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) Strong electrostatic forces act between oppositely charged ions.

B) Their ions are joined by weak intermolecular forces.

C) Their ions move freely in the solid state.

D) Their atoms contain a large number of neutrons.

2 / 30

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

A) its atoms are arranged in an ionic lattice

B) its molecules contain no electrons

C) its covalent bonds break easily

D) weak forces exist between its molecules

3 / 30

Which substance is expected to have the highest melting point?

A) Carbon dioxide, CO₂

B) Chlorine, Cl₂

C) Methane, CH₄

D) Sodium chloride, NaCl

4 / 30

When sodium chloride melts, which forces are mainly overcome?

A) Metallic bonds between sodium ions

B) Covalent bonds between sodium and chlorine atoms

C) Nuclear forces inside the ions

D) Electrostatic attractions between Na⁺ and Cl⁻ ions

5 / 30

Which statement correctly explains the low boiling point of methane?

A) Methane contains weak forces between its molecules

B) Carbon–hydrogen covalent bonds break during boiling

C) Methane has a giant covalent structure

D) Methane molecules have strong ionic attractions

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) MgO contains molecules larger than NaCl molecules.

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

C) MgO has weaker electrostatic attractions.

D) NaCl contains stronger covalent bonds.

8 / 30

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

A) K⁺ and Br⁻

B) Na⁺ and Cl⁻

C) Li⁺ and F⁻

D) Mg²⁺ and O²⁻

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) no attraction between its ions

C) stronger attraction and a higher melting point

D) weaker attraction and a higher boiling point

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) LiF

D) Both have exactly the same attraction

11 / 30

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

A) The electrostatic forces of an ionic lattice

B) The bonds inside oxygen nuclei

C) The forces of attraction between water molecules

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

12 / 30

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

A) form stronger intermolecular attractions

B) are ionic

C) have no shared electrons

D) contain weaker covalent bonds

13 / 30

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

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

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

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

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

14 / 30

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

A) a giant covalent substance

B) a noble gas

C) a liquid hydrocarbon

D) a simple molecular substance

15 / 30

Diamond has a very high melting point because:

A) weak forces act between separate carbon molecules

B) its atoms can move freely through the solid

C) carbon ions form an ionic lattice

D) strong covalent bonds extend throughout its structure

16 / 30

Which statement correctly compares simple molecular and giant covalent substances?

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

B) Both always have low melting points.

C) Simple molecular substances contain stronger intermolecular forces.

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

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) CO₂ molecules contain charged ions

D) forces between separate CO₂ molecules are weak

18 / 30

Which process requires the least energy?

A) Boiling methane

B) Melting diamond

C) Boiling sodium chloride

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) smaller nuclear charges in all its atoms

C) stronger forces between its particles

D) fewer electrons in every atom

20 / 30

Which sequence shows increasing strength of attraction between particles?

A) Giant covalent < ionic < simple molecular

B) Simple molecular < ionic < giant covalent

C) Ionic < simple molecular < giant covalent

D) Simple molecular < giant covalent < weak molecular

21 / 30

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

A) form a giant covalent structure

B) are ionic while chlorine molecules are covalent

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

D) have more electrons and stronger temporary attractions

22 / 30

Which substance would most likely have the highest boiling point?

A) A large non-polar molecule

B) A molecule capable of hydrogen bonding

C) A small non-polar molecule

D) A noble gas atom with few electrons

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) a lower boiling point because its covalent bonds are weaker

B) the same boiling point because their masses are similar

C) an ionic lattice due to its polarity

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 remains liquid over a very low temperature range.

B) It has a high melting and boiling point.

C) It changes directly into gas easily.

D) It evaporates rapidly at room temperature.

25 / 30

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

A) Both substances must be simple molecular compounds.

B) Melting point is unrelated to attractive forces.

C) X must contain stronger particle attractions than Y.

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

26 / 30

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

A) Its lattice contains strong attractions in all directions.

B) Its ions have no kinetic energy.

C) Its atoms cannot absorb thermal energy.

D) Its ions are connected by weak dispersion forces.

27 / 30

Which statement about melting a simple covalent compound is correct?

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

B) All covalent bonds within its molecules are broken.

C) Its molecules change into positive and negative ions.

D) Its atomic nuclei separate from their electrons.

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

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

C) weak intermolecular forces in P but strong network bonds 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) The compound containing M⁺.

B) The compound with the lower total charge.

C) The compound containing M²⁺.

D) Both must have identical melting points.

30 / 30

Which conclusion about boiling points is scientifically correct?

A) Covalent compounds always boil below room temperature.

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

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

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

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