Chapter 4 Chemical Bonding: Chemical Bonding: Ionic Bond Model.
Chemical Bonding
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Transcript of Chemical Bonding
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Chemical BondingChapter 6
Pages 174-213(no Section 4)
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The The breakingbreaking of of bonds and the bonds and the
formingforming of bonds of bonds occur during occur during
chemical reactionschemical reactions..
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AspirinWhat is the
formula for a molecule of
aspirin?
What do we call the things that hold a molecule of aspirin together?
• C9H8O4
• covalent compound (made of all nonmetals - no ions)
Is it an ionic or covalent
(molecular) compound?
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Aspirin
• C9H8O4
• covalent compound (made of all nonmetals - no ions)
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Aspirin (Odyssey Program)
• C9H8O4
• covalent compound (made of all nonmetals - no ions)
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The Attachment Between Atoms
atoms combine to form
ionic bonds covalent bonds(M + NM) (NM + NM)
chemical bond – a mutual electrical attraction between the nuclei and valence electrons of two atoms that binds the atoms together
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Ionic Bonding• ionic bond – electrical attraction between
cations and anions; when electrons are taken by one atom from another atom
metal and a nonmetal
NaCl
cation and anion
(The charges are “hidden” to make a neutral compound.)
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1s
2s
2p
3s
1s
2s
2p
3s
Na 11e- F 9e-
Ionic Bonding: taking of electrons
Na+ 10e- STABLE!!! F- 10e- STABLE!!!
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I’m Positive!
A metal ionA metal atom A nonmetal atomA nonmetal ion
I’m Negative
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I’m Positive!
A metal ion A nonmetal ion
I’m Negative
When a metal and a nonmetal atom are around each other there is the opportunity for….
…the transfer of electrons producing ions that would like to cling to each other.
Ionic bonding!!!
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The simplest ratio of the packed ions is called:
The Formula Unit Ex: NaCl
“cubic”shape
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Ions
• Metals form cations.
(metals lose e-)
• Nonmetals form anions.
(nonmetals gain e-)
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Ions
• cations (+)• anions (-)
• monatomic ions – ions • formed from one atom Examples:
Na+ or O-2
• polyatomic ions - ions formed from two or more atoms bonded together
Examples: NH4+ or SO4
-2
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Naming Ions• monatomic ions
• cations – named like the atom, only add ion to it
» Example: Na+
is the sodium ion
• anions – remove the ending to the atom name and add –ide and ion to it
» Example: Cl-
is the chlorine
+ide ion
or the chloride ion
• polyatomic ions • You do not determine their names, you memorize them
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Ionic Compounds
• solid at room temperature (forming crystals)• high melting points (thus are usually solid at RT)• formula unit represents the lowest ratio of ions
that combine to form a neutral compound• when dissolved in water, the ionic compounds
will break up into ions (dissociate)• the solutions of ionic compounds will conduct
electricity (electrolytes)
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Dissociation
2H O(l) + -NaCl(s) Na (aq) + Cl (aq)
solid placed in water hydrated ions
(surrounded by water)
dissociation – when an ionic compound dissolves to break apart into hydrated ions
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Dissociation
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Electrolytes and Nonelectrolytes
When an ionic compound dissolves to produce ions, it is called an electrolyte because it conducts electricity in water.
When an compound does not dissolve to produce ions, it is called a nonelectrolyte because it does not conduct electricity in water.
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Electrolytes or salt?
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Check for Understanding
1. What kinds of atoms form ionic bonds?
2. What is a polyatomic ion?
3. Name 5 things you learned about ionic compounds.
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You Try It.
Do the Dissociation Equations worksheet.
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Covalent Bondingcovalent bond – when electrons are shared
between two atoms– the electronegativity difference between the
two atoms is less than 1.7– usually two nonmetals – NO ions formed! (no electrons are taken…just
shared)
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When a nonmetal and another nonmetal atom are around each other there is the opportunity for….
…the sharing of electrons producing molecules in which the atoms like to cling to each other.
Covalent bonding!!!
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The formation of a bond between two nonmetal atoms.
