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Chapter 3 (Chemical bonding), most important short questions. Prepare the best for the exam.

Question 1: What is a chemical bond?
Answer: A chemical bond is defined as the force of attraction between atoms that holds them together in a substance.

Question 2: Why do atoms form chemical bonds?
Answer: Atoms form bonds to achieve stability by attaining the electronic configuration of inert gases (He, Ne, or Ar), which means having ns² np⁶ (2 or 8 electrons) in the valence shell.

Question 3: Why are noble gases non-reactive?
Answer: Noble gases are non-reactive because they are already stable due to the presence of two electrons in helium and eight electrons in the outermost shells of the other noble gases.

Question 4: What is the importance of the noble gas electronic configuration?
Answer: It is a sign of stability; having two or eight electrons in the outermost shell means the atom is stable and hence un-reactive.

Question 5: Define duplet rule.
Answer: Attaining two electrons in the valence shell is called the duplet rule.

Question 6: What is the octet rule?
Answer: Attaining eight electrons in the valence shell is called the octet rule.

Question 7: What are the rules by which atoms complete their valence shells?
Answer: Atoms complete their valence shells through the duplet rule (attaining 2 electrons) or the octet rule (attaining 8 electrons).

Question 8: Which electrons are involved in chemical bonding?
Answer: Only the valence shell electrons are involved in chemical bonding.

Question 9: What are bonding electrons?
Answer: The valence electrons which are involved in chemical bonding are termed as bonding electrons.

Question 10: What is an ionic bond?
Answer: The type of chemical bond which is formed due to the complete transfer of one or more electrons from one atom to another atom is called an ionic bond.

Question 11: Why does sodium form a chemical bond with chlorine?
Answer: Sodium has one electron in its valence shell and tends to lose it, while chlorine has seven and tends to gain one; this transfer stabilizes both and forms a bond.

Question 12: Why does sodium lose an electron and attain a +1 charge?
Answer: Sodium is electropositive in nature and easily loses its valence electron to attain the stable noble gas electronic configuration of Neon.

Question 13: How do atoms follow the octet rule?
Answer: Atoms follow the octet rule by giving valence electrons (if they have 3 or fewer), gaining electrons (if they have 5 or more), or sharing electrons with other atoms.

Question 14: Why do group 1 elements prefer to combine with group 17 elements?
Answer: Group 1 elements are highly electropositive and lose electrons easily, while group 17 elements are highly electronegative and gain electrons easily, leading to ionic bonds through electrostatic attraction.

Question 15: Why can chlorine accept only 1 electron?
Answer: Chlorine has seven electrons in its outermost shell and requires only one more to complete its valence shell and gain the electronic configuration of ¹⁸Ar.

Question 16: Define single covalent bond and give examples.
Answer: A single covalent bond is formed when one electron is contributed by each bonded atom to form one bond pair; examples include H₂, Cl₂, HCl, and CH₄.

Question 17: Define double covalent bond and give examples.
Answer: A double covalent bond is formed when two electrons are contributed by each bonded atom to form two bond pairs; examples include O₂ and C₂H₄.

Question 18: What is meant by a lone pair of electrons?
Answer: The non-bonded electron pair available on an atom in a molecule is called a lone pair, such as the pair on the nitrogen atom in NH₃.

Question 19: What is the difference between a donor and an acceptor?
Answer: A donor is an atom that provides the electron pair for a bond, while an acceptor is the atom that receives it.

Question 20: What is a metallic bond?
Answer: A metallic bond is a bond formed between metal atoms (positively charged ions) due to mobile or free electrons.

Question 21: What types of elements form metallic bonds?
Answer: Metals form metallic bonds because they have low ionization energies and high shielding effects, allowing them to lose electrons easily to form a sea of mobile electrons.

Question 22: Why is the hold of the nucleus over the outermost electrons in metals weak?
Answer: The hold is weak due to the large size of metal atoms, the greater number of shells between the nucleus and valence electrons, and low ionization energy.

Question 23: Why do electrons move freely in metals?
Answer: Electrons move freely because of large atomic sizes and low ionization energy, which lets metal atoms lose their outer electrons easily into common spaces.

