Week 5 - Shapes of Molecules

Question 1

Formal charge of an atom

Answer 1

the hypothetical charge the atom would have if we could redistribute the electrons in the bonds evenly between atoms

Question 2

Formula for determining formal charge, how to determine each variable

Answer 2

FC = valence electrons - lone pair electrons - (1/2) bonding electrons

• valence refers to its spot on the periodic table from 1-8
• lone pair electrons refers to the number of electrons not bonded
• bonding electrons is the number of electrons in bonds with other atoms

Question 3

When a molecule has multiple possible structure orientations, it is called…

Answer 3

resonance structure

Question 4

When examining resonance structures, what is preferred?

Answer 4

Formal charge of 0 is best, smallest formal charge possible, and a negative formal charge; if formal charges are the same the one with a preferable value on a more electronegative element is preferred

Question 5

Resonance structures only exist…

Answer 5

on paper

Question 6

Why should we care about molecular geometry?

Answer 6

• molecular polarity
• physical properties, intermolecular forces
• binding
• reactivity

Question 7

What does VSEPR stand for, and what is it?

Answer 7

valence shell electron pair repulsion theory; the idea of maximizing space between valence electron groups around an atom

Question 8

What angles can 3-element groups be?

Answer 8

120 ̊, <120 ̊ (lone pair)

Question 9

What angles can 2-element groups be?

Answer 9

180 ̊

Question 10

What angles can 4-element groups be?

Answer 10

109.5 ̊, <109.5 ̊ (lone pair)

Question 11

What angles can 5-element groups be?

Answer 11

120 ̊, 90 ̊, <120 ̊ (lp), <90 ̊ (lp), 180 ̊

Question 12

What angles can 6-element groups be?

Answer 12

90 ̊, <90 ̊ (lp)