Chapter 15 Ionic Bonding and Ionic Compounds

Valence 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 –the highest occupied energy level l Core electrons -those in the energy levels below.

Keeping Track of Electrons l Atoms in the same column... –Have the same outer electron configuration. –Have the same valence electrons. l Easily found: group number on the periodic table for representative elem. l Group 2A: Be, Mg, Ca, etc. –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 (Hund’s rule) X

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 electron dot diagrams: l Na l Mg lClC lOlO lFlF l Ne lVlV

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

Electron Dots For Cations l Metals will have few valence electrons (usually 3 or less) 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+ Now make Sc an ion. Pseudo-noble gas configuration

Electron Configurations for Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions (anions) l Halide ions- ions from chlorine or other halogens that gain electrons l S 1s 2 2s 2 2p 6 3s 2 3p 4 6 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 (usually 5 or more) 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

Based on the electron dot diagrams from before write the charge for each element: l Na l Mg lClC lOlO lFlF l Ne lVlV

Section 15.2 Ionic Bonds

Ionic Bonding l Anions and cations are held together by opposite charges. l Ionic compounds are called salts. l Simplest ratio is called the formula unit. l The bond is formed through the transfer of electrons. l Electrons are transferred to achieve noble gas configuration.

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 Sample Problem 15-1, page 421

Properties of Ionic Compounds l Crystalline structure, usually solids l A regular repeating arrangement of ions in the solid: Fig. 15.9, p.423 l Ions are strongly bonded together. l Structure is rigid. l High melting points l Coordination number- number of ions of opposite charge surrounding it

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. –NaCl: must get to about 800 ºC. l Dissolved in water they conduct (aqueous)

Section 15.3 Bonding in Metals

Metallic Bonds l How atoms are held together in the solid. l Metals hold on to their valence electrons very weakly. l Think of them as positive ions (cations) floating in a sea of electrons: Fig , p.427

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

Metals are Malleable l Hammered into shape (bend). l Also ductile - drawn into wires. l Both malleability and ductility explained in terms of the mobility of the valence electrons l Fig , p.427

Malleable

l Electrons allow atoms to slide by.

Ionic solids are brittle

l Strong Repulsion breaks crystal apart.

Alloys 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

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

Why use alloys? l Types? – a) substitutional alloy- the atoms in the components are about the same size –b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger