Short Answer Questions:
i. What type of elements lose their outer electron easily and what type of elements gain electrons easily?
- Elements that lose electrons easily: Metals, particularly those in groups 1 and 2 (alkali and alkaline earth metals), readily lose their outer electrons to achieve stability.
- Elements that gain electrons easily: Non-metals, such as halogens, tend to gain electrons to achieve a stable electron configuration resembling noble gases.
ii. Why do lower molecular mass covalent compounds exist as gases or low-boiling liquids?
Explanation: Compounds with lower molecular masses typically have weaker intermolecular forces (like Van der Waals forces). These forces are easy to overcome with minimal energy, which results in a lower boiling point, allowing these substances to exist as gases or liquids at room temperature.
iii. Give one example of an element that exists as a crystalline solid and has covalent bonds in its atoms.
Example: Diamond (a form of carbon) exists as a crystalline solid, with each carbon atom covalently bonded to four others, creating a rigid structure.
iv. Which property of metals makes them malleable and ductile?
Explanation: The ability of metals to be malleable (hammered into sheets) and ductile (drawn into wires) arises from the nature of metallic bonding. The delocalized electrons form a "sea" of electrons that allow metal atoms to slide past each other without breaking the bonds, making metals flexible.
v. Is a coordinate covalent bond a strong bond?
Explanation: Yes, a coordinate covalent bond is a strong bond. After its formation, it behaves exactly like a regular covalent bond, with both atoms contributing electrons.
vi. Write down the dot and cross formula of HNO₃.
Dot and Cross Formula of HNO₃:
H : O : N : : O
. . . .
. . O
This formula shows how electrons are shared between the atoms, where nitrogen is at the center, bonded to one hydrogen through oxygen, and two other oxygen atoms, one of which forms a double bond.
3. Constructed Response Questions:
i. Why is HF a liquid while HCl is a gas?
Explanation: HF (Hydrogen Fluoride) has strong hydrogen bonding due to the high electronegativity of fluorine. These bonds are stronger than the dipole-dipole interactions in HCl, making HF a liquid at room temperature, while HCl is a gas.
ii. Why are covalent compounds generally not soluble in water?
Explanation: Water is a polar solvent, and covalent compounds are often non-polar. Since "like dissolves like," non-polar covalent compounds do not interact effectively with polar water molecules, making them insoluble in water.
iii. How do metals conduct heat?
Explanation: Metals conduct heat through their free-moving electrons. When one part of the metal is heated, the kinetic energy of the electrons increases, and these energetic electrons spread the heat throughout the material by transferring energy to other electrons and metal ions.
iv. How many oxides does nitrogen form? Write down the formulae of oxides.
Explanation: Nitrogen forms several oxides, including:
- N₂O (Nitrous oxide)
- NO (Nitric oxide)
- N₂O₃ (Dinitrogen trioxide)
- NO₂ (Nitrogen dioxide)
- N₂O₄ (Dinitrogen tetroxide)
- N₂O₅ (Dinitrogen pentoxide)
v. What will happen if NaBr is treated with AgNO₃ in water?
Explanation: A precipitation reaction will occur, forming silver bromide (AgBr) as a pale yellow solid.
Reaction:
NaBr(aq) + AgNO₃(aq) → AgBr(s) + NaNO₃(aq)
vi. Why does iodine exist as a solid while Cl₂ exists as a gas?
Explanation: Iodine (I₂) has stronger intermolecular forces (London dispersion forces) compared to chlorine (Cl₂) because iodine has a larger atomic size and more electrons. These stronger forces cause iodine to be a solid at room temperature, while chlorine remains a gas.
4. Descriptive Questions:
i. Explain the formation of an ionic bond and a covalent bond.
- Ionic Bond: An ionic bond forms when one atom transfers an electron to another, creating oppositely charged ions that attract each other. This typically happens between metals (which lose electrons) and non-metals (which gain electrons).
- Covalent Bond: A covalent bond is formed when two atoms share electrons to achieve a stable electron configuration. This typically occurs between non-metal atoms.
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