Chemical Bonds Chapter 6

Compare – Eyes on Chemistry Epsom Salts Rock Salt Sucrose One more… WHAT DO YOU NOTICE ABOUT THEIR STRUCTURE?

Valence Electrons and Lewis Dot Structure (AKA Electron Dot) Remember: Octet Rule? Valence Electrons? How many valence electrons in… Example Sulfur (A#16) Your turn 1-20 – count off!

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Stable Electron Configurations

Ionic Bonding Relationships are weaker when you take/borrow/steal… It means someone had to give/lend/be robbed Where the analogy breaks down… Who is left feeling more negative? Who is more positive? What happens when negatives and positive are near each other?

Ca+ion vs. Anion

NaCl

Oxidation # - Can you predict which elements will form ionic bonds with which? - Which groups with which groups? - Metals with Metals? Metals with Non-metals?

MgCl2

Covalent Bonding (6.2) Relationships are stronger when you share Bond Strength -- Covalently bond > Ionic bonds One pair of shared electrons? Two pairs of shared electrons? Three pairs of shared electrons ? Three fish

Molecules = ? - Define it! Lewis Dot of Covalent Bonds – Molecule = neutral group of atoms held together by one or more covalent bonds Dr. B - Practice

Polar Covalent Bond Share…but not equally Results in partial charges = polarity EXAMPLE: Water

Nonpolar Covalent Bonds Name Formula Carbon dioxide (CO2) Carbon dioxide (CO2) has two polar C-O bonds, but the geometry of CO2 is linear so that the two bond dipole moments cancel and there is no net molecular dipole moment; the molecule is non-polar. In methane, the bonds are arranged symmetrically (in a tetrahedral arrangement) so there is no overall dipole. Formula: CH4 Shape Matters! Geometry Symmetry

Nonpolar Covalent Bonds Formula: CH4 Name: Methane Carbon dioxide (CO2) has two polar C-O bonds, but the geometry of CO2 is linear so that the two bond dipole moments cancel and there is no net molecular dipole moment; the molecule is non-polar. In methane, the bonds are arranged symmetrically (in a tetrahedral arrangement) so there is no overall dipole. Carbon dioxide (CO2) Shape Matters! Geometry Symmetry

Molecular Compound – bonded molecules Forces of attraction that hold molecules together in a liquid or solid - Stronger in polar or nonpolar molecules? Stronger in polar molecules… Ex. Hydrogen bonds (Van der Waals Forces)

Nomenclature -- How do you name or talk about compounds and molecules? Formulas - describes the ratio of ions in the compound Name – words to describe/identify it. Binary compound = only two elements Metal + Nonmetal = ? Nonmetal + Nonmetal = ? Metal + Metal = ? Metal + Nonmetal = ionic bonds => ionic compound Nonmetal + Nonmetal = covalent bonds => molecule Metal + Metal = metallic bonds

Talking Ionically… Pattern/Rules for Name… name of cation + name of anion + “-ide” When writing an ionic formula between a metal and a nonmetal follow these 5 steps: Write the symbols for the metal and the nonmetal. Write the valences as superscripts above each symbol. Drop the + and - sign. Crisscross the valences so they become the subscript for the other element. Reduce subscripts whenever possible. Only when both are divisible by a number greater than one.

Show me how…

Practice Using a periodic table try these then check your answers. sodium and phosphorus magnesium and fluorine aluminum and sulfur calcium and nitrogen barium and iodine potassium and bromine aluminum and phosphorus strontium and oxygen magnesium and nitrogen cesium and phosphorus Check your answers sodium and phosphorus = Na3P magnesium and fluorine = MgF2 aluminum and sulfur = Al2S3 calcium and nitrogen = Ca3N2 barium and iodine = BaI2 potassium and bromine = KBr aluminum and phosphorus = AlP strontium and oxygen = SrO magnesium and nitrogen = Mg3N2 cesium and phosphorus = Cs3P

