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Chapter 3 – Elements Combine to Form Compounds
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Ion Charge or Combining CapacityRevisited
• The number of bonds an atom wants to form– Determined by the number of e- in the
outer shell that an element wants to donate or borrow.
Example:– Ca = +2 – Na = +1– Cl = -1
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Metals vs. Nonmetals
• Metals have positive (+) charges.– Therefore, they want to donate an e- from
their outer shells.
• Most non-metals have negative (–) charges.– Therefore, they want to accept an e- into
their outer shells.
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Ionic Compounds
• Atoms gain or lose electrons and form ions.• The charges of the ions are attracted to the
opposite charge; therefore a compound is produced.
Example: Na and Cl combine to form NaCl
NOTE: In covalent compounds, atoms combine by sharing electrons to form molecules.
Example: C and O share electrons to form CO
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Ionic Bonds
• Lead to the formation of crystal lattices.• All the ions are attracted to all other ions in
the crystal, although nearest ions have the greatest attraction.
• Repeating pattern of negative and positive charges.
• Think in terms of ratios. NaCl is a ratio of one sodium to one chlorine, but many NaCl will form a crystal lattice.
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Two Representations of Crystal Lattices
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Rules for Naming IonicChemical Compounds
1. Write the name of the metal element 1st
2. Write the name of the non-metallic element 2nd (is farther right on the Periodic Table)
3. Change the ending of the non-metallic element to “ide”
Example: CaCl2
Calcium chloride
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Chemical Formulas of Ionic Compounds
• Formulas contain symbols to identify each ion in an ionic compound, as well as the relative numbers of ions in the compound.
Example: NaCl – 1 sodium:1chlorine
CaF2 – 1 calcium:2 fluorines
Note: Relative numbers of each ion is a subscript to the right of the symbol
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Rules for Writing Ionic Chemical Formulas
1. Write the symbol of the metal 1st
2. Write the symbol of the non-metal 2nd
3. Write in the ion charges of both symbols as superscripts to the top right of each symbol (found on the Periodic Table)
4. Drop the +/- signs and cross the ion charges and write as subscripts (to the bottom right of the symbol). The number 1 is never written.
5. Reduce, if necessary
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Example of a Metal & Non-metal Combining
1. Calcium chloride (write the symbols)
2. Ca Cl (superscript combining capacities)
3. Ca 2+ Cl 1-
4. Ca 2+ Cl 1-(drop the +/- signs and cross combining capacities)
5. CaCl2
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Compounds Containing Multivalent Metals
• Notice that some metallic elements have more than 1 ion charge.
• We need to use Roman Numerals to indicate which combining capacity is used.
• E.g. Copper (II) chloride = Cu +2
• E.g. Copper (I) chloride = Cu +1
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Naming Note: Multivalent Metal
Use the Roman Numeral equal to the ionic charge to indicate which combining capacity was used
E.g. CuCl2
Cu1+ or Cu2+
Copper (II) chloride
E.g. Fe2O3
Fe3+ or Fe2+
Iron (III) oxide
You need to reverse cross to find combining capacities.
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Reactions involving Polyatomic Ions (Radicals)
• E.g. Ammonium sulfide
• Ammonium = NH4 1+ (1+ is the ion charge)
(given on the back of the Periodic Table)
• When NH4 1+ S 2- combine, the NH4 stays together
• So, NH4 1+ S 2-
• You need to put brackets around NH4 so you can separate the digits
• (NH4)2 S
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Naming Note: Polyatomic Ions
• Write the metal name first.
• Write the name of the polyatomic ion; do not change using “ide”.
Example: Sodium combines with cyanide
NaCN
Sodium cyanide
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Radicals & Roman Numerals
• Copper sulfate
• Copper (II) sulfate
1.Cu SO4
2.Cu2+ SO4
2-
3.Cu2+ SO4
2-
4.Cu2(SO4)2 the 2’s reduce
5.Cu(SO4) brackets can be dropped
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Types of Chemical Reactions
• Exothermic – energy is released from the reaction
Example: Atomic blast
• Memory Tip:– Exo – starts with the
letters “ex” similar to exit
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Types of Chemical Reactions
• Endothermic – energy is absorbed in order for the reaction to occur
Example: cooking eggs
• Memory Tip:– Endo – starts with the
letters “en” similar to enter