonding Ca +2 P -3 Ca +2 P

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P -3 Ca +2

Ionic Bonding Ca 3 P 2 Formula Unit MovieMovie

Properties of Ionic Compounds l Crystalline structure. l A regular repeating arrangement of ions in the solid. l Ions are strongly bonded. l Structure is rigid. l High melting points- because of strong forces between ions.

Crystalline Structure

Do they Conduct? l Conducting electricity is allowing charges to move. l In a solid, the ions are locked in place. l Ionic solids are insulators. l When melted, the ions can move around. l Melted ionic compounds conduct. l First get them to 800ºC. l Dissolved in water they conduct.

Metallic Bonds l How atoms are held together in 3-D solid or a crystal lattice. l Metals hold onto their valence electrons very weakly. l Think of them as positive ions floating in a sea of electrons. Electrons are considered “delocalized”

Sea of Electrons l Electrons are free to move through the solid. l Metals conduct electricity.

Metals are Malleable and Ductile l Malleable - Hammered into shape (compression force). l Ductile - drawn into wires (tension force).

Malleable (compression)

l Electrons allow atoms to slide by.

Ionic solids are brittle

l Strong Repulsion breaks crystal apart.

Alloys l We use lots of metals every day, but few are pure metals l Alloys - mixtures of 2 or more elements, at least 1 is a metal l made by melting a mixture of the ingredients, then cooling l Brass: an alloy of Cu and Zn l Bronze: Cu and Sn MovieMovie

Why use alloys? l Properties often superior to element l Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware l Steels are very important alloys –corrosion resistant, ductility, hardness, toughness, cost