IBDP Chemistry - Structure 2.1 The ionic model- IB Style Questions For SL Paper 1A - FA 2025
▶️ Answer/Explanation
1. Determine Ionic Charges:
- Calcium (Group 2) forms \(Ca^{2+}\) ions.
- Nitrogen (Group 15) forms \(N^{3-}\) ions.
2. Determine Formula:
To balance charges: \(3 \times (+2) + 2 \times (-3) = 0\). The formula is \(Ca_{3}N_{2}\). This eliminates A and B.
3. Determine Electron Configurations of Ions:
- \(Ca^{2+}\): Calcium (\([Ar]4s^2\)) loses 2 electrons \(\rightarrow\) \([Ar]\).
- \(N^{3-}\): Nitrogen (\([He]2s^22p^3\)) gains 3 electrons \(\rightarrow\) \([He]2s^22p^6\), which is isoelectronic with Neon \([Ne]\).
4. Match to Options:
Formula \(Ca_{3}N_{2}\), Ca species \([Ar]\), N species \([Ne]\).
✅ Answer: (D)
▶️ Answer/Explanation
The configuration \(1s^{2}\,2s^{2}\,2p^{3}\) corresponds to an atom with \[ 2 + 2 + 3 = 7 \] electrons (nitrogen). Its valence-shell configuration is \[ 2s^{2}\,2p^{3}, \] which gives \(5\) valence electrons.
To achieve a stable octet (\(8\) valence electrons), the atom will gain: \[ 8 – 5 = 3 \text{ electrons}. \]
Therefore, when forming an ionic bond, this element gains three electrons.
✅ Answer: (D)
▶️ Answer/Explanation
Ionic compounds consist of positive and negative ions held together by strong electrostatic attractions in an ionic lattice. These strong forces give ionic substances:
- High melting points (a lot of energy is needed to break the lattice).
- Electrical conductivity in the liquid (molten) state, because ions become mobile and can carry charge.
Among the options, only substance D has both a high melting point and conducts electricity in the liquid state, matching the typical properties of an ionic lattice.
✅ Answer: (D)