3Valence Electrons are…? Valence electrons – The s and p electrons in the outer energy levelthe highest occupied energy levelCore electrons – electrons in the energy levels below.The electrons responsible for the chemical properties of atoms, and are those in the outer energy level.
4Keeping Track of Electrons Atoms in the same column...Have the same outer electron configuration.Have the same valence electrons.Electron configuration of Group 1A?𝒔 𝟏Number of valence electrons in Group 1A?1
5The number of valence electrons are easily determined The number of valence electrons are easily determined. It is the group number for a representative elementGroup 2A: Be, Mg, Ca, etc.have 2 valence electrons
6Electron Dot diagrams are… A way of showing valence electrons.How to write them?Write the symbol – represents the nucleus and inner (core) electronsPut one dot for each valence electron (8 maximum)They don’t pair up until they have to (Hund’s rule)X
7The Electron Dot diagram for Nitrogen Nitrogen has 5 valence electrons to show.First we write the symbol.NThen add 1 electron at a time to each side.Now they are forced to pair up.We have now written the electron dot diagram for Nitrogen.
9The Octet RuleThe Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer levelEach noble gas (except He, which has 2) has 8 electrons in the outer levelIn Chapter 6, we learned that noble gases are unreactive in chemical reactionsIn 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules
10Formation of CationsMetals lose electrons to attain a noble gas configuration.Where are metals located? LeftMake positive ions (cations)
11Formation of CationsIf we look at the electron configuration, it makes sense to lose electrons:Na 1s22s22p63s1 1 valence electronNa1+ 1s22s22p6 This is a noble gas configuration with 8 electrons in the outer level.
12Electron Dots For Cations Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electronsCa
13Electron Dots For Cations Metals will lose all valence electronsCa
14Electron Dots For Cations Metals will lose the valence electronsForm positive ionsCa2+This is the “calcium ion”.NO DOTS are now shown for the cation.
15Practice Cation formed Na = 1 𝑁𝑎 +1 Mg = 2 𝑀𝑔 +2 Al = 3 𝐴𝑙 +3 # of valence electronNa = 1Mg = 2Al = 3Cation formed𝑁𝑎 +1𝑀𝑔 +2𝐴𝑙 +3
17Electron Dots For Cations Let’s do Scandium, #21The electron configuration is: 1s22s22p63s23p64s23d1Thus, it can lose 2e- (making it 2+), or lose 3e- (making 3+)Sc = Sc2+Sc= Sc3+Scandium (II) ionScandium (III) ion
18Electron Dots For Cations Let’s do Silver, element #47Predicted configuration is: 1s22s22p63s23p64s23d104p65s24d9Actual configuration is: 1s22s22p63s23p64s23d104p65s14d10Ag = Ag1+ (can’t lose any more, charges of 3+ or greater are uncommon)
19Electron Dots For Cations Silver did the best job it could, but it did not achieve a true Noble Gas configurationInstead, it is called a “pseudo-noble gas configuration”
20Electron Configurations: Anions Nonmetals gain electrons to attain noble gas configuration.They make negative ions (anions)S = 1s22s22p63s23p4 = 6 valence electronsS2- = 1s22s22p63s23p6 = noble gas configuration.Halide ions - ions from chlorine or other halogens that gain electrons
21Electron Dots For Anions Nonmetals will have many valence electrons (usually 5 or more)They will gain electrons to fill outer shell.3-P(This is called the “phosphide ion”, and shows dots)
22Stable Electron Configurations All atoms react to try and achieve a noble gas configuration.Noble gases have 2 s and 6 p electrons.8 valence electrons = stableThis is the octet rule (8 in the outer level is particularly stable).Ar
23Review How many valence electrons do the following elements have? Ga = 3K = 1P = 5Li = 1Cl = 7He = 2S = 6F = 7Mg = 2Ne = 8
24Review Draw the electron dot structure of the following elements. GaKPHeSFMgNe
25Review What ions will the following elements form? 𝐺𝑎 +3𝑀𝑔 +2𝑃 −3𝐹 −1𝐾 +1𝑆 −2
43Ionic Bonding= Ca3P2Chemical formula- shows the kinds and numbers of atoms in the smallest representative particle of the substance.
