Cheat Sheet: Classification of Elements and Periodicity in Properties | Chemistry for JEE Main & Advanced PDF Download

 Page 1


Classification of Elements & Periodicity in 
Properties 
Why Classify Elements 
Organize elements, predict properties, discover new elements, standardize communication, aid 
education. 
Genesis of Periodic Classification 
Dobereiner’s Triads 
? Groups of three; middle atomic mass ˜ mean of others  
(e.g., Li:7, Na:23, K:39; mean = (7 + 39)/2 = 23). 
? Limitations: Only 5 triads, new/known elements didn’t fit. 
Newland’s Octaves 
? Every 8th element is similar (e.g., H, F, Cl). 
? Limitations: Valid up to Ca, dissimilar elements grouped, no room for noble gases. 
Lothar Meyer’s Curve 
? Atomic volume vs. atomic mass; periodic properties (e.g., peaks at alkali metals). 
? Limitations: Less predictive, no empirical basis. 
Mendeleev’s Periodic Table 
? Arranged by increasing atomic weight, similar properties in columns. 
? Periodic Law: Properties are periodic functions of atomic weights. 
Page 2


Classification of Elements & Periodicity in 
Properties 
Why Classify Elements 
Organize elements, predict properties, discover new elements, standardize communication, aid 
education. 
Genesis of Periodic Classification 
Dobereiner’s Triads 
? Groups of three; middle atomic mass ˜ mean of others  
(e.g., Li:7, Na:23, K:39; mean = (7 + 39)/2 = 23). 
? Limitations: Only 5 triads, new/known elements didn’t fit. 
Newland’s Octaves 
? Every 8th element is similar (e.g., H, F, Cl). 
? Limitations: Valid up to Ca, dissimilar elements grouped, no room for noble gases. 
Lothar Meyer’s Curve 
? Atomic volume vs. atomic mass; periodic properties (e.g., peaks at alkali metals). 
? Limitations: Less predictive, no empirical basis. 
Mendeleev’s Periodic Table 
? Arranged by increasing atomic weight, similar properties in columns. 
? Periodic Law: Properties are periodic functions of atomic weights. 
? Predicted Eka-Aluminium (Ga), Eka-Silicon (Ge), Eka-Boron (Sc). 
? Limitations: Isotopes, incorrect mass order, H position. 
Modern Periodic Table 
? Modern Periodic Law: Properties are periodic functions of atomic numbers. 
? Structure: Periods (rows, energy levels), groups (columns, similar properties). 
? Classification: Metals (left), non-metals (top-right), metalloids (diagonal). 
? Blocks: s, p, d, f (based on orbital filling). 
? Trends: Atomic radius, ionization enthalpy, electron gain enthalpy, electronegativity. 
? Special Groups: Transition metals (d-block), lanthanides/actinides (f-block). 
Nomenclature (Z > 100) 
? Rules: Numerical roots (0 = nil, 1 = un, 2 = bi, etc.) + -ium; symbol from root initials (e.g., 
Z = 120 ? unbinilium, Ubn). 
? Example: Z = 113 ? ununtrium (Uut), official: Nihonium (Nh). 
Electronic Configurations & Blocks 
Aufbau Principle 
? Electrons fill orbitals by increasing energy: 1s, 2s, 2p, 3s, 3p, 3d, etc. 
s-Block 
? Groups 1 (ns¹, alkali metals), 2 (ns², alkaline earth metals). 
? Reactive, form ionic compounds, low ionization enthalpy. 
p-Block 
? Groups 13–18 (ns²np¹ ? 6); non-metals, metalloids, noble gases (ns²np 6, low reactivity). 
Page 3


Classification of Elements & Periodicity in 
Properties 
Why Classify Elements 
Organize elements, predict properties, discover new elements, standardize communication, aid 
education. 
Genesis of Periodic Classification 
Dobereiner’s Triads 
? Groups of three; middle atomic mass ˜ mean of others  
(e.g., Li:7, Na:23, K:39; mean = (7 + 39)/2 = 23). 
? Limitations: Only 5 triads, new/known elements didn’t fit. 
Newland’s Octaves 
? Every 8th element is similar (e.g., H, F, Cl). 
? Limitations: Valid up to Ca, dissimilar elements grouped, no room for noble gases. 
Lothar Meyer’s Curve 
? Atomic volume vs. atomic mass; periodic properties (e.g., peaks at alkali metals). 
? Limitations: Less predictive, no empirical basis. 
Mendeleev’s Periodic Table 
? Arranged by increasing atomic weight, similar properties in columns. 
