Comprehensive Study Notes: Classification of Elements and Periodic Trends

Inorganic Chemistry: Weightage and Overview

• Weightage Distribution:     - 1st Year Topics:         1. Classification of Elements: $2$ questions.         2. Chemical Bonding: $2$ questions.         3. S-Block, 13th & 14th Groups: $8$ questions (combined with 2nd year group totals).     - 2nd Year Topics:         1. P-Block (15th to 18th Groups): $5$ questions.         2. D, F & Coordination Compounds: $5$ questions.
• Classification of Elements Introduction:     - Primary focus on topics: Atomic Size, Ionization Energy, Electron Gain Enthalpy, Electronegativity, Metallic & Nonmetallic character, and Nature of Oxides.     - Blocks: Periodic table divided into $s, p, d, f$.

S-Block Elements

• Group-1 (Alkali Metals):     - General valence electronic configuration: $ns^1$.     - Elements and Atomic Numbers (using Magic Numbers: 8, 8, 18, 18, 32):         - Lithium ($Li$): $Z = 3$         - Sodium ($Na$): $Z = 11$ ($3+8$)         - Potassium ($K$): $Z = 19$ ($11+8$)         - Rubidium ($Rb$): $Z = 37$ ($19+18$)         - Caesium ($Cs$): $Z = 55$ ($37+18$)         - Francium ($Fr$): $Z = 87$ ($55+32$)     - Short Trick (Mnemonic): Li So Po Ru Cs Fr.
• Group-2 (Alkaline Earth Metals):     - General valence electronic configuration: $ns^2$.     - Elements and Atomic Numbers:         - Beryllium ($Be$): $Z = 4$         - Magnesium ($Mg$): $Z = 12$         - Calcium ($Ca$): $Z = 20$         - Strontium ($Sr$): $Z = 38$         - Barium ($Ba$): $Z = 56$         - Radium ($Ra$): $Z = 88$     - Short Trick: Be Mg Ca Sr Ba Ra.

P-Block Elements (Groups 13 to 18)

• General Configuration: $ns^2 np^{1-6}$.
• Group-13 (Boron Family):     - Elements: Boron ($B$, $Z=5$), Aluminium ($Al$, $Z=13$), Gallium ($Ga$, $Z=31$), Indium ($In$, $Z=49$), Thallium ($Tl$, $Z=81$).     - New element: Nihonium ($Nh$, $Z=113$).
• Group-14 (Carbon Family):     - Elements: Carbon ($C$, $Z=6$), Silicon ($Si$, $Z=14$), Germanium ($Ge$, $Z=32$), Tin ($Sn$, $Z=50$), Lead ($Pb$, $Z=82$).     - New element: Flerovium ($Fl$, $Z=114$).
• Group-15 (Nitrogen Family/Pnictogens):     - Elements: Nitrogen ($N$, $Z=7$), Phosphorus ($P$, $Z=15$), Arsenic ($As$, $Z=33$), Antimony ($Sb$, $Z=51$), Bismuth ($Bi$, $Z=83$).     - New element: Moscovium ($Mc$, $Z=115$).
• Group-16 (Oxygen Family/Chalcogens):     - Elements: Oxygen ($O$, $Z=8$), Sulphur ($S$, $Z=16$), Selenium ($Se$, $Z=34$), Tellurium ($Te$, $Z=52$), Polonium ($Po$, $Z=84$).     - New element: Livermorium ($Lv$, $Z=116$).
• Group-17 (Halogens):     - Elements: Fluorine ($F$, $Z=9$), Chlorine ($Cl$, $Z=17$), Bromine ($Br$, $Z=35$), Iodine ($I$, $Z=53$), Astatine ($At$, $Z=85$).     - New element: Tennessine ($Ts$, $Z=117$).
• Group-18 (Noble Gases):     - Elements: Helium ($He$, $Z=2$), Neon ($Ne$, $Z=10$), Argon ($Ar$, $Z=18$), Krypton ($Kr$, $Z=36$), Xenon ($Xe$, $Z=54$), Radon ($Rn$, $Z=86$).     - New element: Oganesson ($Og$, $Z=118$).

