Chpater 4: Lewis structures, AXE, Molecular geometry, isomers, resonance structures, sigma + pi bonds

Question 1

What molecular shape is AX?

Answer 1

Linear

Question 2

What molecular shape is AX2?

Answer 2

Linear

Question 3

What molecular shape is AX3?

Answer 3

Trigonal planar

Question 4

What molecular shape is AX4?

Answer 4

Tetrahedron

Question 5

What molecular shape is AX5?

Answer 5

Trigonal bipyramid

Question 6

What molecular shape is AX6?

Answer 6

Octahedron

Question 7

What molecular shape is AX2E?

Answer 7

V- shape

Question 8

What molecular shape is AX3E?

Answer 8

Trigonal pyramid

Question 9

What molecular shape is AX2E2?

Answer 9

Bent V/ Compressed V

Question 10

What molecular shape is AXE3?

Answer 10

Linear

Question 11

What molecular shape is AX4E

Answer 11

SeeSaw

Question 12

What molecular shape is AX3E2

Answer 12

T shaped

Question 13

What molecular shape is AX2E3

Answer 13

Linear

Question 14

What molecular shape is AX5E

Answer 14

Square pyramid

Question 15

What molecular shape is AX4E2

Answer 15

Square planar

Question 16

How do you write an AXE formula?

Answer 16

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)

Question 17

What is a single bond?

Answer 17

A single bond is also a SIGMA bond

Question 18

What is a double bond?

Answer 18

1 Sigma + 1 Pi bond

Question 19

What is a triple bond?

Answer 19

1 Sigma + 2 Pi bonds

Question 20

How to draw a lewis structure

Answer 20

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)

Question 21

How do you know if a structure has resonance?

Answer 21

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

Question 22

How do you know when a structure has an isomer?

Answer 22

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

Question 23

When do you use a double or triple bond?

Answer 23

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.

Question 24

When does expanded valence start and what does it mean?

Answer 24

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)

Question 25

When does the ocelet rule start?

Answer 25

Ocelet rule begins after carbon

Question 26

What is the ocelet rule?

Answer 26

the tendency of atoms to prefer to have eight electrons in the valence shell

Question 27

Which atoms do NOT follow the ocelet rule?

Answer 27

Hydrogen (H), Lithium (Li), Berilliyum (Be), and Boron (B)

Question 28

How do you find formal charge?

Answer 28

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

Question 29

What is an isomer?

Answer 29

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).

Question 30

What is resonance?

Answer 30

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

Question 31

How to determine polarity?

Answer 31

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.