9.3.10 Nature of Bonding and Properties
This is the tenth lecture from Chapter 3: “Chemical Bonding” in the new Class 9 Chemistry book (Punjab Board – PCTB). It discusses the nature of ionic and covalent bonding along with different properties of ionic compounds and covalent compounds. The lecture also includes a multiple-choice quiz, short question and long question notes.
MCQs Based Quiz
Short Questions
Q1. Write some properties of ionic compounds.
- Ionic compounds form a crystal lattice in which oppositely charged ions are held strongly by electrostatic forces of attraction.
- In this crystal lattice ions are held very firmly, which gives ionic compound very high melting and boiling points.
Q2. Why do we say that ionic compounds are brittle?
Ionic compounds are brittle because an external force on the crystal lattice can easily breaks it.
Q3. Why don’t solid ionic compounds conduct electricity?
Solid state of ionic compounds does not conduct electricity because it contains tightly held ions which cannot move.
Q4. Why do molten ionic compounds and their solutions conduct electricity?
Their molten state and aqueous solutions can easily conduct electricity due to free ions. Because in these forms, free ions can move towards respective electrodes.
Q5. Why do ionic compounds generally dissolve in water?
Ionic compounds are generally soluble in water because water molecules can break the electrostatic forces (ionic bonds) and hydrate the free ions. In hydration, water molecules surround the ions and keep them separated.
Q6. What happens if mix two solutions of ionic compounds?
When two ionic solutions are mixed in water, they often undergo exchange reactions, in which they swap ions and form two new ionic compounds.
$\ce{NaCl_{(aq)} + AgNO3_{(aq)} -> NaNO3_{(aq)} + AgCl_{(s)}}$
Q7. What are the applications of molten form and aqueous solutions of ionic compounds?
- Electrolysis of molten NaCl produces sodium metal (Na) and chlorine gas (Cl2).
- Electrolysis of aqueous NaCl yields sodium hydroxide (NaOH) and chlorine gas (Cl2).
Q8. Write some properties of covalent compounds.
- Molecular substances generally have weak intermolecular forces, which results in low densities and low melting and boiling points.
- These solid covalent compounds can exist in both forms, i.e., amorphous and crystalline.
Q9. What is coal?
Coal is an amorphous form of carbon which is used as fuel in electricity generation plants.
Q10. What is graphite?
Graphite is a crystalline form of carbon which consists of connected layers of hexagonal rings of carbon atoms.
Q11. What are the uses of graphite?
- Graphite is also a crystalline form of carbon, consisting of connected layers of hexagonal rings of carbon atoms.
- Due to the presence of free electrons between layers, graphite is a good conductor of electricity and is used as an electrode in batteries and in electric arc furnaces to produce steel.
Q12. What is diamond?
Diamond is a crystalline form of carbon in which each carbon atom forms strong covalent bonds with other four carbon atoms.
Q13. What are the uses of diamonds?
- Due to this their rigid structure, diamonds are one of the hardest things on planet.
- They are used in cutting, polishing and drilling tool.
Q14. Why do covalent compounds like nitrogen (N₂) and oxygen (O₂) have low boiling points?
They have low boiling points because they have very weak forces of attraction between their molecules.
Q15. What is the physical state of bromine (Br₂) at room temperature?
Bromine exists as volatile fuming liquid at room temperature.
Q16. Name two elements that exist as covalent solids.
Oxygen (O2) and bromine (Br2) are two elements that exist as covalent solids.
Q17. What are some amorphous and crystalline forms of carbon element?
Coal is an amorphous form of carbon element. Whereas graphite and diamond are crystalline forms.
Q18. Why is diamond the hardest substance on Earth?
In diamond, each carbon atom is strongly bonded to four other carbon atoms. This strong interconnected bonding gives diamond their rigid and hard structure.
Q19. Describe the structure of graphite.
Graphite consists of a layered structure made of hexagonal rings of carbon atoms.
Q20. Describe the structure of a diamond.
A diamond is made of carbon atoms, where each carbon atom is strongly bonded to four other carbon atoms, forming a rigid structure.
Q21. Why can layers in graphite slip past each other?
Layers in graphite are not strongly bonded with each other. Therefore, they can slip past each other. Which makes it a good lubricant.
Q22. What property of graphite makes it useful as a lubricant?
In graphite, the layers are not strongly bonded to one another. Therefore, they can easily slip past each other, which makes graphite a good lubricant.
Q23. Why is graphite a good conductor of electricity?
Graphite contains mobile electrons within its layers. These electrons are free to move, allowing graphite to conduct electricity.
Q24. Which covalent compound of carbon can be used as an electrode and why?
Graphite can be used as an electrode because it contains mobile electrons, which make it a good conductor of electricity. It is used in batteries and electric arc furnaces for steel production.
Q25. What is the general physical state of binary covalent compounds at room temperature?
Binary covalent compounds generally exist as low temperature boiling gases (except water).
Q26. Name three covalent compounds that are gases at room temperature.
Methane (CH4), hydrogen chloride (HCl), ammonia (NH3) and hydrogen sulphide (H2S) are some covalent compounds that are gases at room temperature.
Q27. Why is water a liquid at room temperature while most other covalent compounds are gases?
Water is a liquid at room temperature because it has strong hydrogen bonding unlike the weak intermolecular forces present in most other covalent compounds.
Q28. What is the reason for water’s high boiling point?
Water has high boiling point because it has a strong hydrogen bonding between its molecules.
Q29. Name two covalent compounds that are liquids at room temperature.
Water (H2O) and hydrogen fluoride (HF) are two covalent compounds that are liquid at room temperature.
Q30. What happens to hydrogen chloride when it dissolves in water?
