4.1 Ionic Bonding & Structure
Mrs. Page IB Chem Understandings Positive ions (cations) form by metals losingvalence electrons Negative ions (anions) form by non-metalsgaining electrons The number of electrons lost or gained isdetermined by the electron configuration of theatom The ionic bond is due to electrostatic attractionsbetween oppositely charged ions. Under normal conditions, ionic compounds areusually solids with lattice structures. Application & Skills Deduction of the formula and name of an ioniccompound from its component ions, includingpolyatomic ions Explanation of the physical properties of ioniccompounds (volatility, electrical conductivity, andsolubility) in terms of their structure. Nature of Science Use theories to explain natural phenomenon molten ionic compounds conduct electricity butsolid ionic compounds do not. The solubility andmelting points of ionic compounds can be usedto explain observations. Introduction to Bonding
Chemical bond: an interaction between atomsor ions that results in a reduction of thepotential energy of the system, therebybecoming more stable Three types of bonds: ionic, metallic, andcovalent The bond type depends on the atomselectronegativity values More Bonding Basics If the atoms have very differentelectronegativity values, then ionicbonding occurs If they both have high electronegativityvalues, then covalent bonding occurs If they both have low electronegativityvalues, then metallic bonding occurs Practice: What Kind of Bond?
Na and Cl Sr and O C and O Ni and Fe N and O Li and N Ti and Cr Ionic Covalent Metallic Valence Electrons Valence electrons are the electrons in theoutermost energy level, which is the highestoccupied energy level They are the electrons responsible for thechemical properties of atoms Electron transfers result in nobal gas electronconfigurations. Core electrons are those in the energy levelsbelow. Keeping Track of Electrons
Atoms in the same group have the sameouter electronic structure and thereforethe same number of valence electrons. The number of valence electrons iseasily determined. It is the groupnumber Group 2:Be, Mg, Ca, etc. Each has 2 valence electrons Electron Dot (Lewis Dot)diagrams
A way of showing & keeping track ofvalence electrons. Write the symbol - it represents thenucleus and inner (core) electrons Put one dot for each valence electron(8 maximum) First two electrons placed as a pair (sorbital) Then they dont pair up until they haveeach have 1 (Hunds rule) X The Electron Dot Diagram (Lewis Structure) for Nitrogen
Nitrogen has 5 valenceelectrons to show. First we write the symbol. N Place 1st pair Then add 1 electron at a time to each side. The Octet Rule The noble gases are unreactive in chemical reactions
In 1916, Gilbert Lewis used this fact toexplain why atoms form certain kinds ofions and molecules The Octet Rule: in forming compounds,atoms tend to achieve a noble gasstructure; 8 in the outer level is stable Each noble gas (except He, which has2) has 8 electrons in the outer level Formation of Cations Metals become oxidized (lose electrons) to attaina noble gas structure. They make positive ions (cations) If we look at the electronic structure, it makessense to lose electrons: Na:2, 8, 1 shows 1 valence electron Na1+: 2, 8This is a noble gas structure with 8electrons in the outer level. Electron Dots For Cations
Metals have few valence electrons (usually 3or less); calcium has only 2 valenceelectrons Ca Electron Dots For Cations
Metals will lose the valence electrons Ca Electron Dots For Cations
Form positive ions Ca2+ This is namedthe calciumion. No dots are now shown for the cation. Electron Configurations: Anions
Nonmetals are reduced (gain electrons)to attain noble gas electronicstructures. They make negative ions (anions) S = 2,8,6 = 6 valence electrons S2-= 2,8,8 = noble gas structure. Halide ions are ions from chlorine orother halogens that gain electrons Electron 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 phosphideion, and should show dots) Stable Electron Configurations
All atoms react to try and achieve a noble gasstructure. Noble gases have 8 valence electrons and so arealready stable This is the octet rule (8 in the outer level isparticularly stable). Ar Ionic Bonding Anions and cations are held together bythe electrostatic attraction due to theopposite charges (+ and -) Simplest ratio of elements in an ioniccompound is called the formula unit. The bond is formed through the transferof electrons (lose and gain) Electrons are transferred to achievenoble gas structure. Ionic Bonding Na Cl The metal (sodium)is oxidized (loses itsone electron) from the outer level. The nonmetal (chlorine) is reduced (gainsone electron) to fill its outer level, and willaccept the one electron that sodium is goingto lose. [ ] Cl - Na+ Ionic Bonding Notes:
[ ] Cl - Na+ Notes: Remember that no dots are now shown forthe cation Brackets must be shown in Lewisstructures to show overall charge of ion This step involving the formation of ions isa critical step to show in the formation ofionic bonds Ionic Bond Negative charges are attracted to positive charges.
Negative anions are attracted topositive cations. The result is an ionic bond. A three-dimensional crystal lattice ofanions and cations is formed. Ionic Compounds The ionic substance is held together bystrong electrostatic attractions in allthree dimensions No molecules present An ionic lattice-type structure isformed This gives them distinct physicalproperties NaCl CsCl TiO2 Properties of Ionic Compounds
Hard, brittle crystalline solids Relatively high melting and boilingpoints Do not conduct electricity whensolid, but do when molten or inaqueous solution Are more soluble in water than othersolvents - Page 198 The ions are free to move when they aremolten (or in aqueous solution), and thusthey are able to conduct the electric current. Preserve Electroneutrality
When ions combine, electroneutralitymust be preserved. In the formation of magnesiumchloride, 2 Cl- ions must balance a Mg2+ ion: Mg Cl- MgCl2 Predicting Ionic Charges
Group 1A: Lose 1 electron to form 1+ ions H+ Li+ Na+ K+ Rb+ Predicting Ionic Charges
Group 2: Loses 2 electrons to form 2+ ions Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Predicting Ionic Charges
Group 13: B3+ Al3+ Ga3+ Loses 3 electrons to form 3+ ions Predicting Ionic Charges
Nitride Group 15: P3- Phosphide As3- Arsenide Gains 3 electrons to form 3- ions Predicting Ionic Charges
Oxide Group 16: S2- Sulfide Se2- Selenide Gains 2 electrons to form 2- ions Predicting Ionic Charges
Group 17: F- Fluoride Br- Bromide Cl- Chloride I- Iodide Gains 1 electron to form 1- ions Predicting Ionic Charges
Stable noble gases do not form ions! Full octets. Group 18: Predicting Ionic Charges
Many transition elements have more than one possible oxidation state. Note the use of Romannumerals to show charges Iron (II) = Fe2+ Iron (III) = Fe3+ Polyatomic Ions (MUST KNOW!)
Because these are ions they also are involvedin ionic bonding! Ion Name NH4+ ammonium OH- Hydroxide NO3- Nitrate HCO3- Hydrogen Carbonate CO32- Carbonate SO42- Sulfate PO43- Phosphate Upcoming Dates: December 6 Final Exam Topics 1-3
HOMEWORK Read pp Upcoming Dates: December 6 FinalExam Topics 1-3