Atoms sufficiently far apart to have no interaction
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Figure 5 Page 179
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Covalent Compounds
• Also called molecular compounds• solid, liquid, or gas at room temperature• low melting points • molecular formula represents the actual ratio of
atoms that combine to form a neutral compound• when dissolved in water, the molecular
compounds DO NOT break up into ions
(NO dissociation)• the solutions of molecular compounds DO NOT
conduct electricity (nonelectrolytes)
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Pure Covalent
Ionic
The two fundamental
types of bonds.
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Pure Covalent
Ionic
There is another type of bond, not
purely covalent and not
purely ionic.
Polar Covalent
Nonpolar Covalent
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Sharing of Electrons
• How would you know if an electron is going to be taken by one atom from another?
• Is there ever a time in which the electron is not taken but shared?
• Is the electron always shared equally?
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Electronegativity
• electronegativity – a measure of the ability of an atom in a chemical compound to attract electrons from another atom in the compound
The difference in electronegativity values for two atoms will indicate whether the two atoms form an ionic bond (e- taken) or a polar or nonpolar covalent bond (e- shared).
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Electronegativity Differences• 0.0 to 0.4 nonpolar covalent
• 0.5 to 1.6 polar covalent
• 1.7 and up ionic
These ranges are flexible, although the general rule is a metal and nonmetal will
form an ionic bond and two nonmetals will form a covalent bond.(Learn these values!)
PS: They are different than your book!
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Ionic, Polar Covalent, or Nonpolar Covalent?
What kind of bond would each pair form?
1. N and S
2. S and C
3. Mg and Cl
4. C and F
5. Ba and O
Which one of these bonds has the least ionic character?
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Valence Electrons
• valence electrons – the electrons in the highest energy level
Na: 1s22s22p63s1 - 1 valence e-
O: ? Ne: ? Al: ? He: ?
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Octet Rule• octet rule – most atoms will gain or lose
electrons to have 8 valence electrons (e- in the highest energy level)– Exceptions: H, He, Li, Be, B, and some atoms
P and higher on the periodic table
Why is an atom like Ca more stable once it becomes an ion?
How many valence electrons would calcium have to lose to have 8?
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VSEPR Theory
Valence
Shell
Electron
Pair
Repulsion Theory
Repulsion between the sets of valence-level electrons
surrounding an atom causes these sets to be oriented as far
apart as possible.
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Regions of Electron Density
What is a Region of electron density?
• Single bond (2e- connecting 2 atoms)
• Double bond (4e- connecting 2 atoms)
• Triple bond (6e- connecting 2 atoms)
• Lone pair (unbonded pair) (2e- alone on an atom)
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LINEAR180o
2 Regions of Electron Density2 Bonds
bonded pair of electrons
bonded pair of electrons
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TRIGONAL PLANAR120o
3 Regions of Electron Density3 Bonds
3 bonded pairs of electrons
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BENT119o
3 Regions of Electron Density2 Bonds & 1 Lone Pair
2 bonded pairs of electrons 1 lone pair
of electrons
You don’t have to know this!
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TETRAHEDRAL109.5o
4 Regions of Electron Density4 Bonds
4 bonded pairs of electrons
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TRIGONAL PYRAMIDAL107o
4 Regions of Electron Density3 Bonds & 1 Lone Pair
3 bonded pairs of electrons
1 lone pair of electrons
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BENT105o
4 Regions of Electron Density2 Bonds & 2 Lone Pairs
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All of these have 4 regions of electron density
(although the number of bonded pairs is different)
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TRIGONAL BIPYRAMIDAL120o & 90o
5 Regions of Electron Density5 Bonds
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SEE-SAW120o & 90o
5 Regions of Electron Density4 Bonds & 1 Lone Pair
You don’t have to know this!
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T-SHAPED120o & 90o
5 Regions of Electron Density3 Bonds & 2 Lone Pairs
You don’t have to know this!
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LINEAR180o
5 Regions of Electron Density2 Bonds & 3 Lone Pairs
You don’t have to know this!
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OCTAHEDRAL90o
6 Regions of Electron Density6 Bonds
SF6
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SQUARE PYRAMIDALapproximately 90o
6 Regions of Electron Density5 Bonds & 1 Lone Pair
You don’t have to know this!
BrF5
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ICl4-
SQUARE PLANAR90o
6 Regions of Electron Density4 Bonds & 2 Lone Pairs