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Flashcards · IB Diploma Programme Chemistry · Topic 3

Structure 3 – Classification of matter flashcards

23 cards on Topic 3, subtopics 3.1 to 3.2. Pick a subtopic or study them all.

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3.1 The periodic table: Classification of elements

Period and group from an electron configuration
Period = outer occupied main level (n). Group = number of valence electrons for groups 1 and 2; group number minus 10 for groups 13 to 18. The block shows which sublevel is filling.
First ionization energy
The energy, per mole, to take the outermost electron from each atom of a gaseous element in its ground state, giving gaseous 1+ ions.
Electron affinity
The energy change, per mole, as each gaseous atom picks up one electron to become a gaseous 1− ion.
Periodic trends: the explanation across a period
More protons, same main level, similar shielding → outer electrons pulled harder.
Periodic trends: the explanation down a group
Extra main level, more shielding → outer electrons further away and held less tightly.
Order the radii of N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺
N³⁻ > O²⁻ > F⁻ > Na⁺ > Mg²⁺. All have 10 electrons; more protons pull them in more tightly.
Ocean acidification
Extra CO₂ dissolves → H₂CO₃ ⇌ H⁺ + HCO₃⁻ → pH falls; H⁺ removes CO₃²⁻ as HCO₃⁻, so less carbonate is available for shells.
Oxidation state of iodine in HIO₃
(+1) + x + 3(−2) = 0, so x = +5. Write the sign first (+5); 5+ would be an ion charge.
Why does first ionization energy dip from group 2 to 13 and from group 15 to 16?
2 → 13: the electron removed is in a p sublevel, higher in energy than s. 15 → 16: the electron removed is paired, and repulsion raises its energy. (HL only)
Typical transition element properties, and why zinc is excluded
Variable oxidation states, high melting points, magnetic and catalytic properties, coloured compounds, complex ions. Caused by an incomplete d-sublevel; Zn is 3d¹⁰ in the atom and in Zn²⁺. (HL only)
Why are transition element complexes coloured?
Ligands split the d orbitals into two sets; an electron absorbs visible light matching the gap and is promoted. The colour seen is the complementary colour. (HL only)

3.2 Functional groups: Classification of organic compounds

Homologous series
Same functional group and general formula; successive members differ by CH₂; similar chemistry and a gradual trend in physical properties.
Effect of branching on boiling point
Branching lowers the boiling point: less surface contact, weaker London forces.
Effect of the functional group on boiling point
For similar numbers of electrons, hydrogen bonding (–OH, –COOH) > dipole–dipole (C=O, C–X) > London forces only (alkanes).
Name ClCH₂CH₂CH₂CH(CH₃)₂ and CH₂=CHCOCH₂CH₃
1-chloro-4-methylpentane (lowest locants {1,4}). Pent-1-en-3-one (C=O is C3 either way, so the C=C decides).
Alcohol vs amine classification (primary, secondary, tertiary)
Count around the carbon vs around the nitrogen. So (CH₃)₃CNH₂ is a primary amine.
Isomer vs homologue
Isomers share a molecular formula; homologues differ by CH₂.
When does a compound show cis-trans isomerism?
When rotation is restricted (a C=C, or a C₃ or C₄ ring) and each of the two carbons carries two different groups. (HL only)
Chiral carbon, enantiomers and a racemic mixture
A chiral carbon has four different groups. Enantiomers are non-superimposable mirror images that rotate plane-polarized light by equal angles in opposite directions. A racemic mixture has equal amounts: no net rotation. (HL only)
IR: wavenumbers for C=O, alcohol O–H and carboxylic acid O–H
C=O: 1700–1750 cm⁻¹. Alcohol O–H: broad, 3200–3600 cm⁻¹. Acid O–H: very broad, 2500–3000 cm⁻¹. (HL only)
Which vibrations are IR active?
Only those that change the dipole moment. N₂ and O₂ stretches and the CO₂ symmetric stretch are not; the CO₂ asymmetric stretch and bend are. (HL only)
¹H NMR: what the number of signals, integration and splitting tell you
Signals: number of hydrogen environments. Integration: ratio of H in each. Splitting: n H on adjacent carbons give n + 1 peaks (ethyl: quartet + triplet). (HL only)
Mass spectra of butan-1-ol and butan-2-ol (both M = 74): what distinguishes them?
A strong peak at m/z 31 (CH₂OH⁺) points to OH on the end carbon: butan-1-ol. A strong peak at 45 (CH₃CHOH⁺) points to OH on carbon 2: butan-2-ol. (HL only)

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