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1Tuesday!!!!!1/24/12
Bell Ringer
• 1. Pick up the Ionic bond packet off the front demo table. Write down and answer the following questions on your packet somewhere.• A. Identify the valence
electrons and electron dot drawing of the following elements:
• Li Ca Al
• C P S
• F Ne
Schedule
1.Bell Ringer
2. Ionic & Covalent Bonding Demo
3. Ionic/Covalent Bonding Notes
HOMEWORK: Practice problems in your packet
Chemistry
I CAN… compare and diagram ionic and covalent bonding.
4
Bonding
• Chemical Bond
–attractive force between atoms or ions that binds them together as a unit
–bonds form in order to…» decrease potential energy (PE)» increase stability
5Intra VS Intermolecular Forces• INTRA within• INTER between, among
• Intramolecular force: bonds between atoms or ions in molecules Examples: metallic, covalent, & ionic bonds
– Hydrogen bonds to oxygen and forms water
• Intermolecular force: attraction between molecules themselves Intermolecular forces are only associated with covalently bonded molecules (glucose & fructose hydrogen bridge to make sucrose)
• 3 different levels of strength:• 1) Hydrogen Bridge (used to be called H bond) (strongest)• 2) Dipole-dipole forces• 3) London Dispersion forces (weakest) (covalently bonded molecules have this)
– Water molecule attracted to another water molecule
6Review of Chemical Review of Chemical BondsBonds
• There are 2 main types of There are 2 main types of bonding:bonding:
• IONICIONIC——transfer transfer of 1 or more of 1 or more valence electrons valence electrons
• COVALENTCOVALENT——sharingsharing of valence of valence electronselectrons
““Between ionic Between ionic and covalent and covalent most bonds are”most bonds are”
7The type of bond can The type of bond can usuallyusually be calculated by be calculated by finding the difference in electronegativity of finding the difference in electronegativity of
the two atoms that are going together.the two atoms that are going together.
8Electronegativity Difference
• If the difference in electronegativities is between:
– 1.7 to 4.0: Ionic
– 0.3 to 1.7: Polar Covalent
– 0.0 to 0.3: Non-Polar Covalent
Example: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!
9
Ionic BondsIonic BondsIons are positively or negatively
charged atoms due to the removal or addition of an ELECTRON
1. CATION (CAT – ION) is positively charged – electron removed.
2. ANION (AN – ION) is negatively charged – electron gained.
In generalIn general
• metals (Mg) lose electrons --->
cations (+)
• nonmetals (F) gain electrons --->
anions (-)
10
Ionic BondsIonic BondsIonic BondsIonic Bonds
Positive cations and the negative Positive cations and the negative anions are attracted to one another anions are attracted to one another (remember: Opposites Attract!)(remember: Opposites Attract!)
Therefore, ionic Therefore, ionic compounds are usually compounds are usually between metals and between metals and nonmetals (opposite ends nonmetals (opposite ends of the periodic table).of the periodic table).
11Comparison
Ionic Compounds
• Crystalline solids (made of ions)
• High melting and boiling points
• Conduct electricity when melted
• Many soluble in water but not in nonpolar liquid
• Metal and nonmetals bond
Covalent Compounds
• Gases, liquids, or solids (made of molecules)
• Low melting and boiling points
• Poor electrical conductors in all phases
• Many soluble in nonpolar liquids but not in water
• Nonmetals bond with other nonmetals
15
A chemical bond in which two or more electrons are shared by two atoms.
How should two atoms share electrons?
F F+
7e- 7e-
F F
8e- 8e-
F F
F F
Lewis structure of F2
lone pairslone pairs
lone pairslone pairs
single covalent bond
single covalent bond
Covalent Bond
16
8e-
H HO+ + OH H O HHor
2e- 2e-
Lewis structure of water
Double bond – two atoms share two pairs of electrons
single covalent bonds
O C O or O C O
8e- 8e-8e-double bonds double bonds
Triple bond – two atoms share three pairs of electrons
N N8e-8e-
N N
triple bondtriple bond
or
17PolarityPolarity
AA molecule, such as HF, that has a center of molecule, such as HF, that has a center of positive charge and a center of negative positive charge and a center of negative charge is said to be polar, or to have a dipole charge is said to be polar, or to have a dipole moment.moment.
+
FH
18
Dipole Moment
• Direction of the polar bond in a molecule.
