BPGHS SJChO Chemical Bonding IV

Multiple Choice

1. (Lv. 1) Which of the following is the correct electron-pair geometry for the simple covalent molecule OF₂?

• Linear

• Bent

• Tetrahedral

• Octahedral

Answer/Feedback

Drawing the structure of OF₂, there are a total of 4 electron domains surrounding O (2 bond pairs and 2 lone pairs).

Multiple Choice

2. (Lv. 1) Which of the following is the correct molecular geometry for the simple covalent molecule BrF₄⁺?

• Square planar

• See-Saw

• Trigonal bipyramidal

• Tetrahedral

Answer/Feedback

For the central Br atom, the covalent structure will have a total of 5 electron domains (1 electron has been lost to give it the + charge, 4 are bonded to F, remaining 2). From electron-pair geometry (trigonal bipyramidal) >> 1 lone pair >> therefore see-saw.

Multiple Choice

3. (Lv. 1) In which one of the following pairs do the molecules have similar shapes?

• AlCl₃ and BCl₃

• AlCl₃ and PCl₃

• BF₃ and NH₃

• CO₂ and SO₂

Answer/Feedback

AlCl₃ and BCl₃ = Trigonal planar.

PCl₃ and NH₃ = Trigonal Pyramidal.

CO₂ = Linear

SO₂ = Bent

Multiple Choice

4. (Lv. 1) Which of the following pairs contain 2 species with different shapes?

• NCl₃ and BrCl₃

• CO₃^2- and BBr₃

• BeCl₂ and BrCl₂^-

• SiF₄ and PF₄⁺

Answer/Feedback

NCl₃ = Trigonal pyramidal, BrCl₃ = T-shaped.

Multiple Choice

5. (Lv. 2) Which of the following species contain the smallest bond angle?

• N₂H₄

• BrF₅

• XeF₂

• SO₂

Answer/Feedback

N₂H₄ = 107.5^o

BrF₅ = ~109^o

XeF₂ = ~180^o

SO₂ = 120^o

Multiple Choice

6. (Lv. 2) Which of the following has the largest bond angle?

• PH₃

• SiCl₄

• IF₂^-

• IF₄^-

Answer/Feedback

PH₃ = ~107.5^o

SiCl₄ = ~109.5^o

IF₂^- = ~180^o

IF₄^- = 90^o

Multiple Choice

7. (Lv. 2) Adrenaline is a hormone which, when secreted directly into the bloodstream, acts as a stimulant. A derivative has the structure shown on the left. What are the values of angles E and F in that molecule shown on the left?

• E = 120^o, F=107^o

• E = 120^o, F=90^o

• E = 109^o, F=107^o

• E = 109^o, F=90^o

Answer/Feedback

Around angle E, the C is trigonal planar, which means the angle around is 120^o. For angle F, note that there are 4 electron domains (a lone pair is not shown). Since 1 of it is a bond pair, the shape around the N is trigonal pyramidal, therefore, the angle around N is 107^o.

Multiple Choice

8. (Lv. 2) The characteristic smell of garlic is due to alliin. When garlic is cut, an enzyme releases alliin because alliin has the right shape to fit the enzyme molecule. What will you expect the bond angles x, y and z to be, to the nearest 10^o in the molecule of alliin (shown on the left).

• x=120^o, y=110^o, z=110^o

• x=120^o, y=120^o, z=110^o

• x=180^o, y=90^o, z=90^o

• x=180^o, y=110^o, z=110^o

Answer/Feedback

Around angle x, the C is trigonal planar.

Around angle y, the S is tetrahedral.

Around angle z, the C is also tetrahedral.

Multiple Choice

9. (Lv. 2) In which set of species is the bond angle of the 2^nd species larger than the 1^st one?

• NCl₃ vs. H₂O

• BF₄^- vs. SCl₂

• PCl₆^- vs. ClO₂^-

• Br₂O vs. SF₆

Answer/Feedback

PCl₆^- = Octahedral, all bond angles are 90^o

ClO₂^- = Bent, bond angle at 104^o.

Multiple Choice

10. (Lv. 2) In which of the following reactions is the bond angle in the product greater than that of the reactant?

I. H₂O(l) + H⁺(aq) --> H₃O⁺(aq)

II. C₂H₄(g) + H₂(g) --> C₂H₆(g)

III. CO₂(g) + OH^-(aq) --> HCO₃^-(aq)

• I, II and III

• I and II

• II and III

• I only

Answer/Feedback

H₃O⁺ = tetrahedral, bond angle ~109.5^o, H₂O = bent, bond angle ~104^o.

Multiple Choice

11. (Lv. 2) For which of the following pairs does the 1^st species have a smaller bond angle?

I. XeF₄ vs. SeF₂

II. CrO₄^2- vs. SO₃^2-

III. BH₃ vs. AsH₃

• I, II and III are correct.

• I and II only are correct.

• II and III only are correct.

• I only is correct.

Answer/Feedback

XeF₄ = square planar, angle = 90^o, while SeF₂ = bent, angle = 104^o.

Multiple Select

12. (Lv. 3) Plants appear green due to the presence of chlorophyll. There are several closely related chlorophylls and the diagram on the left shows a simplified version of 1. The various different side groups are all shown as R. Which of the following statements are correct?

• N¹ and N³ engages in dative covalent bonding to Mg.

• The molecular geometry about Mg is planar.

• Mg has a charge of +2.

• N² and N⁴ has a lone pair of electron not used for bonding.

