University:
Seattle Pacific University
Course:
CHM 1211 | General Chemistry I
Academic year:

2020
Views:

11

Pages:

3
Author:

Accinkiquicpqw

Chem Notes Exceptions to Octet Rule *Bond – Link between two atoms; molecule can have many bonds *Chapter 9 contains no math *You may bring aluminum foil to the final to form molecular shapes *When doing x-ray crystallography, we only see atoms of molecule – we do not see electrons Molecular Geometries Observed – MUST KNOW THESE SHAPES *When looking at molecular geometry, pretend that lone pairs of e- are not there *Tetrahedral – 5 atoms *Octahedral – 8 faces *Bent – Any shape that is not linear (e.g., shape of water molecule is bent, meaning the H-O-H bond is not 180 degrees) Examples of more than an octet on the central atom *Put least electronegative in center *Put bonds around it *Add atoms of most electronegative *Put valence electrons *Only place for extra e- is on center atom *Six pair electrons (12 e-) is the max # e- on one atom *Expanded octet – Any molecule that has more than an octet of e- on the central atom Examples of more than one octet on the central atom Electron domain geometry – Places where e- are Molecular shape – physical shape of the molecule SF6 Molecular shape = octahedral – only shape with 6 bonds Electron domain geometry = octahedral ClF3 Molecular shape = t-shaped Electron domain geometry = trigonal bi-pyramid How Lewis Structure Theory Predicts Molecular Shapes I3¯ ion Molecular shape = Linear *I3¯ is more stable as a linear shape because the lone pairs of e- repel each other so they want to be as far apart as possible Practice a. CCl4 Electron domain geometry – tetrahedral Molecular geometry - tetrahedral b. SF4 Electron domain geometry – trigonal bi-pyramid Molecular geometry – see-saw c. Cl3¯ Electron domain geometry – trigonal bi-pyramid Molecular geometry – linear (more stable) d. XeF4 Electron domain geometry – octahedral Molecular geometry – square planar VSEPR *Non-bonding electron pairs repel each other the most (strongest repel) *Lone pair repels bonded pair (medium repel) *Bonded electrons repel each other the lease (weakest repel) VSEPR *H-O-H bond angle of water is smaller than H-N-H bond angle of NH3 because water has fewer electrons (fewer negative charges as lone pairs of e¯ = less repelled) How do bond polarities sum to determine molecular polarity? *Things alike will dissolve in each other (polar molecules will dissolve in other polar molecules) Some molecules that contain polar bonds, but not all of the molecules are polar *If forces cancel = non-polar *If forces don’t cancel = polar *If the molecule is polar it will be pulled in one direction O=C=O Non-polar C will not move because forces cancel out (C feels equal force from both O atoms) CCl4 Non-polar Forces cancel because bond angles are equal CH3Cl Polar Forces are not equal – C will move Why it costs a little energy to form hybrid orbitals *When orbitals overlap – energy created *To obtain this state – must put energy in *When put energy in – will get more energy out (good investment)