• Arrow points toward the more electronegative atom.
H Cl + - Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
19
H F
FH
Electrons are shared unequally
A covalent bond with greater electron density around one of the two atoms resulting in partial charges (dipole)
electron richregionelectron poor
region
e- riche- poor
+ -
Polar Covalent Bond
20
Bond PolarityBond PolarityBond PolarityBond PolarityHCl is HCl is POLARPOLAR because it because it
has a positive end and a has a positive end and a negative end. (difference negative end. (difference in electronegativity)in electronegativity)
Cl has a greater share in Cl has a greater share in bonding electrons than bonding electrons than does H.does H.
Cl has a greater share in Cl has a greater share in bonding electrons than bonding electrons than does H.does H.
Cl has slight negative charge Cl has slight negative charge (-(-)) and H has and H has slight positive charge slight positive charge (+ (+ ))
H Cl••
••
+ -••H Cl
••
••
+ -••
21
• This is why oil and water will not mix! Oil This is why oil and water will not mix! Oil is nonpolar, and water is polar.is nonpolar, and water is polar.
• The two will repel each other, and so you The two will repel each other, and so you can not dissolve one in the othercan not dissolve one in the other
Bond PolarityBond PolarityBond PolarityBond Polarity
22
Bond PolarityBond PolarityBond PolarityBond Polarity
• ““Like Dissolves Like”Like Dissolves Like”
–Polar dissolves PolarPolar dissolves Polar
–Nonpolar dissolves Nonpolar dissolves NonpolarNonpolar
23
Determining Molecular Polarity
• Nonpolar Molecules
-Electrons are shared equally-Symmetrical electron density-Often identical atoms-Dipole moments are symmetrical and cancel out.
BF3
F
F F
24
......
Polar Bonds
H Cl
Polar
A molecule has a zero dipole moment because their dipoles cancel one another.
H HO
PolarF F
B
F
Nonpolar
HH
H
N
Polar
Polar Nonpolar
F FCl
F
F F
Xe
F FCl
ClC
Cl
Nonpolar Polar
Cl
HC
Cl
H
H
25
Hydrogen Bonding
• Occurs with polar structures only
• Includes a positive Hydrogen ion bonding directly to a negative ion
• Examples: H-O H-N H-F H2O
• DNA, RNA, and enzymes have many Hydrogen bonding sites
• Strongest intermolecular force
26
London Dispersion forces
• Also known as van der Waals bonds
• Occur only with nonpolar structures
• Weakest intermolecular force
• Electrostatic bonds between atoms or molecules
• Temporary dipole moment
28Double and Double and even triple even triple bonds are bonds are commonly commonly observed for C, observed for C, N, P, O, and SN, P, O, and S
••O OC
•• ••
••
••O OC
•• ••
••
HH22COCO
SOSO33
CC22FF44
29
1/25/10MONDAY
• Bell Ringer:
–Pick up the Molecular Geometry packet off the front green demo table.
–Remember, we needs Dots candy and toothpicks if you want to perform the edible lab
31
VSEPRVSEPR • VValence alence SShell hell EElectron lectron PPair air
RRepulsion theory.epulsion theory.
• Most important factor in Most important factor in determining geometry is determining geometry is relative relative repulsion between repulsion between electron pairs.electron pairs.
Molecule adopts Molecule adopts the shape that the shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.
Molecule adopts Molecule adopts the shape that the shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.
MOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRYMOLECULAR GEOMETRY
32
Some Common GeometriesSome Common Geometries
LinearLinear
Trigonal PlanarTrigonal Planar TetrahedralTetrahedral
35
Structure Determination by Structure Determination by VSEPRVSEPR
Structure Determination by Structure Determination by VSEPRVSEPR
Water, HWater, H22OOThe electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL
The molecular The molecular geometry is geometry is BENTBENT..
The molecular The molecular geometry is geometry is BENTBENT..
H O H••
••
H O H••
••
2 bond 2 bond pairspairs
2 lone 2 lone pairspairs
36
Structure Structure Determination by Determination by
VSEPRVSEPR
Structure Structure Determination by Determination by
VSEPRVSEPRAmmonia, NHAmmonia, NH33
The electron pair geometry is tetrahedral.The electron pair geometry is tetrahedral.
H
H
H
lone pair of electronsin tetrahedral position
N
The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..
The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..