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Chemistry - Chemical Bonding

Grade 10ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Chemical Bond: It is the force of attraction between any two atoms in a molecule to maintain stability. Atoms bond to achieve the stable electronic configuration of the nearest noble gas (octet or duplet rule).

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Electrovalent (Ionic) Bonding: Formed by the complete transfer of one or more electrons from a metallic atom to a non-metallic atom. Resulting ions are held by strong electrostatic forces. Example: NaClNaCl, MgCl2MgCl_2, CaOCaO.

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Covalent (Molecular) Bonding: Formed by the mutual sharing of electrons between two non-metallic atoms. Bonds can be single (share 11 pair), double (share 22 pairs), or triple (share 33 pairs).

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Polar and Non-Polar Covalent Bonds: Non-polar bonds occur between identical atoms (e.g., H2H_2, Cl2Cl_2) where electrons are shared equally. Polar bonds occur between atoms with different electronegativities (e.g., HClHCl, H2OH_2O), causing partial charges δ+\delta^+ and δ−\delta^-.

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Coordinate (Dative) Bonding: A special type of covalent bond where both electrons of the shared pair come from only one of the two atoms. It is represented by an arrow →\rightarrow. Examples include NH4+NH_4^+ and H3O+H_3O^+.

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Conditions for Ionic Bond: Low Ionization Potential for the metal, High Electron Affinity for the non-metal, and a large electronegativity difference (ΔEN>1.7\Delta EN > 1.7).

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Properties of Ionic Compounds: High melting/boiling points, soluble in water but insoluble in organic solvents, and conduct electricity in molten or aqueous states.

📐Formulae

M−ne−→Mn+ (Cation formation)M - ne^- \rightarrow M^{n+} \text{ (Cation formation)}

X+ne−→Xn− (Anion formation)X + ne^- \rightarrow X^{n-} \text{ (Anion formation)}

Mn++Xn−→MX (Electrovalent Bond)M^{n+} + X^{n-} \rightarrow MX \text{ (Electrovalent Bond)}

H2O+H+→[H3O]+ (Hydronium Ion formation)H_2O + H^+ \rightarrow [H_3O]^+ \text{ (Hydronium Ion formation)}

NH3+H+→[NH4]+ (Ammonium Ion formation)NH_3 + H^+ \rightarrow [NH_4]^+ \text{ (Ammonium Ion formation)}

💡Examples

Problem 1:

Show the formation of Magnesium Chloride (MgCl2MgCl_2) using Lewis electron dot structure.

Solution:

Magnesium (MgMg, Z=12Z=12): [2,8,2][2, 8, 2]. Chlorine (ClCl, Z=17Z=17): [2,8,7][2, 8, 7]. Mg⋅⋅+2[⋅Cl¨⋅]→[Mg]2+[:Cl¨:]2−Mg \cdot \cdot + 2[\cdot \ddot{\text{Cl}} \cdot] \rightarrow [Mg]^{2+} [:\ddot{\text{Cl}}:]^-_2

Explanation:

Magnesium loses 22 electrons to achieve an octet, forming Mg2+Mg^{2+}. Two Chlorine atoms each gain 11 electron to form two Cl−Cl^- ions. The electrostatic attraction between Mg2+Mg^{2+} and 2Cl−2Cl^- forms the ionic compound MgCl2MgCl_2.

Problem 2:

Explain the bonding in a Nitrogen molecule (N2N_2).

Solution:

Nitrogen (NN, Z=7Z=7): [2,5][2, 5]. Needs 33 electrons to complete octet. :N⋮N:→N≡N:N \vdots N: \rightarrow N \equiv N

Explanation:

Each Nitrogen atom contributes three electrons to form three shared pairs. This results in a triple covalent bond (N≡NN \equiv N), making the molecule very stable.

Problem 3:

Describe the formation of the Hydronium ion (H3O+H_3O^+).

Solution:

H2O+H+→[H3O]+H_2O + H^+ \rightarrow [H_3O]^+

Explanation:

The Oxygen atom in the polar water molecule (H2OH_2O) has two lone pairs of electrons. When it reacts with a Hydrogen ion (H+H^+), which has no electrons, Oxygen donates one lone pair to form a coordinate bond with H+H^+, resulting in [H3O]+[H_3O]^+.