Hydrogen chloride (HCl) acts as a strong acid and ionizes completely in water.
$\ce{
HCl_{(aq)} \overset{H_2O}{\rightleftharpoons} {H^{+}}_{(aq)} + {Cl^{-}}_{(aq)}
}$
Q31. Why are sulfuric acid and nitric acid considered strong acids in water?
This is because they ionize completely in water.
For example sulfuric acid dissolves completely in water:
$\ce{
H_2SO_4_{(aq)} \overset{H_2O}{\rightleftharpoons} {2H^{+}}_{(aq)} + {SO_4^{-}}_{(aq)}
}$
Q32. How do covalent compounds differ from ionic compounds in terms of behavior?
Covalent Compounds
Ionic Compounds
Covalent compounds generally have low melting and boiling points.
Ionic compounds have very high melting and boiling points.
They have low densities.
Densities of ionic compounds are very high.
They exist in all three common states of matter.
Ionic compounds only exist as solids.
Descriptive Question
Q1. Write down all the properties of ionic compounds.
Properties of Ionic Compounds:
- Ionic compounds form a crystal lattice in which opposite ions are held tightly by an electrostatic force of attraction.
- The strong ionic bonds in the crystal lattice result in very high melting and boiling points.
- Due to the spherical shape of ions, oppositely charged ions can attract each other from all directions. This makes ionic bonds non-directional.
- Ionic compounds are highly brittle, because an external force can easily break the crystal lattice.
- In solid form, ionic compounds do not conduct electricity because their ions are tightly held and cannot move freely.
- In molten form or aqueous solution, ionic compounds conduct electricity due to the presence of free, mobile ions that move towards the respective electrodes.
- Ionic compounds are generally soluble in water. Water molecules can overcome the strong electrostatic forces and surround (hydrate) the individual ions, keeping them apart in solution.
- In aqueous solution, ionic compounds can undergo exchange (double displacement) reactions, where they swap ions to form two new compounds.
$\ce{NaCl_{(aq)} + AgNO3_{(aq)} -> NaNO3_{(aq)} + AgCl_{(s)}}$
Q2. List down all the properties of molecular substances
Properties of Molecular Substances:
- Most elements on the right side of the periodic table (except noble gases) exist as covalently bonded diatomic molecules. For example, nitrogen (N2), oxygen (O2), fluorine (F2) and chlorine (Cl2).
- Molecular substances generally have weak intermolecular forces, which results in low densities and low melting and boiling points.
- Bromine (Br2) exists as volatile liquid, while elements like carbon, phosphorus and sulphur exist as covalent solids.
- These solid covalent compounds can exist in both forms, i.e., amorphous and crystalline.
- Covalent compounds such as hydrogen chloride, sulphuric acid and nitric acid ionize completely in water behaving as very strong acids.
$\ce{
HCl_{(aq)} \overset{H_2O}{\rightleftharpoons} {H^{+}}_{(aq)} + {Cl^{-}}_{(aq)}
}$
Q3. Write down a comprehensive note on amorphous and crystalline forms of carbon element.
Coal:
Coal is an amorphous form of carbon used as a fuel in electricity generation plants.
Diamond:
- Diamond is a crystalline form of carbon in which each carbon atom forms strong covalent bonds with four other carbon atoms.
- Due to this rigid structure, diamonds are one of the hardest things on planet.
- It is used in cutting, polishing and drilling tool.
- Diamond tipped glass cutter are used to make clean cuts in glass.
- Diamond-tipped drills bits are used to drill through hard rocks in mining operations.
Graphite:
- Graphite is also a crystalline form of carbon, consisting of connected layers of hexagonal rings of carbon atoms.
- These layers are weakly bonded and can slip past each other, making graphite useful as a lubricant in industries.
- Due to the presence of free electrons between layers, graphite is a good conductor of electricity and is used as an electrode in batteries and in electric arc furnaces to produce steel.
- It is also used in pencils, polishes and making crucibles.
Q4. What are binary compounds? Explain in detail.
Compounds made of only two types of atoms are called binary covalent compounds.
- Methane (CH4), ammonia (NH3), hydrogen sulphide (H2S), hydrogen chloride (HCl), nitrogen dioxide (NO2), carbon dioxide (CO2) and sulphur dioxide (SO2) are all gases at room temperature. All of these boils at very low temperatures.
- Water (H2O) and hydrogen fluoride (HF) are liquids at room temperature.
- Water has a very high boiling point due to strong hydrogen bonding.
- Binary compounds such as hydrogen chloride ionize completely in water behaving as very strong acids.
$\ce{
HCl_{(aq)} \overset{H_2O}{\rightleftharpoons} {H^{+}}_{(aq)} + {Cl^{-}}_{(aq)}
}$
Explain the behaviour of ionic compounds in water.
Hydration of Ionic Compounds:
Ionic compounds are generally soluble in water. This is because water breaks the strong electrostatic force of attraction and hydrates the free ions. Hydration is a process in which free ions from an ionic compound are surrounded by water molecules.
Exchange Reaction of Ionic Compounds:
When two ionic compounds are dissolved in water, they exchange their positive and negative ions, which results in the formation of new ionic compounds. For example, in NaCl and NaNO3 are dissolved in the water, they will exchange their cations and anions. This will result in the formation of AgCl, which is insoluble in water and precipitates out of the solution.
Electrical Conduction in Aqueous Solution:
When ionic compounds are dissolved in water, their ions become mobile. Due to these mobile ions, aqueous solutions of ionic compounds can conduct electricity. For example, in industries, the electrolysis of aqueous solution of NaCl is used to produce sodium hydroxide (NaOH) and chlorine gas (Cl2).