Electronegativity & Bonding — Structured Questions (Cambridge International A-Level Chemistry): Exam Questions

Define the term electronegativity.

A bond between nitrogen and hydrogen can be represented as $\overset{δ-}{N}\overset{δ+}{H}$.

i) In this representation, state the meaning of the symbol δ+.

ii) From this bond representation, state what can be deduced about the electronegativity of nitrogen relative to that of hydrogen.

State three factors which affect the electronegativity of an element.

Extract:

State three factors which affect the electronegativity of an element.

Three factors which affect the electronegativity of an element:

• Nuclear charge
• Atomic radius
• Shielding (by inner electrons)

i) Identify the element in Period 4 with the highest electronegativity value.

ii) Explain why fluorine is more electronegative than oxygen.

The electronegativities of some elements are shown in Table 3.1.

Table 3.1

Define the term electronegativity.

Extract:

The electronegativities of some elements are shown in Table 3.1.

Table 3.1

Use Table 3.1 to explain the trend in electronegativity across the Periodic Table.

Extract:

The electronegativities of some elements are shown in Table 3.1.

Table 3.1

Explain how the carbon-hydrogen bond (such as in CH₄) differs from the nitrogen-hydrogen bond (such as in NH₃) in terms of the bond polarity.

Extract:

The electronegativities of some elements are shown in Table 3.1.

Table 3.1

Explain, in terms of electronegativity, why the bonding in ammonia (NH₃) is covalent but the bonding in lithium chloride (LiCl) is ionic.

Chlorine (Cl) reacts with boron (B) to form boron trichloride (BCl₃).

i) What type of bond is the B-Cl bond?

ii) How is this bond formed?

iii) The electronegativities of boron, chlorine and hydrogen are 2.0, 3.2 and 2.2 respectively. Is the B-Cl more or less polar than a B-H bond in borane (BH₃)? Explain your answer.

Molecules and separate atoms (such as noble gases) are attracted to one another by intermolecular forces.

i) What is the strongest type of intermolecular force that takes place between water (H₂O) molecules?

ii) Draw a diagram that illustrates the interaction between two water molecules. Indicate any lone pairs of electrons and partial charges in your diagram.

The boiling point of tetrachloromethane (CCl₄) is 77 °C whereas the boiling point of water (H₂O) is 100 °C.

i) Suggest why the boiling point of H₂O is higher than that of CCl₄.

ii) Predict whether the boiling point of methane (CH₄) is higher or lower than the boiling point of CCl₄. Explain your answer.

Define the term electronegativity.

State and explain the general trend in electronegativity across a period.

Chlorine, Cl₂, reacts with boron, B, to form boron trichloride, BCl₃.

i) What type of bond is the B-Cl bond?

ii) How is this bond formed?

iii) The electronegativities of boron, chlorine and hydrogen are 2.0, 3.2 and 2.2 respectively. Is the B-Cl more or less polar than a B-H bond in borane, BH₃? Explain your answer.

The Pauling electronegativity values of different elements are shown in Fig. 3.1.

Fig. 3.1

A compound formed from magnesium and oxygen has a different structure to a compound formed from phosphorus and oxygen.

Predict the type of bonds that will occur in each compound. Explain your answer.

Explain why the melting point of phosphorus(III) oxide, P₄O₆, is lower than that of magnesium oxide in terms of their bonding and structure.

Phosphorus(III) oxide, P₄O₆, contains no P–P or O–O bonds.

In the P₄O₆ molecule, all oxygen atoms are bonded to two other atoms and all phosphorus atoms are bonded to three other atoms.

Sketch a structure for P₄O₆.

Extract:

The Pauling electronegativity values of different elements are shown in Fig. 3.1.

Fig. 3.1

Explain the difference in electronegativity shown in Fig. 3.1 between magnesium and calcium.