D-Block and F-Block Elements

• D-Block Series:     - 3d-series (4th Period): Scandium ($Sc$, 21) to Zinc ($Zn$, 30).     - 4d-series (5th Period): Yttrium ($Y$, 39) to Cadmium ($Cd$, 48).     - 5d-series (6th Period): Lanthanum ($La$, 57), then Hafnium ($Hf$, 72) to Mercury ($Hg$, 80).     - 6d-series (7th Period): Actinium ($Ac$, 89), then Rutherfordium ($Rf$, 104) to Copernicium ($Cn$, 112).     - Coinage elements (G$-11): Copper ($Cu$), Silver ($Ag$), Gold ($Au$).
• F-Block Elements (Inner Transition Elements):     - 4f-series (Lanthanides): Cerium ($Ce$, 58) to Lutetium ($Lu$, 71).         - Configuration: $[Xe] 4f^{1-14} 5d^{0-1} 6s^2$.     - 5f-series (Actinides): Thorium ($Th$, 90) to Lawrencium ($Lr$, 103).         - Configuration: $[Rn] 5f^{1-14} 6d^{0-1} 7s^2$.

IUPAC Nomenclature for Elements $Z > 100$

• Digits and Roots:     - $0: nil (n)$, $1: un (u)$, $2: bi (b)$, $3: tri (t)$, $4: quad (q)$, $5: pent (p)$, $6: hex (h)$, $7: sept (s)$, $8: oct (o)$, $9: enn (e)$.
• Rules: Combine roots and end with "ium".
• Examples:     - $Z = 105$: Un ($1$) + Nil ($0$) + Pent ($5$) + ium = Unnilpentium ($unp$).     - $Z = 119$: Un ($1$) + Un ($1$) + Enn ($9$) + ium = Ununennium ($uue$).

Periodic Trends: Atomic Size

• General Trends:     - Group: Increases from Top to Bottom (Addition of new shells).     - Period: Decreases from Left to Right (Increase in effective nuclear charge).
• Types of Radii:     - Van der Waals radius (Noble gases; largest).     - Metallic radius (Metals).     - Covalent radius (Non-metals; smallest).
• Ionic Radius:     - Cationic: Radius decreases as positive charge increases ($A > A^+ > A^{2+} > A^{3+}$).     - Anionic: Radius increases as negative charge increases ($A^{3-} > A^{2-} > A^- > A$).
• Isoelectronic Species (Same number of electrons):     - Size order: $N^{3-} > O^{2-} > F^- > Ne > Na^+ > Mg^{2+} > Al^{3+}$.
• Exceptions and Specific Orders:     - Noble Gases: Have the largest radius in their period due to Van der Waals forces ($Ne > Li > Be...$).     - 3d Series: Small fluctuations; Scandium ($Sc$) is largest, Zinc ($Zn$) is larger than Nickel ($Ni$) due to full $d$ subshell electron-electron repulsion.     - Group 13: $B < Ga < Al < In < Tl$ (Gallium is smaller than Aluminium due to poor shielding by $3d$ electrons - d-block contraction).     - 4d vs 5d: Size of 4d elements is nearly equal to 5d elements due to Lanthanide Contraction ($Zr \approx Hf$, $Nb \approx Ta$).

Periodic Trends: Ionization Energy (IE)

• Definition: Minimum energy required to remove the outermost valence electron from a neutral gaseous atom.
• Process: Endothermic ($\Delta H = +ve$).
• Trends:     - Group: Decreases Top to Bottom.     - Period: Increases Left to Right.
• Successive IE: $IE_1 < IE_2 < IE_3$. Note that $IE_2$ is always much greater than $IE_1$.
• Exceptions (Based on Stability):     - Full-filled ($s^2, p^6$) and Half-filled ($p^3, d^5$) configurations are highly stable and require more energy.     - Period 2: $Li < B < Be < C < O < N < F < Ne$.         - $Be (1s^2 2s^2)$ > $B (1s^2 2s^2 2p^1)$.         - $N (2p^3)$ > $O (2p^4)$.     - Period 3: $Na < Al < Mg < Si < S < P < Cl < Ar$.
• Group 13 Exception: $B > Tl > Ga > Al > In$.

