IB DP Chemistry Topic 4.2 Covalent bonding SL Paper 1

Question

Which statement best describes the intramolecular bonding in HCN(l)?

A.     Electrostatic attractions between \({{\text{H}}^ + }\) and \({\text{C}}{{\text{N}}^ – }\) ions

B.     Only van der Waals’ forces

C.     Van der Waals’ forces and hydrogen bonding

D.     Electrostatic attractions between pairs of electrons and positively charged nuclei

▶️Answer/Explanation

D

HCN has Electrostatic attractions between pairs of electrons of \({\text{C}}{{\text{N}}^ – }\) ion and positively charged nuclei of \({{\text{H}}^ + }\) . 

Question

Which molecule has the shortest bond between carbon atoms?

A.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}\)

B.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\)

C.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}\)

D.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{C}}{{\text{l}}_{\text{2}}}\)

▶️Answer/Explanation

C

HC≡CH , C -C Bond order =3 

H2C=CH2 , C-C Bond order =2

H3C-CH3 , C-C Bond order =1 

ClH2C-CH2Cl , C-C Bond order =1 

More the bond order, lesser will be the bond length.

Hence, \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}\) has the shortest bond between carbon atoms. 

Question

When \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}\), \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\) and \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}\) are arranged in order of increasing carbon-carbon bond strength (weakest bond first), what is the correct order?

A.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}\)

B.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\)

C.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}\)

D.     \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}\)

▶️Answer/Explanation

C

HC≡CH , C -C Bond order =3 

H2C=CH2 , C-C Bond order =2

H3C-CH3 , C-C Bond order =1 

Higher the bond order, lower is the bond length and higher is the bond strength. 

So, the increasing order of carbon-carbon bond strength is : 

\({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{\text{, }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{2}}}\)

Question

The number of electrons in the valence shell of elements A and B, are 6 and 7 respectively. What is the formula and type of bonding in a compound formed by these elements?

A.     \({{\text{A}}_{\text{2}}}{\text{B}}\), covalent

B.     \({\text{A}}{{\text{B}}_{\text{2}}}\), covalent

C.     \({{\text{A}}_{\text{2}}}{\text{B}}\), ionic

D.     \({\text{A}}{{\text{B}}_{\text{2}}}\), ionic

▶️Answer/Explanation

B

Each atom requires 8 electrons to complete its shell. Here, A is short of two electrons and B is short of 1 electron to complete its shell. 

Two B atoms share its electrons with A forming two A-B covalent bonds. 

Compound formed will be \({\text{A}}{{\text{B}}_{\text{2}}}\) and covalent. 

Question

Which bonds are arranged in order of increasing polarity?

A.     H–F \( < \) H–Cl \( < \) H–Br \( < \) H–I

B.     H–I \( < \) H–Br \( < \) H–F \( < \) H–Cl

C.     H–I \( < \) H–Br \( < \) H–Cl \( < \) H–F

D.     H–Br \( < \) H–I \( < \) H–Cl \( < \) H–F

▶️Answer/Explanation

C

Order of the polarity of the molecules depends on the electronegativity of the bonded atoms. The E.N order for halogens is given below.

F>Cl>BrI

Therefore, the order of polarity of hydrogen halide molecules is

H-I<H-Br<H-Cl<H-F.

Question

Which single covalent bond is the most polar, given the following electronegativity values?

A.     C–O

B.     S–H

C.     C–H

D.     O–H

▶️Answer/Explanation

D

Polarity is determined by difference of electronegativity values of atoms. 

E.N. difference : C-O = 3.4-2.6 = 0.8

E.N. difference : S-H = 2.6-2.2 = 0.4

E.N. difference : C-H = 2.6-2.2 = 0.4

E.N. difference : O-H = 3.4-2.2 = 1.2

Hence, O-H has maximum difference of electronegativity, it is most polar. 

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