STRUCTURE 3
Classification of Matter
PERIODIC TABLE • TRENDS • ORGANIC FUNDAMENTALS
3.1 The Periodic Table
1. The Architecture of the Table
The Periodic Table is a map of electron configurations.
- Groups (Vertical 1–18): Share the same number of valence electrons.
Consequence: Similar chemical properties. - Periods (Horizontal 1–7): Period number ($n$) = outer principal energy level.
- Blocks ($s, p, d, f$): Based on which sub-shell contains the highest-energy electron.
2. Periodicity: Physical Trends
Explain trends using the battle between Nuclear Charge (pulling in) and Shielding (pushing out).
| Trend | Across Period ($\rightarrow$) | Down Group ($\downarrow$) | The "Why" |
|---|---|---|---|
| Atomic Radius | Decreases | Increases |
Across: Nuclear charge $\uparrow$, shielding constant. Nucleus pulls closer. Down: New shells added. Valence $e^-$ further away. |
| Ionization Energy | Increases | Decreases |
Across: Harder to remove $e^-$ due to stronger pull. Down: Easier to remove due to distance/shielding. |
| Electronegativity | Increases | Decreases | Fluorine is King (4.0). Ability to attract a bonding pair. |
Examiner Tip
When comparing isoelectronic ions (e.g., $N^{3-}, O^{2-}, F^-, Na^+, Mg^{2+}$), the one with the most protons ($Mg^{2+}$) is the smallest because it has the strongest pull.
3. Period 3 Oxides
3.2 Organic Fundamentals
1. Representations & Nomenclature
Organic chemistry is the study of carbon frameworks.
IUPAC Naming
PREFIX + STEM + SUFFIX
Meth(1), Eth(2), Prop(3), But(4), Pent(5), Hex(6).
-ane, -ene, -ol, -anal, -anone, -oic acid.
Trap Alert
You must draw H atoms if they are attached to heteroatoms (like O or N). Don't leave an $-OH$ group as just $-O$.
2. The Homologous Series
A "family" with the same Functional Group and General Formula.
Trend: Chain length $\uparrow$ = Boiling Point $\uparrow$ (Stronger London Dispersion Forces).
3. Structural Isomerism
Same molecular formula but different structural arrangements (connectivity).
Ex: Butane vs 2-methylpropane.
Advanced Theory
Warning: The following content is required for HL students only. Concepts include Advanced Periodicity and Organic Spectroscopy.
3.1 Advanced Periodicity
1. Ionization Energy Discontinuities
Trend "blips" prove sub-shells exist.
B's electron is in the 2p orbital (higher energy than 2s), so easier to remove.
O has a paired electron in p-orbital. Spin-pair repulsion makes it easier to remove.
2. Transition Elements (d-block)
Definition: Element with an incomplete d-sublevel in atom or stable ion.
Zinc (Zn) is NOT a transition metal ($3d^{10}$). It is colorless and diamagnetic.
Origin of Color (3 Marks)
- Ligands cause d-orbital splitting.
- Electrons absorb visible light to move to higher level (d-d transition).
- Observed color is the complementary color.
3.2 Advanced Organic Analysis
1. Stereoisomerism
- Cis-Trans / E-Z: Caused by restricted rotation around bond.
- Optical: Requires a Chiral Carbon (4 diff groups). Forms Enantiomers.
2. Spectroscopy
| Method | Key Info |
|---|---|
| Mass Spec (MS) | Highest peak ($M^+$) = Molar Mass. |
| Infrared (IR) | Detects bonds. O-H (broad 3200-3600), C=O (sharp 1700). |
| Proton NMR ($^1H$) | Splitting ($N+1$ Rule): Neighbors + 1. 0 neighbors $\to$ Singlet | 2 $\to$ Triplet. |
The Examiner's Vault
Strictly assessed on Structure 3 content.
Isoelectronic series. Sulfur has the lowest proton number (16), so the nucleus pulls the least, allowing the cloud to expand.
Compound $C_3H_6O$ shows sharp IR absorption at $1720 \, cm^{-1}$ and a singlet in $^1H$ NMR. Identify it.
1720 = C=O group. Singlet = All 6 Hydrogens are equivalent/no neighbors. Propanone ($CH_3-CO-CH_3$) fits.
Write the equation for $P_4O_{10}$ + water, and compare the pH of the solution to that of $Na_2O$ + water.
- (a) $P_4O_{10} + 6H_2O \rightarrow \mathbf{4H_3PO_4}$ [1]
- (b) $Na_2O$ forms a basic solution (pH 12-14). $P_4O_{10}$ forms an acidic solution (pH 0-2). [1]
Explain why $[Fe(H_2O)_6]^{3+}$ is colored, whereas $Sc^{3+}$ is colorless.
- $Fe^{3+}$ has a partially filled d-sublevel ($3d^5$). [1]
- Ligands cause d-orbital splitting allowing $e^-$ to absorb visible light (d-d transitions). [1]
- $Sc^{3+}$ has an empty d-sublevel ($3d^0$), so no transitions possible. [1]