Chemistry 9th Chap 5 : Topic 8 - Maryam Publications

Chemistry Chapter 5 : Topic 8

Forces and Melting Points

1 / 30

Why do ionic compounds generally have high melting points?

A) Their ions move freely in the solid state.

B) Their atoms contain a large number of neutrons.

C) Strong electrostatic forces act between oppositely charged ions.

D) Their ions are joined by weak intermolecular forces.

2 / 30

A covalent molecular compound melts at a low temperature mainly because:

A) its covalent bonds break easily

B) its atoms are arranged in an ionic lattice

C) weak forces exist between its molecules

D) its molecules contain no electrons

3 / 30

Which substance is expected to have the highest melting point?

A) Sodium chloride, NaCl

B) Chlorine, Cl₂

C) Methane, CH₄

D) Carbon dioxide, CO₂

4 / 30

When sodium chloride melts, which forces are mainly overcome?

A) Electrostatic attractions between Na⁺ and Cl⁻ ions

B) Nuclear forces inside the ions

C) Covalent bonds between sodium and chlorine atoms

D) Metallic bonds between sodium ions

5 / 30

Which statement correctly explains the low boiling point of methane?

A) Methane contains weak forces between its molecules

B) Methane molecules have strong ionic attractions

C) Carbon–hydrogen covalent bonds break during boiling

D) Methane has a giant covalent structure

6 / 30

Which change usually increases the melting point of an ionic compound?

A) Increasing the charges on its ions

B) Decreasing the charges on its ions

C) Increasing the distance between its ions

D) Converting its ions into neutral molecules

7 / 30

Magnesium oxide has a higher melting point than sodium chloride mainly because:

A) NaCl contains stronger covalent bonds.

B) MgO has weaker electrostatic attractions.

C) Mg²⁺ and O²⁻ have greater ionic charges.

D) MgO contains molecules larger than NaCl molecules.

8 / 30

Which pair of ions is expected to experience the strongest electrostatic attraction?

A) K⁺ and Br⁻

B) Li⁺ and F⁻

C) Mg²⁺ and O²⁻

D) Na⁺ and Cl⁻

9 / 30

If two ionic compounds contain ions with the same charges, the compound with smaller ions usually has:

A) weaker attraction and a lower melting point

B) weaker attraction and a higher boiling point

C) stronger attraction and a higher melting point

D) no attraction between its ions

10 / 30

Which ionic compound is likely to have the stronger attraction between its ions?

A) Attraction cannot depend on ionic size

B) KBr

C) Both have exactly the same attraction

D) LiF

11 / 30

During the boiling of water, which force is mainly overcome?

A) The bonds inside oxygen nuclei

B) The electrostatic forces of an ionic lattice

C) The covalent O-H bonds inside each water molecule

D) The forces of attraction between water molecules

12 / 30

Water has a higher boiling point than methane because water molecules:

A) have no shared electrons

B) are ionic

C) contain weaker covalent bonds

D) form stronger intermolecular attractions

13 / 30

Which substance is most likely to be a simple covalent molecular compound?

A) It remains solid above 3,000°C and forms a network.

B) It contains freely moving electrons in the solid state.

C) It melts at 800°C and consists of positive and negative ions.

D) It melts at 15°C and boils at 80°C.

14 / 30

A substance has a high melting point but does not consist of ions. It is most likely:

A) a liquid hydrocarbon

B) a giant covalent substance

C) a simple molecular substance

D) a noble gas

15 / 30

Diamond has a very high melting point because:

A) its atoms can move freely through the solid

B) strong covalent bonds extend throughout its structure

C) carbon ions form an ionic lattice

D) weak forces act between separate carbon molecules

16 / 30

Which statement correctly compares simple molecular and giant covalent substances?

A) Giant covalent substances require covalent bonds to be broken during melting.

B) Both always have low melting points.

C) Giant covalent substances are held together only by weak forces.

