Chpater 4: Lewis structures, AXE, Molecular geometry, isomers, resonance structures, sigma + pi bonds Flashcards
What molecular shape is AX?
Linear
What molecular shape is AX2?
Linear
What molecular shape is AX3?
Trigonal planar
What molecular shape is AX4?
Tetrahedron
What molecular shape is AX5?
Trigonal bipyramid
What molecular shape is AX6?
Octahedron
What molecular shape is AX2E?
V- shape
What molecular shape is AX3E?
Trigonal pyramid
What molecular shape is AX2E2?
Bent V/ Compressed V
What molecular shape is AXE3?
Linear
What molecular shape is AX4E
SeeSaw
What molecular shape is AX3E2
T shaped
What molecular shape is AX2E3
Linear
What molecular shape is AX5E
Square pyramid
What molecular shape is AX4E2
Square planar
How do you write an AXE formula?
A represents the central atom
X represents the number of BONDS (or bonding pairs of electrons)
- X can only go up to 6
E represent the number of any non bonding (or “lone”) PAIRS of electrons located on the central atom
- E can only go up to 3
Example formula: AX3E
- one central atom
- 3 bonds on central atom (meaning central atom is bonded to 3 molecules)
- one lone PAIR of electrons (count the PAIR not how many electrons are unpaired, if there are 2 electrons that aren’t paired, that’s ONE lone pair)
What is a single bond?
A single bond is also a SIGMA bond
What is a double bond?
1 Sigma + 1 Pi bond
What is a triple bond?
1 Sigma + 2 Pi bonds
How to draw a lewis structure
Step 1. Count all valence electrons
Step 2. determine central atom (atom there is only one of, or atom farthest to the left)
Step 3. Draw single bonds to central atom
Step 4. Put alll remaining valence electrons on atoms as lone pairs
Step 5. Check if every atom has an octect (if i t follows octect rule). Turn lone pairs into double or triple bonds to fill octect rule (IF NEEDED)
How do you know if a structure has resonance?
When you have a double bond or lone pairs, and can arrange them in a different way. You can only rearrange the electrons in a resonance structure, the atoms MUST stay in the same position.
- look for double bonds or double bonds with lone pairs of electrons
How do you know when a structure has an isomer?
When you can rearrange the atoms and electrons in the structure. If you can only rearrange the electrons, that is a RESONANCE structure and NOT an isomer.
- look for multiple central atoms
When do you use a double or triple bond?
If we run out of valence electrons but the central atom still needs electrons to make an octet- transfer pairs of electrons from lone pairs on a satellite atom into a bond between the satellite atom and the central atom.
- This will make a double bond between the central atom and that satellite atom.
- You can do this again as needed to make an octet on the central atom. This will make a triple bond.
When does expanded valence start and what does it mean?
Expanded Valence compounds means they can have 10 or 12 electrons around them
- Expanded valence begins with the element Phosphorus and continues in the Periodic Table from this element on
- central atom can only have 12 electrons on it (meaning only 2 lone PAIRS or 4 electrons)
When does the ocelet rule start?
Ocelet rule begins after carbon
What is the ocelet rule?
the tendency of atoms to prefer to have eight electrons in the valence shell
Which atoms do NOT follow the ocelet rule?
Hydrogen (H), Lithium (Li), Berilliyum (Be), and Boron (B)
How do you find formal charge?
F.C: Valence electrons- nonbonded electrons - # of bonds
- a formal charge of 0 is ideal, -1 or +1 is fine, anything beyond -2 or +2 is unstable and cannot exist
- nonbonded electrons = each electron, NOT each pair
- ex: 1 pair = 2 electrons, so subtract 2 in equation
What is an isomer?
Isomers are two or more compounds with the exact same Formula but with a different arrangement of atoms (bonding pattern).
- 2 types: Structural isomerism, Geometric isomerism
- Structural” Isomerism” or “Constitutional Isomerism” = the atoms in each molecule have different structural connections
- “Geometric Isomerism” = the molecules are connected exactly the same way but are geometrically held into different positions by the presence of double bonds (or ring structures).
What is resonance?
electron movement relative to the nuclei, with the nuclei staying in place.
- The most common form of resonance is lone pair moving to create a double bond, or double bond moving to a lone pair.
- pay attention to formal charge, even though you can move stuff around, if the formal charge is too high it’s impossible
How to determine polarity?
The first factor is the presence of at least one highly electronegative atom bonded to an atom of far less electronegativity (Remember that F is most electronegative, then Cl and O, then Br, N, S, then C, H, etc)
The second factor is “unsymmetrical” geometry. If the geometry of the molecule is constructed such that the electronegativity “dipoles” pull in opposite directions (or symmetrically cancel each other) –these dipoles will cancel out and the molecule will not be polar despite the fact that it has a highly electronegative atom present.
