Thursday, Jan. 16 th : “A” Day Friday, Jan. 17 th : “B” Day Agenda  Go over Sec. 5.1 Quiz  Finish Section 5.2: “Ionic Bonding and Salts” Properties of ionic compounds, crystal lattice, unit cell  In-Class: Sec. 5.2 review, Pg. 175: #1-10  Homework: “Positive and Negative Ions” worksheet Concept Review: “Ionic Bonding and Salts”

5.1 Quiz: “Simple Ions”  This quiz seemed to give a lot of students trouble so I wanted to take some time and go over it… 1.Which of the following electron configurations belong to an element that is the most chemically reactive? a.1s 2 b.1s 2 2s 2 2p 6 c.1s 2 2s 2 2p 5 d.1s 2 2s 2 2p 6 3s 2 3p 6

5.1 Quiz: “Simple Ions” 2.An octet is equal to: a.2 b.4 c.5 d.8

5.1 Quiz: “Simple Ions” 3.How many valence electrons does the element with the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 have? a.0 b.1 c.9 d.19

5.1 Quiz: “Simple Ions” 4.Which of the following situations will cause the element with the electron configuration 1s 2 2s 2 2p 5 to have an octet configuration? a.Loss of one electron b.Gain of one electron c.Loss of two electrons d.Gain of three electrons

5.1 Quiz: “Simple Ions” 5.Which of the following situations will cause the element with the electron configuration 1s 2 2s 2 2p 6 3s 2 to have an octet configuration? a.Loss of one electron b.Gain of one electron c.Loss of two electrons d.Gain of three electrons

5.1 Quiz: “Simple Ions” 6.The elements of Group _____ are able to satisfy the octet rule without forming compounds. a.1 b.2 c.17 d.18

5.1 Quiz: “Simple Ions” 7.Stable ions of which of the following elements do NOT have octets of valence electrons? a.F b.Na c.Cl d.Fe

5.1 Quiz: “Simple Ions” 8.An element with the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 will ionize to a(n) a.Anion b.Cation c.Noble gas d.Both (a) and (b)

5.1 Quiz: “Simple Ions” 9.An element with the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 5 will ionize to a(n) a.Anion b.Cation c.Noble gas d.Both (a) and (b)

5.1 Quiz: “Simple Ions” 10. An ion and its parent atom differ in a.Electron configuration b.Number of electrons c.Chemical reactivity d.All of the above

Ionic Compounds  Remember, salts are electrically neutral ionic compounds made of cations and anions.  The ratio of cations to anions is always such that an ionic compound has no overall charge.  =  Examples: Na + + Cl - NaCl Mg 2+ + O 2- MgO

5 Properties of Ionic Compounds 1.Ionic compounds do not consist of molecules. 2.Ionic bonds are strong. 3.Ionic compounds have distinctive properties. 4.Liquid and dissolved salts conduct electric current. 5.Salts are hard and brittle.

1. Ionic Compounds Do Not Consist of Molecules  Water is a molecular compound, so individual water molecules are each made of two hydrogen atoms and one oxygen atom. (no ions involved)  Sodium chloride is an ionic compound, so it is made up of many Na + and Cl  ions all bonded together to form a crystal. There are no NaCl molecules, just Na + and Cl - ions.

1. Ionic Compounds Do Not Consist of Molecules cont…  Metals and non-metals tend to form ionic compounds and not molecular compounds.  The formula MgO likely indicates an ionic compound because Mg is a metal and O is a non- metal.  In contrast, the formula CO likely indicates a molecular compound because both C and O are non-metals.  Lab tests are needed to confirm such indications.

2 Simple Rules to Tell if a Compound is Ionic or Covalent  Ionic Compounds: metal element + non-metal element = ionic  Covalent Compounds: non-metal element + non-metal element = covalent

2. Ionic Bonds Are Strong  Attractive forces exist between oppositely charged ions and involve more than a single cation and anion.  Six Na + ions surround each Cl  ion and vice versa.  As a result, the attractive force between oppositely charged ions is significantly greater in a crystal than it would be if the ions existed only in pairs.  Overall, the attractive forces are much stronger than the repulsive ones, so ionic bonds are strong.

