Chapter 3.3

Question 1

What is bond energy? How does it relate to the number of electrons

Answer 1

• it is the energy required to break a bond
• > by separating components into their isolated gaseous atomic states

-greater number electrons shared between atoms= greater bond energy

Question 2

Distinguish between a lewis acid and a lewis base. Give an example

Answer 2

• lewis base is one that will donate a lone pair of electrons
• lewis acid is one that accepts a lone pair of electrons

-eg; NH3(lewis base) + BF3(lewis acid)

Question 3

How do you choose from different Lewis structures that have the same connectivity but differ in the arrangement of electron pairs

Answer 3

• look at their formal charge

- the one with the lowest number and magnitude of formal charge is usually the most stable arrangement of the compound

Question 4

What are resonance structures?

Answer 4

• same arrangement of atoms

- >but differ in the placement of electrons

Question 5

How to use formal charge to assess the stability of a resonance structure? Three methods

Answer 5

1) A lewis structure with small or no formal charges is preferred over a Lewis structure with large formal charges
2) A Lewis structure with less separation between opposite charges is preferred over a Lewis structure with a large separation of opposite charges
3) Lewis structure in which formal charges are placed on more electronegative atoms is more stable

Question 6

What is the difference between electronic geometry and molecular geometry

Answer 6

Electronic

• > describe the spatial arrangement of all pairs of electrons around the central atom
• > including both the bonding and lone pairs

Molecular
->describes the spatial arrangement of only the bonding pairs of electrons

Question 7

What is coordination number

Answer 7

-it is the number of atoms that surround and are bonded to a central atom

Question 8

How do lone pairs influence molecular geometry

Answer 8

• it decreases the bond angle
• non-bonding pairs exert more repulsion than bonding pairs
• > because these electrons reside closer to the nucleus

Question 9

What happens when two orbitals come together? Describe the signs of orbitals and what kind of orbital it forms.

Answer 9

• when two atomic orbitals come together
• > they form a molecular orbital
• if signs of two orbitals are the same
• > a bonding orbital forms
• if the signs of two orbitals are different
• > then an antibonding orbital forms

Question 10

Describe the difference between sigma bonds and pi bonds

Answer 10

Sigma bonds

• > allows for free rotation around the axes
• > electron density is a single linear accumulation between atomic nuclei

Pi bonds

• > orbitals overlaop
• > there are two parallel electron cloud densities
• > so a pi bond is formed
• > no free rotation
• > because electron densities are parallel and cannot be twisted in such a way