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CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES CHAPTER RELEVANCE OVERVIEW Why this chapter matters for JEE Appeared in almost every shift for 2 straight years Frequently asked trends: atomic size, ionization energy, electronegativity, periodic law High accuracy + low conceptual load = Perfect for quick scoring Covers basics that repeat in Coordination Compounds, Chemical Bonding, and p-block. FLOW OF TOPICS HISTORY MODERN PERIODIC LAW MODERN PERIODIC TABLE PERIODICITY AND PERIODIC PROPERTIES Dobereiner's TRIADS Newlands' Law of Octaves Mendeleev's Periodic Table Based on Atomic Number ($Z$) Discovered by Moseley Overcomes anomalies of Mendeleev's Tables Periods (Horizontal rows): 1 to 7 Groups (Vertical columns): 1 to 18 Division into Blocks: s-block: Groups 1, 2 p-block: Groups 13-18 d-block: Transition metals f-block: Lanthanides, Actinides Due to repetition of similar outer shell configurations Properties show trends across a period and down a group Atomic Radius ($\downarrow$ group, $\rightarrow$ period) Ionization Enthalpy Electron Gain Enthalpy Electronegativity Valency Metallic/Non-metallic Character CORE CONCEPTS EXPLAINED MODERN PERIODIC LAW AND THE PRESENT FORM OF THE PERIODIC TABLE Henry Moseley: English physicist 1913 mein unhone elements ke X-ray spectra study kiye Inki research ne Modern Periodic Law ka base banaya Kya observe kiya Moseley ne? Jab unhone elements ke characteristic X-ray frequencies ko plot kiya against atomic number ($Z$) toh straight line mila Lekin jab ye hi plot atomic mass ke saath kiya gaya, toh koi regular pattern nahi aaya ❌ $\sqrt{\nu}$ $Z$ Matlab kya hua is observation ka? ✓ Atomic number ($Z$) – i.e., proton number – is the true identity of an element, na ki atomic mass, jaise Mendeleev soch rahe the. Number of Elements in a Period Period Number Number of Elements Reason 1st Period 2 elements 1s orbital 2nd Period 8 elements $2s + 2p$ orbitals $= 2 + 6 = 8$ 3rd Period 8 elements $3s + 3p = 8$ electrons 4th Period 18 elements $4s + 3d + 4p = 2 + 10 + 6 = 18$ 5th Period 18 elements $5s + 4d + 5p = 18$ 6th Period 32 elements $6s + 4f + 5d + 6p = 2 + 14 + 10 + 6 = 32$ 7th Period 32 elements Same as 6th includes actinides IUPAC NOMENCLATURE FOR ELEMENTS Why needed? Jab new elements discover hote hain, unke liye IUPAC ne ek temporary systematic name and symbol assign karta hai, based on atomic number. How does the system work? Har digit of the atomic number is replaced by a Latin/Greek root. Digit-to-Root Mapping Digit 0 1 2 3 4 5 6 7 8 9 Root nil un bi tri quad pent hex sept oct enn RULES FOR NAMING Roots are combined in order of digits in the atomic number. Suffix "-ium" is added at the end. If "bi" or "tri" is followed by "ium", remove the extra 'i'. Element symbol: first letter of each root, capitalize first only. Examples Element 113: Digits = 1-1-3 $\rightarrow$ un-un-tri $\rightarrow$ ununtrium Symbol = Uut Element 118: Digits = 1-1-8 $\rightarrow$ un-un-oct $\rightarrow$ ununoctium Symbol = Uuo Element 120: Digits = 1-2-0 $\rightarrow$ un-bi-nil $\rightarrow$ unbinilium Symbol = Ubn MNEMONICS FOR LEARNING ELEMENTS OF ATOMIC NUMBER > 100 My New Little Rabbit Does Some Big Help My Dear Radiant Cats, Never Find More Lovely Toys Outside. My = Md (Mendelevium - 101) New = No (Nobelium - 102) Little = Lr (Lawrencium - 103) Rabbit = Rf (Rutherfordium - 104) Does = Db (Dubnium - 105) Some = Sg (Seaborgium - 106) Big = Bh (Bohrium - 107) Help = Hs (Hassium - 108) My = Mt (Meitnerium - 109) Dear = Ds (Darmstadtium - 110) Radiant = Rg (Roentgenium - 111) Cats = Cn (Copernicium - 112) Never = Nh (Nihonium - 113) Find = Fl (Flerovium - 114) More = Mc (Moscovium - 115) Lovely = Lv (Livermorium - 116) Toys = Ts (Tennessine - 117) Outside = Og (Oganesson - 118) ELECTRONIC CONFIGURATIONS OF ELEMENTS AND THE PERIODIC TABLE Key Points to Remember (a) Electronic Configurations in Periods: The period indicates the value of $n$ for the outermost or valence shell. Period $n$ (shell) Orbitals Being Filled Element Yaad-Shakti ka Dose: 1st $n=1$ 1s 2 Sirf 1s orbital $\rightarrow$ H & He 2nd $n=2$ 2s 2p 8 2s, 2p = total 4 orbitals ($\times 2$ e$^-$) 3rd $n=3$ 3s 3p 8 3d aata hai par pehle 4s fill hota hai 4th $n=4$ 4s $\rightarrow$ 3d $\rightarrow$ 4p 18 3d transition start from Sc to Zn 5th $n=5$ 5s $\rightarrow$ 4d $\rightarrow$ 5p 18 4d transition: Y ($Z=39$) to Cd 6th $n=6$ 6s $\rightarrow$ 4f $\rightarrow$ 5d $\rightarrow$ 6p 32 Lanthanoids (4f): Ce to Lu ($Z=58-71$) 7th $n=7$ 7s $\rightarrow$ 5f $\rightarrow$ 6d $\rightarrow$ 7p 32 Actinoids (5f): Th to Lr + Man-made Conceptual Takeaway Orbitals available per shell $= n^2$ But we count only the orbitals actually filled in that period. Each orbital holds 2 electrons, so number of elements $= 2 \times$ (number of orbitals filled). Extra elements in 4th, 5th, 6th, and 7th periods because of d and f orbital inclusion. Key Idea Elements in same group (vertical column) $\rightarrow$ same number of valence electrons $\rightarrow$ similar properties That's kyunki unka valence shell electronic configuration hota hai same type ka! We can classify the elements into four blocks viz., s-block, p-block, d-block and f-block The s-Block Elements Groups Involved: Groups Name Outer Electronic Configuration 1 Alkali Metals $ns^1$ 2 Alkaline Earth Metals $ns^2$ Feature Explanation Configuration $ns^1$ (Group 1) and $ns^2$ (Group 2) Ionization Enthalpy Bahut low hoti hai $\rightarrow$ Electron easily chala jaata hai + Ions Formed Group 1 $\rightarrow M^+$ (e.g., Na$^+$) Group 2 $\rightarrow M^{2+}$ (e.g., Ca$^{2+}$) Reactivity Trend Neeche jaane par reactivity badhti hai Metallic Character Neeche jaane par metallic nature bhi badhta hai Occurrence Bahut reactive hain $\rightarrow$ Nature mein free/pure form mein nhi milta Bond Nature Mostly ionic, except Li & Be – inke compounds covalent nature ke hote hai The p-Block Elements Feature Explanation Belongs to The p-block includes elements from Group 13 to Group 18 of the periodic table. General Config The general outer electronic configuration of p-block elements ranges from $ns^2np^1$ to $ns^2np^6$ End of Period Each period ends with a noble gas (Group 18) that has a completely filled valence shell: $ns^2np^6$ Noble Gas Reactivity Noble gases are chemically inert due to their completely filled valence orbitals, making them very stable. Electron Gain Enthalpy Elements in Group 16 (Chalcogens) and Group 17 (Halogens) have highly negative electron gain enthalpies , making them highly reactive. Metallic Nature Trend Across a period (left to right): Non-metallic character increases. Down a group: Metallic Character increases. The d-Block Elements Key Properties of d-Block Elements Property Details All are metals No non-metals in d-block Coloured ions Due to unpaired