Chapter Four

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Chapter Four

• Ionic Compounds

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Ions

• When an element loses or gains electrons, the net
  charge is no longer zero.
• A cation (positive ion) is formed when an
  element loses electrons
• An anion (negative ion) is formed when an
  element gains electrons

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Periodic Trends (Periodicity)

• Atomic Radius
• Elements get larger going down a column
• Elements get smaller going across a row

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Periodic Trends

• Ionization Energy (cation formation)
• Decreases going down a column
• Increases going across a row
• Electron Affinity (anion formation)
• Decreases going down a column
• Increases across a row

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Ionic Bonds

• Electrons are transferred from an element with
  low ionization energy to elements with high
  electron affinity.
• Na transfers an electron to Cl to form NaCl.
• This results in a crystal structure with the same
  number of sodium and chloride ions and thus we
  say the formula is NaCl.

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Properties of Ionic Compounds

• Soluble in water
• Conduct electricity
• High melting points
• Crystalline

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Ions and the Octet Rule

• Elements gain or lose electrons in order to
  attain a full valence shell. (The configuration
  of the noble gases)
• We will assume that the elements all obey an
  octet rule (8 electrons in the valence shell)
  except for hydrogen (2 electrons)

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Ionic Compound Formation

• Elements will form ions using the octet rule.
• Find the Group Number at the top of the column.
• If there are less than 4 electrons in outer
  shell, the atom will lose electrons and the ion
  will be positive.
• If there are more than 4 electrons in outer
  shell, the atom will gain electrons and the ion
  will be negative.

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Group IA Alkali Metals

• One valence electron
• Always 1 ions
• Na gt Na 1e-

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Group IIA Alkaline Earth Metals

• Two valence electrons
• Always 2 ions
• Mg gt Mg 2 2 e-

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Group IIIA

• Three valence electrons
• Always 3 ions
• Al gt Al 3 3e-

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Group VA

• Five valence electrons
• Gains 3 electrons to form 3 ions
• N 3 e- ? N3-
• N lt N3-

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Group VIA

• Six valence electrons
• Gains two electrons to form 2 ions
• O 2 e- ? O2-
• O lt O2-

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Group VIIA - Halogens

• Seven valence electrons
• Gains one electron to form 1 ions
• Cl 1e- ? Cl-
• Cl lt Cl-

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Group VIIIA Noble Gases

• Eight valence electrons
• Cannot gain or lose electrons
• Chemically inert

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Stable Noble Gas Configuation

• Ions form with the same number of electrons as
  the noble gases.
• Na (11 electrons) gt Na (10 electrons)
• Mg (12 electrons) gt Mg 2 (10 electrons)
• O (8 electrons) gt O2- (10 electrons)
• F (9 electrons) gt F- (10 electrons)

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Isoelectronic Series

• Ions form with Noble gas configurations
• The ions with 10 electrons are
• N3- O2- F- Ne Na Mg2 Al3
• What are the members of the argon isoelectronic
  series?

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Lewis Structures

• We indicate the number of valence electrons using
  a Lewis Structure
• There are four sides around the symbol
• Each side can hold two electrons
• There are a total of eight around the symbol

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Polyatomic Ions

• NH4 ammonium ion
• H3O hydronium ion
• OH- hydroxide ion
• NO3- nitrate ion
• CH3COO- acetate ion (C2H3O2-)
• HCO3- bicarbonate ion

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• CO32- carbonate ion
• SO42- sulfate ion
• HPO42- (mono)hydrogen phosphate ion
• H2PO4- dihydrogen phosphate ion
• PO43- phosphate ion

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Formulas for Ionic Compounds

• Formula must be electrically neutral
• The number of positive charges must equal the
  number of negative charges
• The subscripts tell how many of each atom are in
  the formula

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0

• Sodium and Chlorine
• NaCl
• Calcium and Chlorine
• CaCl2
• Aluminum and Chlorine
• AlCl3

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0

• Sodium and Sulfate (SO42-)
• Na2SO4
• Magnesium and Hydroxide
• Mg(OH)2
• Barium and Nitrate
• Ba(NO3)2

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• Potassium and Phosphate
• K3PO4
• Magnesium and Phosphate
• Mg3(PO4)2
• Sodium and Bicarbonate
• NaHCO3

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• Ammonium and Acetate
• NH4CH3COO
• Sodium and Carbonate
• Na2CO3
• Sodium and Oxygen
• Na2O

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Nomenclature

• Find position of first element on Periodic Table
• Metal with constant charge (Group IA, IIA, Al,
  Ag, Zn, Cd, and NH4
• Transition Metal with variable charge
• Non-Metal

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Metals with Constant Charge

• Cation is named as element. Anion is named by
  changing ending to ide
• NaCl sodium chloride
• MgCl2 magnesium chloride
• Na2O sodium oxide
• Mg3N2 magnesium nitride
• (NH4)2CO3 ammonium carbonate

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Transition Metals

• Roman numerals are used to designate charge on
  cation
• FeCl2 iron(II) chloride (ferrous)
• FeCl3 iron(III) chloride (ferric)
• Cu2CO3 copper(I) carbonate (cuprous)
• CuO copper(II) oxide (cupric)

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Non-Metals

• Prefixes are used to tell how many of each atom
  are present in formula
• 1-mono 6-hexa
• 2-di 7-hepta
• 3-tri 8-octa
• 4-tetra 9-nona
• 5-penta 10-deca

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• CO carbon monoxide
• CO2 carbon dioxide
• CCl4 carbon tetrachloride
• XeF6 xenon hexafluoride

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Acids and Bases

• Acid A substance that donates protons (H) in
  water
• Common Acids
• acetic, CH3COOH
• carbonic, H2CO3
• hydrochloric, HCl
• nitric, HNO3
• phosphoric, H3PO4
• sulfuric, H2SO4

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• Base A substance that provides hydroxide ion
  (OH-) in solution
• Common Bases
• Sodium hydroxide, NaOH
• Potassium hydroxide, KOH
• Barium hydroxide, Ba(OH)2

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Dissociation in Water

• Soluble substance dissolve in water by
  dissociation
• NaCl gt Na Cl-
• CaCl2 gt Ca2 2Cl-
• HCl gt H Cl-
• NaOH gt Na OH-