VSEPR Theory: Molecular Shapes Most shapes are based on a __________________. Examples: CH 4 CCl 4 Removing the top of the tetrahedral makes the ________________.

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)