VSEPR Theory: Molecular Shapes Most shapes are based on a __________________. Examples: CH 4 CCl 4 Removing the top of the tetrahedral makes the ________________ shape. Examples: NH 3 PCl 3 tetrahedral pyramidal

VSEPR Theory: Molecular Shapes Removing one side of the pyramid makes the _____________ shape. Examples: H 2 O H 2 S If there are only two atoms bonded, it is ______________. Examples: O 2 HCl CO 2 (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: BF 3 (Notice that Boron will only have ___ e - ’s around it. The missing pair of electrons will make it planar instead of ________________.) 3 plane 6 pyramidal

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: PCl 5 and SF 6 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) CH 4 b) NH 3 c) H 2 O d) HCl e) BF 3 symmetrical tetrahedral asymmetrical pyramid asymmetrical bent asymmetrical linear symmetrical trigonal planar nonpolar polar Dipole of NH 3 Dipole of H 2 O

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 most 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 electron strongermore − exist between all types of molecules − This force causes Br 2 to be a liquid and I 2 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. higher

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 metalsnonmetals high very ionic crystalline (dissolved salt)