Formal charges are a way of __. They may or may not what?
- keeping track of electrons
- correspond to actual charges in the molecule
Formula for formal charge. (2 methods)
- [group #] - [nonbonding electrons]- (1/2)[shared electrons]
- [group #] - [nonbonding electrons]-[number of bonds]
What would be an example of an atom with a formal charge. Explain why.
If Boron were to form four bonds, it would have a negative formal charge because it only contributes three. Therefore, it has one extra, making it negative.
Define Lewis acids and bases.
- bases donate pairs of electrons to form new bonds
- acids accept pairs of electrons to form new bonds
Shape of carbon with no octet? With octet?
- with no: plane
- with: tetrahedron with lone pair (trigonal pyramid)
What are the three geographies?
linear, trigonal planar, tetrahedral
Explain electronegativity trends.
increase from left to right and bottom to top
What is electonegativity?
ability to attract electrons in a covalent bond
What is a dipole moment?
amount of charge separation (δ) multiplied by bond length (μ )
Charge separation is shown by an __, where red indicates __ and blue indicates __.
- electrostatic potential map
- partially negative region
- partially positive region
Dipole moment is the __.
sum of the bond moments
True or False:
There is nothing more negative than a pair of lone electrons.
Dipole moments have two things. What?
direction and a magnitude
Dipole moments in nonpolar compounds __.
Explain resonance and its rules.
- both resonance structures contribute to the actual structure
- 1) cannot break single (sigma) bonds
- 2) only electrons move, not atoms
Three possibilities of resonance movement?
- - lone pair of electrons to adjacent bond position (forms pi bond)
- - pi bond to adjacent atom
- - pi bond to adjacent bond position
__ shows the flow of electrons.
What do arrows depict?
- curved arrow formalism
- electron pairs moving
The structures of some compounds are not adequately represented by a single Lewis structure. As a result, __, which are __.
The true structure will be __
- resonance forms are used
- Lewis structures that can be interconverted by moving electrons only
- a hybrid between the contributing resonance forms
How can resonance forms be compared?
- 1) has as many octets as possible
- 2) has as many bonds as possible
- 3) has the negative charge on the most electronegative atom
- 4) has as little charge separation as possible
When drawing Lewis structures in rings, what is a carbon bearing the appropriate number of hydrogens?
the intersection of any number of lines
When drawing Lewis structures, typically, what would you do?
bond the carbons to each other
When attached to two things only, what is the geometry?
What do curved arrows in a drawing signify?
to draw another structure
True or False:
Resonance structures oscillate between their multiple forms.
True or False:
Resonance is equilibrium.
Double bonds are __ and __.
In resonance, you do NOT __ or __. You only __.
- move atoms or break single bonds
- break double bonds
Knowing shapes and geometries tells us that they __.
rarely occur in nonpolar covalent bonds