Answer/Feedback

N¹ and N³ engages in simple covalent bonding with the central Mg. Since Mg forms 2 simple bonds, it's charge is +2. N² and N⁴ uses its lone pair of electrons remaining to form a dative covalent bond with Mg - these do not cause Mg to obtain a charge (note that the formula for formal charges can also be used to calculate Mg's charge). Due to the entire flat structure + the configurations and bonding of the Ns to Mg, it forces Mg to adopt a flat structure.

Multiple Choice

13. (Lv. 1) What value of the bond angles in an AsH3 molecule would the V.S.E.P.R. Theory predict?

• > bond angle of NH₃ but < bond angle of PH₃.

• <Bond angle of NH₃ but > bond angle of PH₃.

• < the bond angles of both NH₃ and PH₃

• > the bond angles of both NH₃ and PH₃.

Answer/Feedback

As is 1 period below P, and in the same Group with N and P. As such, it will be less electronegative than P and N. As such, the bonding electrons will be even closer to the H than that compared to PH₃ and NH₃ resulting in an even smaller bond angle.

Multiple Choice

14. (Lv. 1) which of the following molecules are not polar?

I. C₂H₆

II. TeF₄

III. AsF₃

• I II and III are correct.

• I and II are correct,

• II and III are correct

• I only is correct.

Answer/Feedback

Recall that whether a molecule is polar or not, has to consider the molecular geometry. For C and H, the electronegativity difference is very very minimal, so much so that the C-H is considered non-polar.

Multiple Choice

15. (Lv. 2) Which of the following molecules has the largest dipole?

Answer/Feedback

Note that a Cl atom is more electronegative than a -CH₃ component. This will therefore assist to cancel out a bit of the electronegativity difference and thus nullify the uneven charge distribution. For option D, the dipole cancel out (whether you consider top vs. bottom or left vs. right).

Multiple Choice

16. (Lv. 2) Which of the following pairs consist of a planar molecule and a polar molecule?

• CH₂=CH₂ and PCl₃

• CH₂=CH₂ and CCl₄

• CH₃COCH₃ and PCl₃

• CH₃COCH₃ and CCl₄

Answer/Feedback

The CH₂=CH₂ molecule is completely flat as each C is a trigonal planar configuration. PCl₃ is trigonal pyramidal in shape, with an uneven distribution of electrons between P and Cl due to electronegativity differences.

Multiple Choice

17. (Lv. 2) Carbon forms double bonds with each of the Group VI elements oxygen, sulfur and selenium. In each case, the double bond is polar. In the molecules carbon dioxide, carbonyl sulfide and carbonyl selenide, the polarities of these double bonds do not necessarily cancel, as shown by the table on the left. Which factors could account for these observations?

I. The C=S bond is more polar than the C=Se bond.

II. The C=O bond is more polar than the C=S bond.

III. The C=Se bond is more polar than the C=O bond.

• I, II and III only.

• I and II only.

• II and III only.

• I only.

Answer/Feedback

The CH₂=CH₂ molecule is completely flat as each C is a trigonal planar configuration. PCl₃ is trigonal pyramidal in shape, with an uneven distribution of electrons between P and Cl due to electronegativity differences.

Multiple Choice

18. (Lv. 1) The gecko, a small lizard can climb up a smooth glass window. The gecko has millions of microscopic hairs on its toes and each hair has thousands of pads at its tip. The result is that the molecules in the pads are extremely close to the glass surface on which the gecko is climbing. What is the attraction between the gecko's toe pads and the glass surface?

• Dative covalent bonds.

• Covalent bonds.

• Ionic Bonds.

• Van der Waals' forces.

Answer/Feedback

Since the gecko can easily climb, the attractive forces must form and dislodge easily. Thus, interatomic bonds are out of the question.

Multiple Choice

19. (Lv. 1) On the left shows a diagram depicting hydrogen bonding. Which of the following statements is correct about hydrogen bonding?

• It is stronger than ionic bonding.

• It is intramolecular.

• It allows molecules to bond covalently with each other.

• It increases a molecule's solubility in water.

Answer/Feedback

The ability of NH₃ to form a bonding with water will mean that it can be solvated by water molecules, supporting dissolution.

Multiple Choice

20. (Lv. 2) When water is stirred with glucose, strong hydrogen bonds are initially formed between glucose molecules and water molecules but, as more water as added, these hydrogen bonds are broken. If the process of bond breaking liberates heat, while bond forming absorbs heat, which of the following graphs best represent the observed temperature changes?

Answer/Feedback

Since bonds are initially formed, the liberated heat will cause an increase in temperature of the solution. However, as the bonds are broken and heat is taken in, the temperature subsequently decreases.

Multiple Choice

21. (Lv. 2) Which of the following show an increasing trend in boiling point?

I. Na, Mg, Al

II. PH₃, AsH_3, NH₃

III. BF₃, BCl₃, AlF₃

• I II and III

• I and II

• II and III

• I only

Answer/Feedback

I. Recall that the larger the charges in the metallic lattice + more valence electrons constitute stronger metallic bonding.

II. Although AsH₃ uses id-id interactions, its substantially larger size compared to PH₃ means that the former overcomes the pd-pd interactions of PH₃.

III. Extent of pd-pd interactions increases from left to right due to the increased electronegativity differences.

Multiple Choice

22. (Lv. 2) In which of the following pairs does the 1^st substance have a higher melting point than the 2^nd?

• CH₃CH₂OCH₃ vs. CH₃CH₂NHCH₃

• (CH₃)₃CH vs. CH₃CH₂CH₂CH₃

• RbCl vs. KCl

Answer/Feedback

The 1st compound takes part in intermolecular hydrogen bonding, while the other takes part in intramolecular hydrogen bonding.