Periodic Table and Periodic Trends – Vocabulary Flashcards

Modern Periodic Law and Table

• Modern Periodic Law: physical & chemical properties are periodic functions of atomic number (Z).

• Long‐form table: 7 periods, 18 groups, four blocks (s, p, d, f).

• Positioning exceptions

– \text{He} chemically noble gas but electronic s-block ⇒ placed with Group 18.

– H can lose 1e^- (alkali-like) or gain 1e^- (halogen-like) ⇒ shown separately.

• Block characteristics

– s-block (ns^{1-2}): active metals, low \Delta_iH, form +1/+2 cations.

– p-block (ns^2np^{1-6}): includes halogens (highly electronegative) & chalcogens; ends each period with noble gas (ns^2np^6).

– d-block ((n-1)d^{1-10}ns^{0-2}): transition metals, variable \text{OS}, coloured ions, catalysts, paramagnetic. Zn, Cd, Hg (d^{10}) behave atypically.

– f-block ((n-2)f^{1-14}(n-1)d^{0-1}ns^2): inner-transition; 4f = lanthanoids, 5f = actinoids (radioactive, many +3–+6 states).

• Periods grow as orbitals become available: 2, 8, 8, 18, 18, 32, (32 incomplete).

Nomenclature for Z>100 (IUPAC)

• Temporary name = numerical roots + “ium”. Example Z=120 ➝ roots un-bi-nil + ium ⇒ Unbinilium, Ubn.

• Official names (after confirmation) e.g. Z=106 Seaborgium (Sg).

Periodic Trends in Physical Properties

1. Atomic & Ionic Radii

• Across period: radius ↓ (greater Z_{eff}, same n).

• Down group: radius ↑ (higher n, shielding > ↑Z).

• Cation #### 2. Ionisation Enthalpy (\Delta_iH)
• Energy to remove e⁻: always >0.

• Trends: ↑ across period, ↓ down group.

• Successive \DeltaiH: \DeltaiH_1 #### 3. Electron Gain Enthalpy (\Delta_{eg}H) & Affinity
• Process: \text{X}(g)+e^-\rightarrow \text{X}^-(g).

• Negative \Delta_{eg}H ⇒ exothermic (favourable).

• More negative across a period; less negative down a group.

• Exceptions: O, F less negative than S, Cl (e⁻–e⁻ repulsion in small 2p).

• Sample data (kJ mol^{-1}):

– Group 17: \text{F}= -328, \text{Cl}= -349, \text{Br}= -325, \text{I}= -295.

– Group 18 (positive): \text{Ne}= +116.

4. Electronegativity (Pauling)

• Qualitative pull on shared e⁻.

• Increases left→right; decreases down group.

• Inverse to metallic character.

– Period 2 values: Li 1.0 → F 4.0.

– Group 1 values: Li 1.0 ↓ Cs 0.7.

5. Metallic vs Non-metallic Character

• Metallic ↑ down group, ↓ across period.

• Borderline (zig-zag) ⇒ metalloids: Si, Ge, As, Sb, Te.

Periodic Trends in Chemical Properties

1. Valence / Oxidation State

• Representative elements: valence = no. of outer e⁻ or 8-n{outer}. – Group pattern: 1, 2, 3, 4, 3/5, 2/6, 1/7, 0. • Oxidation state depends on electronegativity context. – Examples: \text{O} is +2 in \text{OF}2 but -2 in \text{Na}_2\text{O}$.

2. Reactivity Pattern

• Extremes of a period most reactive:

– Left (alkali): low \DeltaiH ⇒ easy e⁻ loss (strong reducers). – Right (halogens): high \text{-}\Delta{eg}H ⇒ easy e⁻ gain (strong oxidisers).

• Centre of period ⇒ minimum reactivity; amphoteric behaviour.

3. Nature of Oxides

• Across period: basic → amphoteric/neutral → acidic.

– Examples period 3: \text{Na}2\text{O} (basic), \text{Al}2\text{O}3 (amphoteric), \text{SiO}2 (weak acid), \text{Cl}2\text{O}7 (strong acid).

• Demonstration (Problem 3.10):

– \text{Na}2\text{O}+\text{H}2\text{O}\rightarrow 2\text{NaOH} (blue litmus)

– \text{Cl}2\text{O}7+\text{H}2\text{O}\rightarrow 2\text{HClO}4$$ (red litmus)