Chem Module 3 Exam

General concepts

• how covalent vs ionic bondings work

• the relationship between longer-weaker bonds

• bond dissociation energy

• pi vs sigma bonds

• energy in vs energy out in reactions

• MO theory

She brought us a true or false questions on these concepts so be sure to be prepared. 

Lewis dot structures

• count valence electrons, put the least electronegative atom in the center, connect it with others atoms with single bonds, attach none bonding electron pairs, count out the formal changes, create double bonds if formal charges don’t line up. 

Remember, if your compound is charged, put the negative formal charges on the most electronegative atom (usually oxygen) and do not forget your brackets!!! Also, you can only extend the octet for elements in the third row and below (never have carbon attached to 5 things for example). Be able to draw the molecules in 3D space (wedges and dashes).

Valence bond theory, geometries, drawing orbitals - she will ask about this, put the graph with all the parent geometries in your cheat sheet please!!! Also, extremely important, you should be able to draw orbital interactions that form covalent bonds: look at the guided inquiry from last week’s workshop for this. All the concepts about how the length of a covalent bond affects its strength apply.

4. Molecular orbitals - you will be tested on drawing homogeneous molecular orbitals: N2, H2, Cl2, etc. Remember, the number of orbitals going in = number of orbitals coming out. Be sure to know how to calculate bond order (put the formula on your cheat sheet). Matson will also ask about how bond order relates to bond strength and length - remember, increased bond order always means creating stronger bonds, and therefore shorter length. Decreasing bond order - weaker bonds, longer bond length.