? Periodic Law: Properties are periodic functions of atomic weights. 
? Predicted Eka-Aluminium (Ga), Eka-Silicon (Ge), Eka-Boron (Sc). 
? Limitations: Isotopes, incorrect mass order, H position. 
Modern Periodic Table 
? Modern Periodic Law: Properties are periodic functions of atomic numbers. 
? Structure: Periods (rows, energy levels), groups (columns, similar properties). 
? Classification: Metals (left), non-metals (top-right), metalloids (diagonal). 
? Blocks: s, p, d, f (based on orbital filling). 
? Trends: Atomic radius, ionization enthalpy, electron gain enthalpy, electronegativity. 
? Special Groups: Transition metals (d-block), lanthanides/actinides (f-block). 
Nomenclature (Z > 100) 
? Rules: Numerical roots (0 = nil, 1 = un, 2 = bi, etc.) + -ium; symbol from root initials (e.g., 
Z = 120 ? unbinilium, Ubn). 
? Example: Z = 113 ? ununtrium (Uut), official: Nihonium (Nh). 
Electronic Configurations & Blocks 
Aufbau Principle 
? Electrons fill orbitals by increasing energy: 1s, 2s, 2p, 3s, 3p, 3d, etc. 
s-Block 
? Groups 1 (ns¹, alkali metals), 2 (ns², alkaline earth metals). 
? Reactive, form ionic compounds, low ionization enthalpy. 
p-Block 
? Groups 13–18 (ns²np¹ ? 6); non-metals, metalloids, noble gases (ns²np 6, low reactivity). 
d-Block 
? Groups 3–12 ((n-1)d¹ ?¹ °ns ° ?²); transition metals, variable oxidation states, colored ions. 
? Exception: Zn, Cd, Hg ((n-1)d 1 0ns²) not typical transition metals. 
f-Block Elements 
? Lanthanides (4f, Ce–Lu), actinides (5f, Th–Lr); inner transition, radioactive actinides. 
Metals, Non-Metals, Metalloids 
? Metals: Conductive, malleable, high melting/boiling points (left). 
? Non-Metals: Poor conductors, brittle, low melting/boiling points (top-right). 
? Metalloids: Intermediate properties, semiconductors (B, Si, Ge, As, Sb, Te, Po). 
Periodic Trends in Physical Properties 
Atomic Radius 
? Decreases across period (? nuclear charge), increases down group (? shells). 
? Transition metals: Slight ? (Sc–Mn), constant (Fe–Ni), slight ? (Cu–Zn). 
? Lanthanide contraction: ? radius in 4f series. 
Ionic Radius 
? Cations: Smaller than parent (? e ?). Anions: Larger (? e ? repulsion). 
? Isoelectronic species: Smaller with higher nuclear charge. 
Ionization Enthalpy (IE) 
? ? across period (? radius, ? charge), ? down group (? radius). 
? Factors: Size, nuclear charge, penetration (s>p>d>f), shielding, half-filled orbitals. 
Page 4


Classification of Elements & Periodicity in 
Properties 
Why Classify Elements 
Organize elements, predict properties, discover new elements, standardize communication, aid 
education. 
Genesis of Periodic Classification 
Dobereiner’s Triads 
? Groups of three; middle atomic mass ˜ mean of others  
(e.g., Li:7, Na:23, K:39; mean = (7 + 39)/2 = 23). 
? Limitations: Only 5 triads, new/known elements didn’t fit. 
Newland’s Octaves 
? Every 8th element is similar (e.g., H, F, Cl). 
? Limitations: Valid up to Ca, dissimilar elements grouped, no room for noble gases. 
Lothar Meyer’s Curve 
? Atomic volume vs. atomic mass; periodic properties (e.g., peaks at alkali metals). 
? Limitations: Less predictive, no empirical basis. 
Mendeleev’s Periodic Table 
? Arranged by increasing atomic weight, similar properties in columns. 
? Periodic Law: Properties are periodic functions of atomic weights. 
? Predicted Eka-Aluminium (Ga), Eka-Silicon (Ge), Eka-Boron (Sc). 
? Limitations: Isotopes, incorrect mass order, H position. 
Modern Periodic Table 
? Modern Periodic Law: Properties are periodic functions of atomic numbers. 
? Structure: Periods (rows, energy levels), groups (columns, similar properties). 
? Classification: Metals (left), non-metals (top-right), metalloids (diagonal). 
? Blocks: s, p, d, f (based on orbital filling). 
? Trends: Atomic radius, ionization enthalpy, electron gain enthalpy, electronegativity. 