When the metal (ca+ion) is a Transition Metal… More than one type of ions possible A Roman numeral in parentheses, following the name of the element, is used for elements that can form more than one positive ion. This is usually seen with metals. You can use a chart to see the possible valences for the elements. Fe2+ Iron (II) Fe3+ Iron (III) Use Roman Numerals to indicate the charge Ex. Copper (II) ion + Chlorine  Cu2+ + __Cl-  CuCl? Cu+ Copper (I) Cu2+ Copper (II) Cu2+ + _2_Cl-  CuCl2 Cu+ Cuprous Cu2+ Cupric -ous and -ic Although Roman numerals are used to denote the ionic charge of cations, it is still common to see and use the endings -ous or -ic. These endings are added to the Latin name of the element (e.g., stannous/stannic for tin) to represent the ions with lesser or greater charge, respectively. The Roman numeral naming convention has wider appeal because many ions have more than two valences. Fe2+ Ferrous Fe3+ Ferric

Ionic Compounds - Naming of anions -ide The -ide ending is added to the name of a monoatomic ion of an element. H- Hydride F- Fluoride O2- Oxide S2- Sulfide N3- Nitride P3- Phosphide -ite and -ate Some polyatomic anions contain oxygen. When an element forms two oxygen containing anions they are named with different suffixes/endings: -ite = the one with less oxygen -ate = the one with more oxygen Examples: NO2- Nitrite NO3- Nitrate SO32- Sulfite SO42- Sulfate

Practice Using a periodic table try these then check your answers. iron(III) and phosphorus copper(II) and fluorine silver(I) and sulfur manganese(II) and nitrogen lead(IV) and iodine copper(II) and bromine gold(II) and phosphorus lead(IV) and oxygen silver(I) and nitrogen copper(II) chloride Check your answers Transition Metal Answers iton(III) and phosphorus = FeP copper(II) and fluorine = CuF2 silver(I) and sulfur = Ag2S manganese(II) and nitrogen = Mn3N2 lead(IV) and iodine = PbI4 copper(II) and bromine = CuBr2 gold(II) and phosphorus = Au3P2 lead(IV) and oxygen = PbO2 silver(I) and nitrogen = Ag3N copper(II) chloride = CuCl2

Compounds containing POLYATOMIC ATOMS Polyatomic Ion: covalently bonded group of atoms that has a positive or negative charge and acts as a unit When you write formulas for compounds containing a polyatomic ion: Write the symbols for the metal and the polyatomic ion.* Write the valences as superscripts above each. Drop the + and - sign. Crisscross the valences so they become the subscript for the other element. If you have more than one of the polyatomic ion, you must encase it in parenthesis and place the subscript outside. You can only reduce a subscript outside the parenthesis of a polyatomic ion - you cannot change the formula the polyatomic ion. *In the case of ammonium (the only polyatomic cation) you would write it first and then the anion

Let me show you…

Let me show you…

Practice… Try these using a periodic table an a list of polyatomic ions. aluminum and sulfate ammonium and sulfur barium and hydroxide magnesium and phosphate lead(IV) and sulfite strontium and carbonate zinc(II) and phosphate ammonium and oxygen calcium and nitrate tungsten(II) and sulfate Check Answers Compounds with Polyatomic Ions Answers aluminum and sulfate = Al2(SO4)3 ammonium and sulfur = (NH4)2S barium and hydroxide = Ba(OH)2 magnesium and phosphate = Mg3(PO4)2 lead(IV) and sulfite = Pb(SO3)2 strontium and carbonate = SrCO3 zinc(II) and phosphate = Zn3(PO4)2 ammonium and oxygen = (NH4)2O calcium and nitrate = Ca(NO3)2 tungsten(II) and sulfate = WSO4