44Balancing Ionic formulas Crisscross methodThe numerical value of the charge of each ion is crossed over and becomes the subscript for the other ion.
45Practice What will the chemical formula look like? ElementsCa+2 F-Al+3 O-2Ca+2 O-2Formula𝐶𝑎𝐹 2𝐴𝑙 2 𝑂 3𝐶𝑎𝑂
46Properties of Ionic Compounds Crystalline solids – regular repeating arrangement of ionsStrongly bonded together.Structure is rigid.High melting pointsCoordination number- number of ions of opposite charge surrounding it
47NaCl CsCl TiO2 - Page 198 Coordination Numbers: Both the sodium and chlorine have 6NaClBoth the cesium and chlorine have 8CsClEach titanium has 6, and each oxygen has 3TiO2
48Do they Conduct?Conducting electricity means allowing charges to move.In a solid, the ions are locked in place.Ionic solids are insulators.When melted, the ions can move.Melted ionic compounds conduct.NaCl: must get to about 800 ºC.Dissolved in water, they also conduct (free to move in aqueous solutions)
49- Page 198The ions are free to move when they are molten (or in aqueous solution), and thus they are able to conduct the electric current.
50Review What is the formula unit for the following compounds? KCl 1:1𝐹𝑒 2 𝑂 :3𝐹𝑒𝑆 2 1:2𝐵𝑎𝑆𝑂 :1:4HgS 1:1𝑁𝑎 2 𝑂 2:1
51Practice What will the chemical formula look like? ElementsNa+ Cl-Mg+2 F-Ca+2 N-3Al+3 N-3K+ S-2Formula𝑁𝑎𝐶𝑙𝑀𝑔𝐹 2𝐶𝑎 3 𝑁 2𝐴𝑙𝑁𝐾 2 𝑆
53Metallic Bonds are… How do we get sheets of Aluminum (or any metal)? Metals hold on to their valence electrons very weakly.Think of them as positive ions (cations) floating in a sea of electrons
54Sea of Electrons + Electrons are free to move through the solid. Metals conduct electricity.+
55Metals are Malleable Hammered into shape (bend). Ductile - drawn into wires.Both malleability and ductility explained in terms of the mobility of the valence electrons
56Due to the mobility of the valence electrons, metals have: - Page 201Due to the mobility of the valence electrons, metals have:Notice that the ionic crystal breaks due to ion repulsion!1) Ductility2) Malleabilityand
60Ionic solids are brittle Strong Repulsion breaks a crystal apart, due to similar ions being next to each other.+-Force+-+-+-
61Crystalline structure of metal Metals are arranged in very compact and orderly patterns.
62Alloys Alloys - mixtures of 2 or more elements, at least 1 is a metal Made by melting a mixture of elements, then coolingBrass: an alloy of Cu and ZnBronze: Cu and Sn
63Why use alloys? Properties are often superior to the pure element Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tablewareSteels are very important alloyscorrosion resistant, ductility, hardness, toughness, cost
65Predicting Ionic Charges Group B elements:Many transition elementshave more than one possible oxidation state.Note the use of Roman numerals to show chargesIron (II) = Fe2+Iron (III) = Fe3+
66Naming cationsTwo methods can clarify when more than one charge is possible:Stock system – uses roman numerals in parenthesis to indicate the numerical valueClassical method – uses root word with suffixes (-ous, -ic)Does not give true value
67Naming cations We will use the Stock system. Cation - if the charge is always the same (like in the Group A metals) just write the name of the metal.Transition metals can have more than one type of charge.Indicate their charge as a roman numeral in parenthesis after the name of the metal (Table 9.2, p.255)
68Predicting Ionic Charges Some of the post-transition elements alsohave more than one possible oxidation state.Tin (II) = Sn2+Lead (II) = Pb2+Tin (IV) = Sn4+Lead (IV) = Pb 4+
69Predicting Ionic Charges Group B elements:Some transition elementshave only one possible oxidation state, such as these three:Silver = Ag1+Zinc = Zn2+Cadmium = Cd2+
70Do not need to use roman numerals for these: Exceptions:Some of the transition metals have only one ionic charge:Do not need to use roman numerals for these:Silver is always 1+ (Ag1+)Cadmium and Zinc are always 2+ (Cd2+ and Zn2+)
71Practice by naming these: Ca2+Al3+Fe3+Fe2+Pb2+Li1+
72Write symbols for these: Potassium ionMagnesium ionCopper (II) ionChromium (VI) ionBarium ionMercury (II) ion
73Anions are always the same charge Naming AnionsAnions are always the same chargeChange the monatomic element ending to – ideF1- a Fluorine atom will become a Fluoride ion.
