vsepr theory: molecular shapes most shapes are based on a __________________. examples: ch 4 ccl 4...
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VSEPR Theory: Molecular Shapes
• Most shapes are based on a __________________.
Examples: CH4 CCl4
• Removing the top of the tetrahedral makes the ________________ shape.
Examples: NH3 PCl3
tetrahedral
pyramidal
VSEPR Theory: Molecular Shapes
• Removing one side of the pyramid makes the _____________ shape.
Examples: H2O H2S
• If there are only two atoms bonded, it is ______________.
Examples: O2 HCl CO2 (linear because of its double bonds.)
bent
linear
VSEPR Theory: Molecular Shapes
•Another we will need to know is called “trigonal planar”. “Trigonal” means that the central atom is bonded to ___ other atoms. “Planar” means that the 3 atoms all lie in the same ______________.
Example: BF3
• (Notice that Boron will only have ___ e-’s around it. The missing pair of electrons will make it planar instead of ________________.)
3plane
6pyramidal
VSEPR Theory: Molecular Shapes
• Finally, the last 2 shapes occur when there are 5 or 6 regions of electrons are around the central atom. (These molecules are also exceptions to the octet rule!)
-___________________ (5 electron domains)
-__________________ (6 electron domains)
Examples: PCl5 and SF6
Trigonal bipyramid
Octahedral
Polar and Nonpolar Bonds
• Even though the electrons in a covalent bond are shared, sometimes the attraction for the bonded pair, (the _____________________), is uneven. This gives rise to 3 bond types.
• nonpolar covalent bonds: ____________ sharing of the e- pair
• polar covalent bonds: ________________ sharing of the e- pair
• ionic bonds: a ___________ of e-’s from the metal to the nonmetal
How To Determine the Bond Type
• Bond type is based on the electronegativity _____________ between the two bonded atoms.
electronegativity
equal
unequal
transfer
difference
Figure 12.4 The three possible
types of bonds.nonpolar
polar
ionic
Polarity of Molecules
• One side is slightly (__) and the other side is slightly (__).
• Polar molecules are also known as _______________.
• Polarity depends on the __________ and symmetry of the molecule.
• symmetrical molecules (looks the same on all sides)= ___________
• asymmetrical molecules = ___________
• Polar molecules are moved by ____________ charges.
+ –
dipole
shape
nonpolar
polar
static
Molecular Polarity
Practice Problems: Determine if the following molecules are polar or nonpolar based on their shape.
a) CH4 b) NH3 c) H2O d) HCl e) BF3
symmetrical tetrahedral
asymmetrical pyramid
asymmetrical bent
asymmetrical linear
symmetrical trigonal planar
nonpolar nonpolarpolar polar polar
Dipole of NH3
Dipole of H2O
Bond Dissociation Energy
• This is the energy needed to ___________ the bond.
• Generally, the longer the bond, the _____ energy it takes to break it.
• Single bonds take ________ energy to break than double bonds and triple bonds require the _________ energy to break.
• When bonds form, energy is _____________.
(Breaking bonds requires the addition of energy.)
released
less
lessmost
break
Bond Dissociation Energy
Intermolecular Attractions
• The __________ attractions between one molecule and another are called _______ ______ ________ forces.
• They cause gas particles to stick together and _______________ at low temperatures.
weak Van der Waals
condense
Dispersion Forces
There are two types of intermolecular forces:
(1) ____________________ forces: (the weaker type)
– caused by random _______________ motion
– generally _____________ with ________ electrons in the molecule
Dispersion
electronstronger more
− exist between all types of molecules
− This force causes Br2 to be a liquid and I2 to be a solid at room temperature.
Dipole Interaction Forces
(2) ____________ interactions: (the stronger force)
– caused by the attraction of the (__) side of one polar molecule and the (__) side of a different polar molecule
Dipole
+–
Hydrogen Bonds
•________________ “Bonds” are a special type of dipole interaction.
• This attraction between molecules is not a chemical bond. Electrons are not being shared or transferred.
•They occur between the hydrogen of one polar molecule and the ____, ___ or ___ of another polar molecule.
Hydrogen Bonding in Water
Hydrogen
N O F
Hydrogen Bonds
• The ladder rungs in a DNA molecule are hydrogen bonds between the base pairs, (AT and GC).
Intermolecular Forces At Work
•Substances that contain stong intermolecular forces have a ________ melting point and a _________ boiling point.
• Liqids containing strong intermolecular forces have higher surface tension and a higher viscosity.
higherhigher
Surface Tension
Properties of Ionic Compounds and Covalent Molecules
Molecular:
• ________________ of electricity
• formed between two _______________
• usually have ________ melting points
• solubility in water _______: (polar =dissolve; nonpolar = insoluble)
•forms ______________________solids.
Insulators
nonmetals
low
varies
covalent crystalline
Properties of Ionic Compounds and Covalent Molecules
Ionic:
•_______________ of electricity when dissolved water or melted.
•formed between __________ and _________________
•have _________ melting points
•usually ________ soluble in water
• form ___________________ solids
Conductors
metals nonmetals
high
very
ionic crystalline
(dissolved salt)