section 2.6: molecular and ionic compounds by doba jackson, ph.d
TRANSCRIPT
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Section 2.6: Molecular and Ionic Compounds
By Doba Jackson, Ph.D.
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Molecules, Ions, and Chemical Bonds
Covalent Bond: A bond that results from the sharing of electrons between atoms.
Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.
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Definitions of Molecules, Ions, and Chemical Bonds
Ionic Bond: An electrostatic attraction between charged particles. Typically a metal bonded to a nonmetal.
Ion: A charged atom or molecule.
Cation: A positively charged particle. Most cations are metals.
Anion: A negatively charged particle. Nonmetals tend to form anions.
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Ions, and Chemical Bonds
In the formation of sodium chloride, one electron is transferred from the sodium atom to a chlorine atom.
Na+1 + Cl-1Na + Cl2
11 protons10 electrons
17 protons18 electrons
11 protons11 electrons
17 protons17 electrons
1
2
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Evidence for existence of ions
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We can predict many element’s ionic charge based on its location on the
periodic table
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Naming Ionic Compounds
+1+2 +3 -3 -2 -1Naming (IUPAC)
Cation Anion
Na+1 Cl-1
Sodium Chloride
Metals tend to form Cations
Nonmetals tend to form Anions
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Naming Ionic Compounds
Ionic Compound: A neutral compound in which the total number of positive charges must equal the total number of negative charges.
Some binary Ionic Compounds
Cation – Anion(ide) Cation AnionIonic
Compound
cation anion(ide) C+x A-y CyAx
aluminum sulfide: Al2S3Al+3 S-2
sodium chloride NaClNa+1 Cl-1
magnesium oxide MgOMg+2 O-2
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Determine the charge on each ionic compound and name the compound
MgS
BaF2
AlP
Ga2O3
Li2O
Mg3N2
CaS
Fe+3 O-2
Pb+4 O-2
Ni+2 Br-1
Manganese (IV) Oxide
Tungsten (VI) bromide
Mg+2
Ba+2
Al+3
Ga+3
Li+1
Mg+2
Ca+2
Mn+4
W+6
S-2
F-1
P-3
O-2
O-2
N-3
S-2
O-2
Br-1
Magnesium sulfide
Barium flouride
Aluminum Phosphide
Gallium oxideLithium oxide
Magnesium nitride
Calcium sulfide
Iron (III) oxide
Lead (IV) oxide
Nickel Bromide
Fe2O3
PbO2
NiBr2
MnO2
WBr6
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Some transition metals have more than one stable charge
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What happens when the cation has more than one oxidation state
Some binary Ionic Compounds
Cation Anion(ide) Cation AnionIonic
Compound
cation (x) anion(ide) C+x A-y CyAx
lead (II) flouride PbF2Pb+2 F-1
iron (III) oxide Fe2O3Fe+3 O-2
tin (II) chloride SnCl2Sn+2 Cl-1
Use Roman numerals in parentheses to indicate the charge on metals that form more than one kind of cation.
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Molecules, Ions, and Chemical Bonds
Covalent Bond: A bond that results from the sharing of electrons between atoms.
Ionic Bond: A bond that results from oppositely charged ions that are electrostaticlly attracted to each other.
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Definitions of Ionic and Covalent compounds
• Ionic bonds are a result of a combination of a metal (electropositive element) and a non-metal (electronegative element).
• In ionic bonds, atoms are attracted to each other by opposite charges.
• Covalent bonds are a result of the combination of two non-metals (two electronegative elements).
• In covalent bonds, atoms are attracted to each other by a shared pair of electrons.
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A Comparison of Ionic and Covalent Bonds
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Points to consider: Ionic verses Covalent compounds
Point 1: Ionic compounds are usually solids (when pure)
Point 2: Ionic compounds have very high boiling and
melting points
Point 3: Covalent compounds can be either solids, liquids
or gases
Point 4: Covalent compounds have relatively lower boiling
and melting points
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Why does NaCl have such high boiling and melting points?
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A chemical representation of a covalent compound (ethanol)
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Predict whether each compound is an ionic or molecular compound.
• KI, component in table salt
• H2O2, antioxidant
• CHCl3, anesthetic
• Li2CO3, antidepressants
Ionic: 1 metal 1 nonmetal
Molecular: 2 nonmetals
Molecular: 3 nonmetals
Ionic: 1 metal 2 nonmetals
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To name nonmetals, we first have to understand a concept called Electronegativity
Electronegativity: The ability of an atom in a molecule to attract the shared electrons in a covalent bond.
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Naming Covalent Compounds: Must know these prefixes
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Choose which compound is more electronegative, then change the suffix to -ide
- Write the name: electropositive - electronegative
- Add the suffix “ide” to the end of the electronegative atom.
- Use the prefixes to indicate the multiplicity of the both atoms.
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Example: naming N2O4
N2O4
The second element (Oxygen) is more electronegative and takes the name of the element with an “ide” modification to the ending.
The first element (Nitrogen) is more electropositive and takes the name of the element.
The prefix is added to the front of each to indicate the number of each atom.
dinitrogen tetraoxide
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WORKED EXAMPLE
Give systematic names for the following compounds
Solution(a) PCl3
(b) N2O3
(c) P4O7
(d) BrF3
Phosphorus trichloride
Dinitrogen trioxide
Tetraphosphorus heptoxide
Bromine trifluoride