Question 1a

Marks: 4

a)

Deduce the number of possible resonance structures for the carbonate ion, CO₃^2-, and draw two of them.

Include the formal charges for each oxygen.

[4]

Key Concepts

Resonance structures
Formal Charge

Question 1b

Marks: 2

b)

An alternative structure for the carbonate ion is proposed:

ib-hl-sq-14-1-h-proposed-incorrect-carbonate-structure-q1b

Explain why this structure is not accepted as another resonance structure for the carbonate ion.

[2]

Key Concepts

Applying Formal Charge

Question 1c

Marks: 2

c)

Deduce the number of sigma (σ) and pi (π) bonds present in any of the resonance structures of the carbonate ions shown in part a).

[2]

Key Concepts

Sigma Bonds
Pi Bonds
Predicting the Type of Bonds

Question 1d

Marks: 1

d)

Deduce the bond order of the C-O bond in the carbonate ion, CO₃^2-.

[1]

Question 2a

Marks: 6

a)

Silicon can form silicon tetrachloride SiCl₄ and also silicon hexachloride, SiCl₆^2-.

i)

Draw the Lewis structure for SiCl₄ and SiCl₆^2-.

[2]

ii)

Use VSEPR theory to deduce the Cl-Si-Cl bond angles in both the SiCl₄ and SiCl₆^2- molecules.

[2]

iii)

Predict the molecular geometry of each molecule.

[2]

Key Concepts

More Lewis Structures
Further VSEPR Theory

Question 2b

Marks: 3

b)

Carbon can form CCl₄but cannot form CCl₆^2-. Explain why.

[3]

Key Concepts

Octet Rule Exceptions

Question 2c

Marks: 2

c)

Deduce which, if any, of SiCl₄ and SiCl₆^2-, are polar molecules and explain your choice.

[2]

Key Concepts

Further VSEPR Theory

Question 2d

Marks: 6

d)

Formal charge can be used to decide on the most stable, and therefore most likely, form a molecule can take. Resonance structures occur when more than one Lewis diagram describes a structure equally well.

i)

Deduce the formal charge on the silicon and each chlorine within SiCl₄ and SiCl₆^2-

[2]

ii)

Predict which will be the most stable molecule and explain your answer.

[2]

iii)

Predict if any resonance structures are possible for SiCl₆^2- and explain your answer.

[2]

Key Concepts

Formal Charge
Applying Formal Charge
Delocalisation & Resonance

Question 3a

Marks: 4

a)

Natural rubber, polyisoprene, forms a flexible polymer in the following reaction:

ib-hl-sq-14-1-h-structures-of-isopropene-and-polyisopropene-q3a

i)

Deduce the number of sigma (σ) and pi (π) bonds in the monomer.

[2]

ii)

Deduce the number of sigma (σ) and pi (π) bonds in the repeating unit.

[2]

Key Concepts

Predicting the Type of Bonds

Question 3b

Marks: 2

b)

Deduce the number of carbons with a tetrahedral geometry in both the monomer, isoprene, and the repeating unit of the polymer, polyisoprene.

[2]

Key Concepts

Predicting Shapes & Bond Angles

Question 3c

Marks: 4

c)

Polymer formation involves a radical intermediate to lengthen the polymer chain.

The radical in the formation of polyisoprene is shown below, where X represents the existing chain:

X-CH₂CCH₃CHCH₂

i)

Identify the atom that is the radical in the structure shown.

[1]

ii)

Deduce the formal charge on the radical atom.

[1]

iii)

Use the information above, and your knowledge of structure and bonding, to predict if the structure is stable or not.

[2]

Key Concepts

Formal Charge
Applying Formal Charge

Question 3d

Marks: 2

d)

Isoprene is not produced directly by the rubber tree, but is the product of a series of biochemical reactions from the isopentenyl pyrophosphate molecules present in the tree.

The structure of isopentenyl pyrophosphate is shown below:

ib-hl-sq-14-1-h-structure-of-isopentenyl-pyrophosphate-q3d

`Deduce the number of sigma (σ) and pi(π) bonds present in one molecule of isopentenyl pyrophosphate.

[2]

Key Concepts

Predicting the Type of Bonds

Question 4a

Marks: 4

a)

One interhalogen compound is IF₅.

i)

Draw the Lewis structure for IF₅.

[1]

ii)

Use VSEPR theory to deduce the bond angles in IF₅.

[1]

iii)

Predict whether IF₅ will be a polar molecule and explain your choice.

[2]

Key Concepts

More Lewis Structures
Octet Rule Exceptions

Question 4b

Marks: 4

b)

Iodine can also form the triiodide ion, I₃^-.

i)

Draw the Lewis structure for I₃^-.

[1]

ii)

Use VSEPR theory to deduce the bond angles in I₃^-.

[1]

iii)

Explain the position of the lone pairs on the central iodine.

[2]

Key Concepts

More Lewis Structures
Further VSEPR Theory

Question 4c

Marks: 2

c)

Deduce the formal charge on each of the iodine atoms in the triiodide molecule, I₃^-.

[2]

Key Concepts

Formal Charge

Question 4d

Marks: 3

d)

An alternative Lewis structure for the triiodide ion, I₃^-, is suggested:

ib-hl-sq-14-1-h-alternative-lewis-structure-for-the-triiodide-ion-q4d

Deduce the formal charges and use them to suggest if the structure is stable and likely to occur.

[3]

Key Concepts

Applying Formal Charge

DP IB Chemistry: HL

Topic Questions

14.1 More Structures & Shapes

Question 1a

Key Concepts

Question 1b

Key Concepts

Question 1c

Key Concepts

Question 1d

Question 2a

Key Concepts

Question 2b

Key Concepts

Question 2c

Key Concepts

Question 2d

Key Concepts

Question 3a

Key Concepts

Question 3b

Key Concepts

Question 3c

Key Concepts

Question 3d

Key Concepts

Question 4a

Key Concepts

Question 4b

Key Concepts

Question 4c

Key Concepts

Question 4d

Key Concepts

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