Question 24: Which types of electrons are responsible for holding the atoms together in metals?
Answer: Mobile electrons present within the metals are responsible for holding the atoms together.

Question 25: What is the relationship between electropositivity and ionization energy?
Answer: Electropositivity depends on ionization energy; atoms with low ionization energy lose electrons more easily and are more electropositive.

Question 26: What is the atomic size and ionization energy of sodium?
Answer: The atomic size of sodium is 186 pm and its ionization energy is 496 kJ mol^-1.

Question 27: What is the second ionization energy of magnesium?
Answer: The second ionization energy of magnesium is 1450 kJ mol^-1.

Question 28: What is the trend of electropositivity in groups?
Answer: It increases from top to bottom in a group because atomic size increases.

Question 29: What is the trend of electropositivity in periods?
Answer: It decreases from left to right in a period because nuclear charge increases and atomic size decreases.

Question 30: What type of elements are metals?
Answer: Metals are electropositive elements that form cations by losing electrons and typically form basic oxides.

Question 31: What is the nature of a metal oxide?
Answer: Metal oxides are basic in nature because they change red litmus paper to blue.

Question 32: Which group of metal is highly reactive?
Answer: The alkali metals of Group 1 (Li, Na, K, Rb, Cs, Fr) are highly reactive due to their high electropositivity.

Question 33: Why is sodium metal more reactive than magnesium metal?
Answer: Sodium is more reactive because it has a larger atomic size and lower ionization energy than magnesium.

Question 34: Name a metal that can be cut with a knife.
Answer: Sodium metal can be cut with a knife because it is soft due to weak metallic bonding.

Question 35: Name the best ductile and malleable metal.
Answer: Gold is the best ductile and malleable metal.

Question 36: Name the metal that is the poorest conductor of heat.
Answer: Lead (Pb) is the poorest conductor of heat.

Question 37: What do you mean by malleable and ductile?
Answer: Malleability is the property of being beaten into sheets, and ductility is the property of being drawn into wires.

Question 38: Why are alkali metals more reactive than alkaline earth metals?
Answer: Alkali metals have larger atomic sizes and lower ionization energies in their periods, giving them higher metallic character and reactivity.

Question 39: What do you mean by metallic character? / Define electropositivity.
Answer: Metallic character or electropositivity is the tendency of an atom to lose its valence electrons and form positive ions.

Question 40: Why does metallic character decrease along a period and increase in a group?
Answer: It decreases in a period as atomic size decreases and increases in a group as atomic size increases.

Question 41: What is the trend of electronegativity of non-metals?
Answer: Electronegativity is highest for the first members of groups 14-17 and generally decreases down the group (F > O > Cl > N > Br > S > C > I > P).

Question 42: What is non-metallic character?
Answer: Non-metallic character (or electronegative character) is the tendency of an element to gain electrons and form negative ions.

Question 43: Which factors affect the non-metallic character?
Answer: It depends on electron affinity and electronegativity; small atoms with high nuclear charge are more non-metallic.

Question 44: Write properties of covalent compounds.
Answer: They mostly exist as discrete neutral molecules, can be gases or low-boiling liquids, are generally insoluble in water, and are poor conductors.

Question 45: What is the composition of ionic compounds?
Answer: Ionic compounds are composed of positively and negatively charged ions arranged in a crystalline structure.

Question 46: Write any two properties of ionic compounds.
Answer: They are mostly crystalline solids and are good conductors of electricity when in molten form or in solution.

Question 47: Why do ionic compounds have high melting and boiling points?
Answer: They consist of oppositely charged ions held by strong electrostatic forces, requiring great energy to break.

Question 48: Why are ionic compounds easily soluble in water?
Answer: Water is a polar solvent with a high dielectric constant that weakens the attraction between the ions.

Question 49: What type of bond exists in sodium chloride?
Answer: An ionic (or electrovalent) bond exists in sodium chloride.

Question 50: What are intermolecular forces?
Answer: These are the forces of attraction present between the molecules of elements and compounds.

Question 51: Define hydrogen bonding.
Answer: Hydrogen bonding is the attraction between a partially positive hydrogen atom in one molecule and a partially negative atom (N, O, or F) in another.

Question 52: What are dipole-dipole interactions?
Answer: These are attractions between the partial positive end of one polar molecule and the partial negative end of another.

