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Atoms, Elements and Compounds - Ionic bonding

Grade 12A LevelChemistry

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

🔑Concepts

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Ionic bonding is the strong electrostatic attraction between oppositely charged ions (cationscations and anionsanions).

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It typically occurs between metals and non-metals through the transfer of valence electrons to achieve a stable noble gas electronic configuration (the octet rule).

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Metals undergo oxidation to form positive ions: M→Mn++ne−M \rightarrow M^{n+} + ne^-. For example, Na→Na++e−Na \rightarrow Na^+ + e^-.

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Non-metals undergo reduction to form negative ions: X+ne−→Xn−X + ne^- \rightarrow X^{n-}. For example, Cl+e−→Cl−Cl + e^- \rightarrow Cl^-.

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Ionic compounds form a giant ionic lattice, a regular 3D3D arrangement where every positive ion is surrounded by negative ions and vice versa.

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Physical properties include high melting and boiling points due to the large amount of energy needed to break the strong electrostatic forces in the lattice.

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Ionic compounds are brittle because a blow can shift the layers of ions, causing ions of the same charge to align and repel each other.

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They conduct electricity only when molten or in aqueous solution (electrolyteselectrolytes) because the ions are free to move; in solid state, ions are fixed in the lattice.

📐Formulae

F=kq1q2r2F = k \frac{q_1 q_2}{r^2} (Coulombic force of attraction between ions)

M(s)→Mn+(g)+ne−M(s) \rightarrow M^{n+}(g) + ne^- (Ionization energy process)

Net Charge=∑(positive charges)+∑(negative charges)=0\text{Net Charge} = \sum (\text{positive charges}) + \sum (\text{negative charges}) = 0

U∝z+z−r++r−U \propto \frac{z_+ z_-}{r_+ + r_-} (Lattice energy relationship)

💡Examples

Problem 1:

Explain the formation of Magnesium Chloride and provide its chemical formula.

Solution:

Magnesium (MgMg) is in Group 2 and has the configuration [Ne]3s2[Ne] 3s^2. It loses 22 electrons to form Mg2+Mg^{2+}. Chlorine (ClCl) is in Group 17 and has the configuration [Ne]3s23p5[Ne] 3s^2 3p^5. Each ClCl atom gains 11 electron to form Cl−Cl^-. To balance the charges, one Mg2+Mg^{2+} ion reacts with two Cl−Cl^- ions, resulting in MgCl2MgCl_2.

Explanation:

The total positive charge (+2+2) must equal the total negative charge (2×−1=−22 \times -1 = -2) to ensure the compound is electrically neutral.

Problem 2:

Predict whether MgOMgO or NaClNaCl has a higher melting point and justify your answer.

Solution:

MgOMgO has a significantly higher melting point than NaClNaCl.

Explanation:

Melting point depends on the strength of the ionic bond (lattice energy). In MgOMgO, the ions are Mg2+Mg^{2+} and O2−O^{2-}, while in NaClNaCl they are Na+Na^+ and Cl−Cl^-. Since the product of the charges in MgOMgO (2×2=42 \times 2 = 4) is greater than in NaClNaCl (1×1=11 \times 1 = 1), and the ionic radii are smaller, the electrostatic attraction is much stronger in MgOMgO.