COVALENT FORMULAS: TWO NONMETALS Because covalent compounds share electrons they can share in different ways and can form many compounds between the same two elements. IMPORTANT: You never crisscross valences to determine covalent (two nonmetals) formulas. So just how do you write the formulas? Prefixes - that's how. Here are six covalent compounds that form between nitrogen and oxygen: nitrogen monoxide = NO nitrogen dioxide = NO2 dinitrogen oxide = N2O dinitrogen trioxide = N2O5 dinitrogen tetroxide = N2O4 dinitrogen pentoxide = N2O5 We saved the easiest formulas for last. In ionic compounds you always crisscross valences to determine the formulas. In covalent compounds atoms share electrons so there isn't any valence to crisscross. IMPORTANT: You never crisscross valences to determine covalent (two nonmetals) formulas. So just how do you write the formulas? Prefixes - that's how. Because covalent compounds share electrons they can share in different ways and can form many compounds between the same two elements. For example, you know two compounds that that exist between carbon and oxygen: CO carbon monoxide and CO2 carbon dioxide. The NAMES of covalent compounds contain prefixes that tell you how many atoms of each element is in the compound. Here are the prefixes used in covalent compounds:

Practice – Name these Go ahead and try these: Check your answers Just look at the name and you have the formula for a covalent compound. Go ahead and try these: sulfur dioxide dihydrogen oxide phosphorus pentafluoride carbon tetrachloride aluminum trichloride Check your answers Covalent Compounds Answers sulfur dioxide = SO2 dihydrogen oxide = H2O phosphorus pentafluoride = PF5 carbon tetrachloride = CCl4 aluminum trichloride = not possible. Never use prefixes in ionic compounds (contain a metal cation). This compound would simply be called aluminum chloride.

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6.4 Metallic Bonds How they form….common pool of electrons Metallic Lattice structure How they give metal its strength… Alloys…combined properties

POLYATOMIC ION: A covalently boned group of atoms that has a positive or negative charge and acts as a unit … ex. Iron (III) Oxide Fe(OH)3

Electronegativity

HOW DO THE ELECTRON CONFIGURATIONS CHANGE? ACROSS THE SAME PERIOD? DOWN THE SAME GROUP? 1. a. Describing Based on Table 1, how do the electron configurations of atoms within each period change as you go from lower to higher atomic number? How do the electron configurations change as you go across the table from one period to another within a row? b. Identifying Identify the number of valence electrons that characterize each of the four different periods shown in Table 1. c. Predicting In order to become more stable, predict whether atoms of elements in periods 1A and 2A in Table 1 would gain or lose electrons. Make a similar prediction about the atoms of elements in periods 6A and 7A in Table 1.

HOW DOES THE RADIUS OF AN ATOM CHANGE WHEN IT BECOMES AN ION? How does the radius change… When it becomes a cation? When it becomes an anion? Radius of the atom Charge of the ion (# electrons lost/gained) Radius of an ion of the atom 2. a. Comparing and Contrasting Check your predictions from question 1c by looking at Table 2 and finding the number of valence electrons gained or lost by atoms when they become ions. Compare periods 1A and 2A with periods 6A and 7A. For example, how many electrons are gained or lost by lithium (Li)? By oxygen (O)? b. Drawing Conclusions In general, how does an atom’s radius change when it becomes a cation? An anion? c. Predicting The last element in Period 1A is francium (Fr). It is not shown in either table. Predict how many valence electrons francium has, whether it gains or loses electrons to become an ion, and how its radius changes when it becomes an ion. Predict the radius change and # of valence electrons for Francium (Fr)

Not learned in this class….but interesting: hypo- and per- In the case where there is a series of four oxyanions, the hypo- and per- prefixes are used in conjunction with the -ite and -ate suffixes. The hypo- and per- prefixes indicate less oxygen and more oxygen, respectively. ClO- Hypochlorite ClO2- Chlorite ClO3- Chlorate ClO4- Perchlorate bi- and di- hydrogen Polyatomic anions sometimes gain one or more H+ ions to form anions of a lower charge. These ions are named by adding the word hydrogen or dihydrogen in front of the name of the anion. It is still common to see and use the older naming convention in which the prefix bi-is used to indicate the addition of a single hydrogen ion.HCO3- Hydrogen carbonate or bicarbonate HSO4- Hydrogen sulfate or bisulfate H2PO4- Dihydrogen phosphate