Chapter 15 Ionic Bonding and Ionic Compounds Walla Walla High School Mr. Carlsen
Section 15.1 Electron Configuration in Ionic Bonding l OBJECTIVES: –Use the periodic table to infer the number of valence electrons in an atom, and draw it’s electron dot structure. –Describe the formation of cations from metals, and of anions from nonmetals.
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
Section 15.2 Ionic Bonds l OBJECTIVES: –List the characteristics of an ionic bond. –Use the characteristics of ionic compounds to explain the electrical conductivity of ionic compounds when melted and when in aqueous solution.
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 = 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
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 l OBJECTIVES: –Use the theory of metallic bonds to explain the physical properties of metals. –Describe the arrangements of atoms in some common metallic crystal structures.
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. 15.13, 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. 15.14, p.427
Crystalline structure of metal l If made of one kind of atom, metals are among the simplest crystals l Note Fig. 15.16, p.428 for types: 1. Body-centered cubic: –every atom has 8 neighbors –Na, K, Fe, Cr, W
Crystalline structure of metal 2. Face-centered cubic: –every atom has 12 neighbors –Cu, Ag, Au, Al, Pb 3. Hexagonal close-packed –every atom also has 12 neighbors –different pattern due to hexagonal –Mg, Zn, Cd
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
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 Table 15.3, p.429 - common alloys l Types? a) substitutional alloy- the atoms in the components are about the same size l b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger l Amalgam- dental use, contains Hg