Periodic Trends: Electron Gain Enthalpy ($\Delta H_{eg}$)

• Definition: Energy change when an electron is added to a neutral gaseous atom.
• Sign Convention:     - Exothermic: Energy released ($EA = +ve, \Delta H_{eg} = -ve$). Most non-metals.     - Endothermic: Energy absorbed ($EA = -ve, \Delta H_{eg} = +ve$). Noble gases, alkaline earth metals ($Be, Mg$), and Nitrogen family ($N$).
• Trends:     - Group: Generally decreases Top to Bottom.     - Period: Increases Left to Right.
• Important Comparisons:     - Chlorine ($Cl$) has the highest (most negative) electron gain enthalpy in the periodic table ($-349\,kJ\,mol^{-1}$).     - Fluorine ($F$) has a lower value than Chlorine ($-328\,kJ\,mol^{-1}$) due to small size and high electron-electron repulsion.     - Order in Halogens: $Cl > F > Br > I$.     - Order in Oxygen Family: $S > Se > Te > Po > O$ (Oxygen is the least negative due to small size/repulsion).

Periodic Trends: Electronegativity (EN)

• Definition: Ability of an atom in a chemical bond to attract bonded electrons toward itself.
• Trends:     - Group: Decreases Top to Bottom.     - Period: Increases Left to Right.
• Mulliken Scale Formula:     - $E.N = \frac{Ionization\ Energy + Electron\ Gain\ Enthalpy}{2}$ (All units in electron volts, $eV$).
• Key Values (Pauling Scale):     - $F = 4.0$ (Highest)     - $O = 3.5$     - $N = 3.0, Cl = 3.0$     - $C = 2.5, S = 2.58, I = 2.66$     - $Cs = 0.7$ (Lowest)

Nature of Oxides and Metallic Character

• Metallic vs Non-metallic Character:     - Metallic: Increases Top to Bottom; decreases Left to Right.     - Non-metallic: Decreases Top to Bottom; increases Left to Right.
• Metalloids/Semimetals: $B, Si, Ge, As, Sb, Te, At, Po$.
• Classification of Oxides:     - Basic Oxides: Metals with low oxidation states (e.g., $Li_2O, Na_2O, MgO, BaO, CrO$).     - Acidic Oxides: Non-metals and metals in high oxidation states (e.g., $B_2O_3, CO_2, P_2O_5, SO_3, Cl_2O_7, Mn_2O_7$).     - Amphoteric Oxides: Show both acidic and basic character (e.g., $BeO, Al_2O_3, ZnO, PbO, SnO, SnO_2, Ga_2O_3$).     - Neutral Oxides: Do not react with acids or bases (e.g., $CO, NO, N_2O$).

Diagonal Relationship

• Diagonal elements in Periods 2 and 3 show similar properties due to similar size and ionic potential.
• Pairs:     1. $Li$ and $Mg$     2. $Be$ and $Al$     3. $B$ and $Si$

Questions & Discussion

• Q: Matching symbols to Group Numbers (Moscovium, Livermorium, Flerovium, Tennessine):     - $Mc$ is Group 15; $Lv$ is Group 16; $Fl$ is Group 14; $Ts$ is Group 17.
• Q: Correct order of Atomic Radii of $C, Al, S$:     - $C < S < Al$ (Carbon is top right, Aluminium is bottom left relative to $S$).
• Q: Ionization Enthalpy of Aluminium relative to $Na$ (496), $Mg$ (737), $Si$ (786):     - Due to the exception ($IE_{Al} < IE_{Mg}$), the value of Aluminium is $575\,kJ\,mol^{-1}$.
• Q: Enthalpy change for $Mg + 2F \rightarrow MgF_2$:     - Calculated by: $IE_1(Mg) + IE_2(Mg) - 2 \times EA(F)$.     - $737 + 1451 - 2(328) = 1532\,kJ\,mol^{-1}$.
• Q: Highest and Lowest Electronegativity pairing:     - Highest: Fluorine ($F$); Lowest: Francium ($Fr$).
• Q: Ratio of s-electrons to p-electrons in $K^+$ and $Cr^{3+}$:     - $K^+ (Z=19-1=18)$: configuration $1s^2 2s^2 2p^6 3s^2 3p^6$. $s=6, p=12$. Ratio $1:2$.     - $Cr^{3+} (Z=24-3=21)$: configuration $1s^2 2s^2 2p^6 3s^2 3p^6 3d^3$. $s=6, p=12$. Ratio $1:2$. Result: Same.