d-electrons and d–d transitions Variable oxidation states Can lose different numbers of d and s electrons Paramagnetism Caused by presence of unpaired electrons Catalytic activity Many act as catalysts (e.g., Fe in Haber process, V$_2$O$_5$ in contact process) Special Note: Zn, Cd, Hg Their configuration: $(n-1)d^{10} ns^2$ These are not considered typical transition elements because: They do not show variable oxidation states Why Called Transition Elements? Because they form a "transition" Between highly reactive s-block metals and p-block elements They gradually change metallic properties across the block. The f-Block Elements Key Characteristics Feature Details All are metals Both lanthanoids and actinoids are metallic in nature. Inner Transition Elements So called because their f-orbitals are being filled, and they're "inside" the transition series. Similar properties in series Lanthanoids show very similar chemical behavior; actinoids too to some extent. Variable oxidation states Especially in actinoids, where multiple oxidation states are possible. Radioactivity All actinoids are radioactive. Synthetic elements Many actinoids (especially after uranium) are man-made and exist only in trace amounts. Transuranium Elements Elements with atomic number $> 92$ (Uranium) are called transuranium elements. Location in Periodic Table Placed separately at the bottom of the periodic table. Includes two series: Lanthanoids: Cerium (Ce, $Z=58$) to Lutetium (Lu, $Z=71$) Actinoids: Thorium (Th, $Z=90$) to Lawrencium (Lr, $Z=103$) Electronic Configuration General configuration: $(n-2)f^{1-14} (n-1)d^{0-1} ns^2$ The last electron enters an f-orbital, which defines these as f-block elements. What is Metallic Character? Metallic character is the tendency of an atom to: Lose electrons easily (to form positive ions, i.e., cations), Show properties like malleability, ductility, lustre, high electrical & thermal conductivity. The change from metallic to non-metallic character is not abrupt. Metal Characteristics Increases Metal Characteristics Increases Direction Metallic Character Reason $\downarrow$ Down a Group Increases Atomic size increases $\rightarrow$ easier to lose electrons $\leftarrow$ Across Period (left to right) Decreases More nuclear charge $\rightarrow$ harder to lose electrons 13 14 15 16 17 18 He 2p B C N O F Ne 3p Al Si P S Cl Ar 4p Ga Ge As Se Br Kr 5p In Sn Sb Te I Xe 6p Ti Pb Bi Po At Rn 7P Nh Fl Mc Lv Ts Og Si, Ge, As, Sb, Te, Po, At - Metalloids Table Talk (Periodic Style!) Q. Arrange in increasing order of metallic character: Si, Be, Mg, Na, P TRENDS IN PHYSICAL PROPERTIES ATOMIC RADIUS Atomic Radius - Atom ka Size! Yeh depend karta hai ki element metal hai ya non-metal. Non-Metals ke liye: Covalent Radius Jab do non-metal atoms ek single covalent bond se jude hote hain, to unke nuclei ke beech ki doori ka aadha hissa Covalent Radius kehlata hai. Example: Cl$_2$ molecule mein. Atomic size = $\frac{1}{2} \times$ Cl–Cl bond length Yaani dono chlorine ke nucleus ke beech jitni doori hai, uska aadha hi ek Cl atom ka size hota hai. Metals ke liye: Metallic Radius Metals mein atoms closely packed hote hain metallic crystal lattice mein. Yahaan do paas-paas ke atoms ke nucleus ke beech ki doori ka aadha hota hai Metallic Radius. Example: Solid sodium (Na) mein. Atomic size = $\frac{1}{2} \times$ Na–Na distance in metal lattice. Li Be B C N O F Ne Li Na K Rb Cs F Cl Br