Chapter 3 lecture

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ch 3 lecture

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  • 1. 1/30/13CHM 101 Ch 3: Ionic Compounds Key Vocabulary Terms •Ion – a charged atom •Cation – a positively (+) charged ion •Anion – a negatively (-) charged ion
  • 2. Ionic Compounds Noble gases typically do not form ions or bonds. Why?Octet RuleAn octet is 8 valence electrons, and is associated with the stability of the noble gases.(Exception: He is stable with 2 valence electrons (duet).) valence electrons He 1s2 2 Ne 1s2 2s2 2p6 8 Ar 1s2 2s2 2p6 3s2 3p6 8 Kr 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 8
  • 3. Chemical BondingOctet RuleAtoms form octets to become more stable. • They do this by losing, gaining, or sharing valence electrons. • In the process, they form ionic bonds or covalent bonds.
  • 4. Chemical BondingIonic compound – compound consisting of negatively and positively charged ions. Electrons are not shared between the ions. They are transferred from atoms of one element to atoms of another element. NaCl, MgBr2, KI, etc. Ionic compounds are usually composed of a metal and a nonmetalCovalent compound – compound consisting of atoms of different elements that share electrons in covalent bonds. H2O, CCl4, C6H12O6, etc. Covalent compounds are usually composed of only nonmetals
  • 5. Chemical BondingIdentify the following compounds as ionic or covalent: a. Na2S Ionic b. CuCl2 Ionic c. CH4 Covalent d. PCl3 Covalent
  • 6. Ionic CompoundsFormation of a Sodium Ion, Na+ With the loss of its valence electron, the sodium ion has a +1 charge. Sodium atom Sodium ion 11p+ 11p+ 11e- 10e- 0 1+ 1s2 2s2 2p6 3s1 1s2 2s2 2p6 Sodium achieves an octet by losing its one valence electron.
  • 7. Ionic CompoundsFormation of Magnesium Ion, Mg2+ With the loss of two valence electrons, magnesium forms a positive ion with a +2 charge. Mg atom Mg2+ ion 12p+ 12p+ 12e- 10e- 0 2+1s2 2s2 2p6 3s2 1s2 2s2 2p6 Magnesium achieves an octet by losing its two valence electrons.
  • 8. Ionic CompoundsMetals Form Positive Ions Metals form cations (positive ions) by losing one or more of their valence electrons to have the electron configuration of the nearest noble gas. The ions have fewer electrons than protons. Group 1A metals → ion 1+ Group 2A metals → ion 2+ Group 3A metals → ion 3+
  • 9. Ionic CompoundsFormation of a Chloride Ion, Cl– By gaining one electron, the chloride ion has a -1 charge. Chlorine atom Chloride ion 17p+ 17p+ 17e- 18e- 0 1–1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6 Chlorine achieves an octet by adding an electron to its valence electrons.
  • 10. Ionic CompoundsFormation of Negative Ions Nonmetals form anions (negative ions) by gaining one or more electrons to have the electron configuration of the nearest noble gas. The ions formed have more electrons than protons. Group 6A nonmetals → ion 2− Group 7A nonmetals → ion −
  • 11. ElectronegativityWhat property determines which atoms will loseelectrons and which atoms will gain electrons? ELECTRONEGATIVITY!
  • 12. Electronegativity• Electronegativity is a measure of an atom’s tendency to attract electrons Increasing Increasing
  • 13. Ionic CompoundsMain Group Ions – You must know these charges.
  • 14. Ionic CompoundsOther ions – You must know these charges. Some metals have more than one charge when they form cations.
  • 15. Ionic CompoundsIonic compounds consist of positive and negative ions (very often metal cation and nonmetal anion. Sodium chloride (NaCl) or “table salt” is an example of an ionic compound.
  • 16. Ionic CompoundsAn ionic formula has charge balance. total positive charge = total negative charge The symbol of the cation is written first followed by the symbol of the anion. How many anions do you need for each cation? In sodium chloride, we need one chloride ion for each sodium ion. Formula: NaCl We use subscripts to describe the number of ions. No subscript means “one”.
  • 17. Ionic CompoundsCharge Balance In MgCl2 In magnesium chloride, we need two chloride ions for each magnesium ion. We use subscripts to describe the number of ions. Formula: MgCl2
  • 18. Ionic CompoundsWriting Ionic Formulas Let’s make an ionic compound from these ions: Na+ and N3−. For each nitride ion, N3-, how many sodium ions, Na+, do we need? How do we write the formula? Practice: Write a formula for an ionic compound made of Ba 2+ and Cl-. Practice: Write a formula for an ionic compound made of Pb4+ and O2-.
  • 19. Ionic CompoundsRules for Naming Ionic Compounds 1. The name of the cation comes first, then the name of the anion. 2. For metals that only form 1 cation, the cation name is the same as the metal name. Ca2+ - calcium ion 3. For metals that can form more than 1 cation, the charge is indicated with Roman numerals. Fe2+ - iron (II) Fe3+ - iron (III) 4. Monatomic anions are named by adding –ide to the root name. O2− - oxide F− - fluoride
  • 20. Ionic CompoundsRules for Naming Ionic Compounds Metal cation name is same as Nonmetal anion name changes element name element ending to –ide.
  • 21. Ionic CompoundsWrite names for the following ionic compounds: a. MgS b. FeCl2 c. SnF2 d. Cr2O3
  • 22. Ionic CompoundsGuide to Writing Formulas from the Name 1. Identify the cation and the anion. 2. Determine their charges (the Roman numeral gives the charge.) 3. Balance the charges. 4. Write the formula with the cation first, use subscripts to indicate the number of each ion. Write the formula for lead (II) fluoride.
  • 23. Ionic CompoundsPolyatomic IonsA polyatomic ion is a molecularunit of atoms with an overallionic charge. **You MUST know these names and formulas!**
  • 24. Ionic CompoundsNaming Compounds with Polyatomic Ions The cation is named first followed by the name of the polyatomic ion. NaNO3 sodium nitrate K2SO4 ? Fe(HCO3)3 ? (NH4)3PO4 ?
  • 25. Ionic CompoundsWriting Formulas with Polyatomic Ions The formula of an ionic compound containing a polyatomic ion must have a charge balance that equals zero (0). Na+ and NO3− : NaNO3 If there are two or more polyatomic ions they must be in parentheses. Use subscripts to indicate how many are present. Mg2+ and 2NO3− : Mg(NO3)2 subscript 2 for charge balance Practice: Write the formula for chromium (II) hydroxide.
  • 26. Ionic CompoundsUse the table below to quiz yourself. Use the formula, write the name.Use the name, write the formula.
  • 27. Ionic CompoundsProperties of Ionic Compounds H2 O In solid ionic compounds, When dissolved in water, ions the ions are held rigidly in dissociate, dispersing (+) and (–) place. charged ions in solution. KBr (s) K+ (aq) + Br- (aq) Ionic compounds are electrolytes – substances that conduct electricity when dissolved in water.
  • 28. Ionic Compounds No current in distilled water.
  • 29. Ionic Compounds No current in solid ionic compound.
  • 30. Ionic Compounds Current!!!
  • 31. Covalent compounds do not dissociate into ions when dissolved in water. Therefore, they are nonelectrolytes. C6H12O6 (s) C6H12O6 (aq)
  • 32. Ionic CompoundsMolecular vs. Ionic Compounds