Question 53: Why does a dipole develop in a molecule?
Answer: A dipole develops due to the electronegativity difference between bonded atoms, causing unequal electron sharing.

Question 54: What do you mean by an induced dipole?
Answer: An induced dipole is a temporary dipole produced in a non-polar molecule due to the influence of a nearby polar molecule.

Question 55: Why are dipole forces of attraction not found in halogen molecules?
Answer: Halogens are homoatomic molecules with no electronegativity difference, so they have no dipoles and are non-polar.

Question 56: What types of attractive forces exist between HCl molecules?
Answer: Dipole-dipole forces (intermolecular forces) exist between HCl molecules because they are polar.

Question 57: Define intermolecular forces; show these forces among HCl molecules.
Answer: Intermolecular forces are weak attractions between molecules; in HCl, they appear as H^δ+—Cl^δ- … H^δ+—Cl^δ-.

Question 58: What type of elements lose their outer electron easily and what type gain them easily?
Answer: Metals lose their outer electrons easily to form positive ions, while non-metals gain them easily to form negative ions.

Question 59: Why do lower molecular mass covalent compounds exist as gases or low boiling liquids?
Answer: This is because of the weak intermolecular forces between their molecules.

Question 60: Give one example of an element that exists as a crystalline solid and has covalent bonds.
Answer: Carbon exists as diamond and graphite crystals with covalent bonds between its atoms.

Question 61: Which property of metals makes them malleable and ductile?
Answer: Their layered structure allows layers to slip past each other when pressure is applied while remaining intact due to the metallic bond.

Question 62: Is a coordinate covalent bond a strong bond?
Answer: No, it is generally a weaker bond compared to a simple covalent bond.

Question 63: Write down the dot and cross formula of HNO₃.
Answer: The dot and cross formula shows the electron distribution where hydrogen, nitrogen, and oxygen atoms share or donate electron pairs to achieve stability.

Question 64: Why is HF a liquid while HCl is a gas?
Answer: HF is a liquid due to strong hydrogen bonding, while HCl has much weaker dipole-dipole forces.

Question 65: Why are covalent compounds not soluble in water?
Answer: Most covalent compounds are non-polar and lack a strong attraction to polar water molecules.

Question 66: How do metals conduct heat?
Answer: Metals conduct heat due to the presence of mobile electrons throughout their crystal lattice.

Question 67: How many oxides does nitrogen form? Write their formulas.
Answer: Nitrogen forms five oxides: N₂O, NO, NO₂, N₂O₃, and N₂O₅.

Question 68: What will happen if NaBr is treated with AgNO₃ in water?
Answer: A white precipitate of AgBr (silver bromide) forms along with NaNO₃.

Question 69: Why does iodine exist as a solid while Cl₂ exists as a gas?
Answer: Iodine has a larger atomic size and more contact surface for intermolecular forces than chlorine.

Question 70: How do ions arrange themselves to form NaCl crystals?
Answer: Oppositely charged ions (Na⁺ and Cl^–) are held by electrostatic forces and surround each other three-dimensionally in a crystal lattice.

Question 71: How will you explain the electrical conductivity of graphite crystals?
Answer: Graphite conducts electricity because it has delocalized or free-moving electrons within its layered carbon structure.

Question 72: Why are metals usually hard and heavy?
Answer: Metal atoms are strongly held and arranged in closely packed rows, which makes them dense and hard.

Question 73: The formula of AlCl₃ in vapour phase is Al₂Cl₆. Explain the bonding between its molecules.
Answer: In the dimer Al₂Cl₆, a chlorine atom from each AlCl₃ molecule donates a lone pair to the aluminum center of the other molecule, forming coordinate covalent bonds.

Question 74: Explain the structure of sand (SiO₂).
Answer: Sand has a tetrahedral structure where each silicon atom is covalently bonded to four oxygen atoms in a three-dimensional network solid.

Question 75: What is the trend of electropositivity in a period?
Answer: Electropositivity decreases from left to right across a period as the nuclear charge increases and atomic size decreases.

Question 76: Define a coordinate covalent bond.
Answer: A coordinate covalent bond is a type of covalent bond in which the shared electron pair is donated by one atom only.