75Write symbols for these: Sulfide ionIodide ionPhosphide ionStrontium ion
76Polyatomic ions are…Groups of atoms that stay together and have an overall charge, and one name.Usually end in –ate or -iteAcetate: C2H3O21-Nitrate: NO31-Nitrite: NO21-Permanganate: MnO41-Hydroxide: OH1- and Cyanide: CN1-?
77(One of the few positive polyatomic ions) Know Table 9.3 on page 257Phosphate: PO43-Phosphite: PO33-Ammonium: NH41+Sulfate: SO42-Sulfite: SO32-Carbonate: CO32-Chromate: CrO42-Dichromate: Cr2O72-(One of the few positive polyatomic ions)If the polyatomic ion begins with H, then combine the word hydrogen with the other polyatomic ion present: H CO → HCO hydrogen + carbonate → hydrogen carbonate ion
78Writing Ionic Compound Formulas Example: Barium nitrate (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!( )Ba2+NO3-22. Check to see if charges are balanced.Now balanced.Not balanced!= Ba(NO3)23. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance subscripts.
79Writing Ionic Compound Formulas Example: Ammonium sulfate (note the 2 word name)( )1. Write the formulas for the cation and anion, including CHARGES!NH4+SO42-2Now balanced.2. Check to see if charges are balanced.Not balanced!= (NH4)2SO43. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
80Writing Ionic Compound Formulas Example: Iron (III) chloride (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!Fe3+Cl-3Now balanced.2. Check to see if charges are balanced.Not balanced!= FeCl33. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
81Writing Ionic Compound Formulas Example: Aluminum sulfide (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!Al3+S2-232. Check to see if charges are balanced.Now balanced.Not balanced!= Al2S33. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
82Writing Ionic Compound Formulas Example: Magnesium carbonate (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!Mg2+CO32-2. Check to see if charges are balanced.They are balanced!= MgCO3
83Writing Ionic Compound Formulas Example: Zinc hydroxide (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!( )Zn2+OH-2Now balanced.2. Check to see if charges are balanced.Not balanced!= Zn(OH)23. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion. Use the criss-cross method to balance the subscripts.
84Writing Ionic Compound Formulas Example: Aluminum phosphate (note the 2 word name)1. Write the formulas for the cation and anion, including CHARGES!Al3+PO43-2. Check to see if charges are balanced.They ARE balanced!= AlPO4
85Naming Ionic Compounds 1. Name the cation first, then anion2. Monatomic cation = name of the elementCa2+ = calcium ion3. Monatomic anion = root + -ideCl- = chlorideCaCl2 = calcium chloride
86Naming Ionic Compounds (Metals with multiple oxidation states)some metals can form more than one charge (usually the transition metals)use a Roman numeral in their name:PbCl2 – use the anion to find the charge on the cation (chloride is always 1-)Pb2+ is the lead (II) cationPbCl2 = lead (II) chloride
87Things to look for:If cations have ( ), the number in parenthesis is their charge.If anions end in -ide they are probably off the periodic table (Monoatomic)If anion ends in -ate or –ite, then it is polyatomic
88Practice by writing the formula or name as required… Iron (II) PhosphateStannous FluoridePotassium SulfideAmmonium ChromateMgSO4FeCl3