? Special Groups: Transition metals (d-block), lanthanides/actinides (f-block). 
Nomenclature (Z > 100) 
? Rules: Numerical roots (0 = nil, 1 = un, 2 = bi, etc.) + -ium; symbol from root initials (e.g., 
Z = 120 ? unbinilium, Ubn). 
? Example: Z = 113 ? ununtrium (Uut), official: Nihonium (Nh). 
Electronic Configurations & Blocks 
Aufbau Principle 
? Electrons fill orbitals by increasing energy: 1s, 2s, 2p, 3s, 3p, 3d, etc. 
s-Block 
? Groups 1 (ns¹, alkali metals), 2 (ns², alkaline earth metals). 
? Reactive, form ionic compounds, low ionization enthalpy. 
p-Block 
? Groups 13–18 (ns²np¹ ? 6); non-metals, metalloids, noble gases (ns²np 6, low reactivity). 
d-Block 
? Groups 3–12 ((n-1)d¹ ?¹ °ns ° ?²); transition metals, variable oxidation states, colored ions. 
? Exception: Zn, Cd, Hg ((n-1)d 1 0ns²) not typical transition metals. 
f-Block Elements 
? Lanthanides (4f, Ce–Lu), actinides (5f, Th–Lr); inner transition, radioactive actinides. 
Metals, Non-Metals, Metalloids 
? Metals: Conductive, malleable, high melting/boiling points (left). 
? Non-Metals: Poor conductors, brittle, low melting/boiling points (top-right). 
? Metalloids: Intermediate properties, semiconductors (B, Si, Ge, As, Sb, Te, Po). 
Periodic Trends in Physical Properties 
Atomic Radius 
? Decreases across period (? nuclear charge), increases down group (? shells). 
? Transition metals: Slight ? (Sc–Mn), constant (Fe–Ni), slight ? (Cu–Zn). 
? Lanthanide contraction: ? radius in 4f series. 
Ionic Radius 
? Cations: Smaller than parent (? e ?). Anions: Larger (? e ? repulsion). 
? Isoelectronic species: Smaller with higher nuclear charge. 
Ionization Enthalpy (IE) 
? ? across period (? radius, ? charge), ? down group (? radius). 
? Factors: Size, nuclear charge, penetration (s>p>d>f), shielding, half-filled orbitals. 
Electron Gain Enthalpy (EGH) 
? More negative across periods (except noble gases), less negative down group. 
? Factors: Size, nuclear charge, shielding, half-filled orbitals. 
Electronegativity 
? ? across period, ? down group. 
? Scales: Pauling (F=4), Mulliken, Allred-Rochow. 
? Factors: Radius, nuclear charge, oxidation state, hybridization (sp > sp² > sp³). 
Periodic Trends in Chemical Properties 
Valence/Oxidation States 
? Period: ? to 4, then ? to 0. Group: Constant valence; transition elements vary. 
? Rule: Valence = e ? (=4) or 8–e ? (>4). 
Anomalous Properties (Second Period) 
? Li–F: Small size, high electronegativity, covalent compounds, diagonal relationships 
(e.g., Li–Mg). 
Chemical Reactivity 
? High at period extremes: Left (lose e ?), right (gain e ?). 
? Oxides: Basic (left, e.g., Na 2O), acidic (right, e.g., SO 3), amphoteric/neutral (center, e.g., 
Al 2O 3). 
? Metallic character: ? across period, ? down group. 
Periodic Trends Table 
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Classification of Elements & Periodicity in 
Properties 
Why Classify Elements 
Organize elements, predict properties, discover new elements, standardize communication, aid 
education. 
Genesis of Periodic Classification 
Dobereiner’s Triads 
? Groups of three; middle atomic mass ˜ mean of others  
(e.g., Li:7, Na:23, K:39; mean = (7 + 39)/2 = 23). 
? Limitations: Only 5 triads, new/known elements didn’t fit. 
Newland’s Octaves 
? Every 8th element is similar (e.g., H, F, Cl). 
? Limitations: Valid up to Ca, dissimilar elements grouped, no room for noble gases. 
Lothar Meyer’s Curve 
? Atomic volume vs. atomic mass; periodic properties (e.g., peaks at alkali metals). 
? Limitations: Less predictive, no empirical basis. 
Mendeleev’s Periodic Table 
? Arranged by increasing atomic weight, similar properties in columns. 
? Periodic Law: Properties are periodic functions of atomic weights. 
? Predicted Eka-Aluminium (Ga), Eka-Silicon (Ge), Eka-Boron (Sc). 