D) Simple molecular substances contain stronger intermolecular forces.

17 / 30

Carbon dioxide is a gas at room temperature, although each molecule contains strong covalent bonds. This is because:

A) carbon dioxide forms a strong ionic lattice

B) the covalent bonds break at room temperature

C) forces between separate CO₂ molecules are weak

D) CO₂ molecules contain charged ions

18 / 30

Which process requires the least energy?

A) Boiling methane

B) Boiling sodium chloride

C) Melting diamond

D) Melting magnesium oxide

19 / 30

A covalent substance has a boiling point higher than that of another covalent substance. The best conclusion is that it has:

A) weaker covalent bonds inside its molecules

B) stronger forces between its particles

C) fewer electrons in every atom

D) smaller nuclear charges in all its atoms

20 / 30

Which sequence shows increasing strength of attraction between particles?

A) Ionic < simple molecular < giant covalent

B) Giant covalent < ionic < simple molecular

C) Simple molecular < giant covalent < weak molecular

D) Simple molecular < ionic < giant covalent

21 / 30

Bromine has a higher boiling point than chlorine mainly because bromine molecules:

A) contain stronger Br-Br bonds that break during boiling

B) form a giant covalent structure

C) are ionic while chlorine molecules are covalent

D) have more electrons and stronger temporary attractions

22 / 30

Which substance would most likely have the highest boiling point?

A) A noble gas atom with few electrons

B) A small non-polar molecule

C) A molecule capable of hydrogen bonding

D) A large non-polar molecule

23 / 30

Two simple molecular substances have similar molecular masses. One is polar and the other is non-polar. The polar substance will generally have:

A) an ionic lattice due to its polarity

B) a lower boiling point because its covalent bonds are weaker

C) the same boiling point because their masses are similar

D) a higher boiling point due to stronger intermolecular attraction

24 / 30

Which observation best indicates strong forces of attraction in a substance?

A) It changes directly into gas easily.

B) It evaporates rapidly at room temperature.

C) It remains liquid over a very low temperature range.

D) It has a high melting and boiling point.

25 / 30

Substance X melts at 25°C, while substance Y melts at 1,200°C. Which conclusion is most reasonable?

A) X must contain stronger particle attractions than Y.

B) Both substances must be simple molecular compounds.

C) Y requires much more energy to overcome its particle attractions.

D) Melting point is unrelated to attractive forces.

26 / 30

Why does an ionic compound remain solid at temperatures at which many molecular compounds become gases?

A) Its ions are connected by weak dispersion forces.

B) Its atoms cannot absorb thermal energy.

C) Its ions have no kinetic energy.

D) Its lattice contains strong attractions in all directions.

27 / 30

Which statement about melting a simple covalent compound is correct?

A) Its molecules gain enough energy to overcome intermolecular forces.

B) Its molecules change into positive and negative ions.

C) Its atomic nuclei separate from their electrons.

D) All covalent bonds within its molecules are broken.

28 / 30

Compound P contains separate molecules and melts at - 20°C. Compound Q forms a continuous covalent network and melts above 1,500°C. The difference is mainly due to:

A) weak intermolecular forces in P but strong network bonds in Q.

B) weaker covalent bonds inside P molecules than inside Q atoms.

C) ionic bonding in P and metallic bonding in Q.

D) the absence of electrons in compound P.

29 / 30

An ionic compound contains M²⁺ and X⁻ ions. Another contains M⁺ and X⁻ ions of similar size. Which compound is expected to have the higher melting point?

A) Both must have identical melting points.

B) The compound containing M²⁺.

C) The compound with the lower total charge.

D) The compound containing M⁺.

30 / 30

Which conclusion about boiling points is scientifically correct?

A) A high boiling point always means strong covalent bonds within molecules.

B) Covalent compounds always boil below room temperature.

C) Ionic compounds boil easily because their ions are charged.

D) Boiling points depend on the forces that must be overcome to separate particles.

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