3. Ionic Compounds Have Distinctive Properties  Most ionic compounds have high melting and boiling points because of the strong attraction between ions.  To melt, ions cannot be in fixed locations.  Because the bonds between ions are strong, a lot of energy is needed to free them.  Still more energy is needed to move ions out of the liquid state and cause boiling, so ionic compounds are rarely gases at room temperature.

Melting/Boiling Points of Ionic/Covalent Compounds

4. Liquid and Dissolved Salts Conduct Electric Current  To conduct an electric current, a substance must satisfy two conditions: it must contain charged particles those particles must be free to move  Ionic solids, such as salts, generally are not conductors because the ions can’t move.  When a salt melts or dissolves in water, the ions can move around so they are excellent electrical conductors.

Sodium Chloride in 3 Phases

5. Salts are Hard and Brittle  Like NaCl, most ionic compounds are hard and brittle. Hard means that the crystal is able to resist a large force applied to it. Brittle means that when the applied force becomes too strong to resist, the crystal develops a widespread fracture rather than a small dent.  Both properties are due to the patterns in which the cations and anions are arranged in all salt crystals.

5. Salts are Hard and Brittle cont…  The ions in a crystal are arranged in a repeating pattern, forming layers.  If a force causes one layer to move, ions of the same charge will be positioned next to each other.  This is why all salts shatter along a line extending through the crystal known as a cleavage plane.

*How to Identify a Compound as Ionic* 1.All ionic compounds are solids at room temp. 2.Tap it gently: Ionic compounds are hard/brittle and should not break apart easily. If it does break, it should fracture into crystals and not into a powder. 3.Heat it: Ionic compounds have high melting and boiling points. 4.Test conductivity: Ionic compounds are good conductors in liquid form. 5.Dissolve in water: Ionic compounds conduct electric current when dissolved in water.

Salt Crystals  Despite their differences, the crystals of all salts are made of simple repeating units.  These repeating units are arranged to form a crystal lattice, the regular pattern in which a crystal is arranged.  These repeating patterns within a salt are the reason for the crystal shape that can be seen in most salts

Crystal Structure Depends on the Sizes and Ratios of Ions  Formulas indicate ratios of ions. For example, the formula for NaCl indicates there is a 1:1 ratio of sodium cations to chloride anions.  Within a NaCl crystal, each Na + ion is surrounded by six Cl  ions, and each Cl  ion by six Na + ions.  Because the edges of the crystal do not have this arrangement, they are locations of weak points.

Crystal Structure Depends on the Sizes and Ratios of Ions  The arrangement of cations and anions to form a crystal lattice depends on the size of the ions and the ratio of cations to anions. For example, the salt calcium fluoride, CaF 2, has one Ca 2+ ion for every two F  ions.  The cations and anions in calcium fluoride also have a greater difference in size than those in NaCl.

Crystal Structure Depends on the Sizes and Ratios of Ions  Because of the size differences of its ions and their ratio in the salt, the crystal lattice structure of calcium fluoride (CaF 2 ) is different from that of sodium chloride (NaCl).  Each calcium ion is surrounded by eight fluoride ions.  At the same time, each fluoride ion is surrounded by four calcium ions.

Salts Have Ordered Packing Arrangements  All salts are made of repeating units.  The smallest repeating unit in a crystal lattice is called a unit cell.  Unit Cell: the smallest portion of a crystal lattice that shows the 3-dimensional pattern of the entire lattice.  The ways in which a salt’s unit cells are arranged are determined by X-ray diffraction crystallography.

In-Class Assignment/Homework  In-Class: Section 5.2 review, Pg. 175: #1-10  Homework: “Positive and Negative Ions” worksheet Concept Review: “Ionic Bonding and Salts”  You may work with a partner…  Quiz over Sec. 5.2 next time!