? Limitations: Isotopes, incorrect mass order, H position. 
Modern Periodic Table 
? Modern Periodic Law: Properties are periodic functions of atomic numbers. 
? Structure: Periods (rows, energy levels), groups (columns, similar properties). 
? Classification: Metals (left), non-metals (top-right), metalloids (diagonal). 
? Blocks: s, p, d, f (based on orbital filling). 
? Trends: Atomic radius, ionization enthalpy, electron gain enthalpy, electronegativity. 
? Special Groups: Transition metals (d-block), lanthanides/actinides (f-block). 
Nomenclature (Z > 100) 
? Rules: Numerical roots (0 = nil, 1 = un, 2 = bi, etc.) + -ium; symbol from root initials (e.g., 
Z = 120 ? unbinilium, Ubn). 
? Example: Z = 113 ? ununtrium (Uut), official: Nihonium (Nh). 
Electronic Configurations & Blocks 
Aufbau Principle 
? Electrons fill orbitals by increasing energy: 1s, 2s, 2p, 3s, 3p, 3d, etc. 
s-Block 
? Groups 1 (ns¹, alkali metals), 2 (ns², alkaline earth metals). 
? Reactive, form ionic compounds, low ionization enthalpy. 
p-Block 
? Groups 13–18 (ns²np¹ ? 6); non-metals, metalloids, noble gases (ns²np 6, low reactivity). 
d-Block 
? Groups 3–12 ((n-1)d¹ ?¹ °ns ° ?²); transition metals, variable oxidation states, colored ions. 
? Exception: Zn, Cd, Hg ((n-1)d 1 0ns²) not typical transition metals. 
f-Block Elements 
? Lanthanides (4f, Ce–Lu), actinides (5f, Th–Lr); inner transition, radioactive actinides. 
Metals, Non-Metals, Metalloids 
? Metals: Conductive, malleable, high melting/boiling points (left). 
? Non-Metals: Poor conductors, brittle, low melting/boiling points (top-right). 
? Metalloids: Intermediate properties, semiconductors (B, Si, Ge, As, Sb, Te, Po). 
Periodic Trends in Physical Properties 
Atomic Radius 
? Decreases across period (? nuclear charge), increases down group (? shells). 
? Transition metals: Slight ? (Sc–Mn), constant (Fe–Ni), slight ? (Cu–Zn). 
? Lanthanide contraction: ? radius in 4f series. 
Ionic Radius 
? Cations: Smaller than parent (? e ?). Anions: Larger (? e ? repulsion). 
? Isoelectronic species: Smaller with higher nuclear charge. 
Ionization Enthalpy (IE) 
? ? across period (? radius, ? charge), ? down group (? radius). 
? Factors: Size, nuclear charge, penetration (s>p>d>f), shielding, half-filled orbitals. 
Electron Gain Enthalpy (EGH) 
? More negative across periods (except noble gases), less negative down group. 
? Factors: Size, nuclear charge, shielding, half-filled orbitals. 
Electronegativity 
? ? across period, ? down group. 
? Scales: Pauling (F=4), Mulliken, Allred-Rochow. 
? Factors: Radius, nuclear charge, oxidation state, hybridization (sp > sp² > sp³). 
Periodic Trends in Chemical Properties 
Valence/Oxidation States 
? Period: ? to 4, then ? to 0. Group: Constant valence; transition elements vary. 
? Rule: Valence = e ? (=4) or 8–e ? (>4). 
Anomalous Properties (Second Period) 
? Li–F: Small size, high electronegativity, covalent compounds, diagonal relationships 
(e.g., Li–Mg). 
Chemical Reactivity 
? High at period extremes: Left (lose e ?), right (gain e ?). 
? Oxides: Basic (left, e.g., Na 2O), acidic (right, e.g., SO 3), amphoteric/neutral (center, e.g., 
Al 2O 3). 
? Metallic character: ? across period, ? down group. 
Periodic Trends Table 
Property Across Period Down Group Examples 
Atomic Radius ? (? nuclear 
charge) 
? (? shells) Na > Mg; Cs > Na 
Ionic Radius ? (cations < 
anions) 
? (? shells) Na ? < Na; K ? > 
Na ? 
Ionization 
Enthalpy 
? (? radius) ? (? radius) Cl > Na; Na > K 
Electron Gain 
Enthalpy 
More negative 
(except noble 
gases) 
Less negative Cl: -349 kJ/mol; 
Br: -324 kJ/mol 
Electronegativity ? (? nuclear 
charge) 
? (? radius) F: 4.0; Cl: 3.0