Course Topics

Periodic Table Fundamentals

Modern Periodic Law (Moseley): “The physical and chemical properties of elements are the periodic function of their atomic numbers.”

Periodicity: The repetition of properties after regular intervals is called periodicity.

Term Definition
Periodic Table Elements arranged in order of increasing atomic number
Group Number Number of electrons in outermost shell (valence electrons)
Period Number Number of shells of electrons
Valence Electron Electron in outermost shell
Metals Elements with IA-IIIA valence electrons except boron
Non-metals Elements with IVA-VIIA valence electrons
Inert gases Elements with full outermost-shell of group VIII-A
Memory Tip

Modern periodic law: Properties depend on atomic number, not atomic weight!

Periodic Trends in Physical Properties

Property Trend in a Period (left to right) Trend in a Group (down the group) Factors
Atomic Radius Decreases Increases Nuclear charge, number of shells
Ionic Radius Decreases for iso-electronic ions Increases for similar charged ions Nuclear charge, number of shells
Ionization Energy Increases Decreases Nuclear charge, atomic size, shielding effect
Electron Affinity Increases Decreases Size of atom, nuclear charge, vacancies in valence shell
Electronegativity Increases Decreases Size of atom, nuclear charge
Metallic Character Decreases Increases Atomic size, nuclear charge
CRITICAL CONCEPT: The most electronegative element in the periodic table is fluorine (4.00 on Pauling scale). Metallic character increases down the group and decreases across a period.
Memory Tip

Across a period: Think “tightening” (atomic radius decreases, ionization energy increases). Down a group: Think “loosening” (atomic radius increases, ionization energy decreases).

s-Block Elements

Definition: The elements in which s-orbital is under the process of filling or has filled are called s-block elements.

  • Outer electronic configuration: ns¹⁻²
  • Groups included: IA (alkali metals) and IIA (alkaline earth metals)
  • s-Block elements consist of only metals except hydrogen
  • Highly reactive metals with low ionization energies
  • Form ionic compounds with non-metals

Group IA (Alkali Metals)

  • Li, Na, K, Rb, Cs, Fr
  • ns¹ configuration
  • +1 oxidation state
  • Highly reactive with water
  • Soft, low density metals
  • Strong reducing agents

Group IIA (Alkaline Earth Metals)

  • Be, Mg, Ca, Sr, Ba, Ra
  • ns² configuration
  • +2 oxidation state
  • Less reactive than alkali metals
  • Harder, higher melting points
  • Form basic oxides
Memory Tip

s-block = Soft metals (mostly), Shiny, Strongly reactive!

Group IA: Alkali Metals

Elements: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), Francium (Fr)

Property Trend (Li → Cs) Reason
Atomic Radius Increases Addition of extra electron shells
Ionization Energy Decreases Increased atomic size, shielding effect
Melting Point Decreases Weakening metallic bonds due to larger atomic size
Reactivity Increases Decreasing ionization energy, easier electron loss
Density Increases (except K) Increasing atomic mass outweighs increasing atomic size
CRITICAL CONCEPT – Anomalous Behavior of Lithium:
  • Lithium shows differences from other alkali metals due to its small size
  • Forms normal oxide (Li₂O) when burned in oxygen (others form peroxides or superoxides)
  • Lithium carbonate decomposes on heating (others are stable)
  • Lithium reacts with nitrogen to form Li₃N (others don’t react with nitrogen)
  • Lithium salts are less soluble in water than other alkali metal salts
Memory Tip

Alkali metal reactivity: Little Naughty Kids Rub Cats Fiercely (increasing reactivity).

Reactions of Alkali Metals with Water

Alkali metals react vigorously with water to form metal hydroxides and hydrogen gas:

2M + 2H₂O → 2MOH + H₂↑
  • The reaction is highly exothermic
  • Small pieces of Li, Na, and K float on water
  • The heat produced can ignite the hydrogen gas
  • Reactivity increases down the group: Li (slow), Na (vigorous), K (very vigorous), Rb/Cs (explosive)
  • K, Rb, and Cs react even with ice at -100°C
  • Alkali metals are stored in kerosene or paraffin oil to prevent reaction with air/moisture
CRITICAL CONCEPT: The increasing reactivity down the group is due to decreasing ionization energy. As atomic size increases, the outermost electron is less strongly held and more easily lost.
Memory Tip

Alkali metal + Water = Metal hydroxide + Hydrogen gas + Heat (so much heat it can ignite the hydrogen!).

Reactions of Alkali Metals with Oxygen

Alkali metals react with oxygen to form different types of oxides:

Metal Oxide Formed Formula Type
Lithium Lithium monoxide Li₂O Normal oxide
Sodium Sodium peroxide Na₂O₂ Peroxide
Potassium Potassium superoxide KO₂ Superoxide
Rubidium Rubidium superoxide RbO₂ Superoxide
Cesium Cesium superoxide CsO₂ Superoxide
CRITICAL CONCEPT: The tendency to form peroxides and superoxides increases down the group due to increasing size of metal ions. Larger ions stabilize larger anions (O₂²⁻ and O₂⁻) better due to lower lattice energy requirements.
Memory Tip

Alkali metals + Oxygen: Li makes normal oxide, Na makes peroxide, K/Rb/Cs make superoxides!

Flame Tests for Alkali Metals

Flame test is an analytical procedure used to detect the presence of certain metal ions based on each element’s characteristic emission spectrum.

Element Flame Color Element Flame Color
Lithium (Li) Crimson red Calcium (Ca) Brick-red
Sodium (Na) Golden yellow Strontium (Sr) Crimson red
Potassium (K) Violet Barium (Ba) Pale green
Rubidium (Rb) Reddish-violet Copper (Cu) Blue-green
Cesium (Cs) Blue Lead (Pb) Greyish-white
CRITICAL CONCEPT – Origin of Flame Colors:

The loosely held outer electron (ns¹ electron for alkali metals) can be easily excited to higher energy levels by heat energy. When the excited electron falls back to its ground state, it emits energy in the form of visible light. Different elements emit different wavelengths (colors) due to different energy level differences.

Memory Tip

Flame colors: Like Nature’s Kaleidoscope – Lithium (red), Sodium (yellow), Potassium (violet)!

Group IIA: Alkaline Earth Metals

Elements: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra)

Property Trend (Be → Ra) Reason
Atomic Radius Increases Addition of extra electron shells
Ionization Energy Decreases Increased atomic size, shielding effect
Melting Point No regular trend Complex crystal structures
Reactivity Increases Decreasing ionization energy
Density Increases Increasing atomic mass
CRITICAL CONCEPT – Anomalous Behavior of Beryllium:
  • Beryllium is amphoteric (forms salts with both acids and bases)
  • BeO is amphoteric, while other alkaline earth metal oxides are basic
  • Beryllium chloride is covalent, while others are ionic
  • Beryllium does not react with water or steam even at red heat
  • Beryllium does not impart color to flame
  • Beryllium compounds are toxic
Memory Tip

Alkaline earth metals: Be More Careful Studying Barium Reactions (increasing reactivity).

Reactions of Alkaline Earth Metals with Water

Reactivity with water increases down Group IIA:

M + 2H₂O → M(OH)₂ + H₂↑
Metal Reaction with Water Observations
Beryllium No reaction Even at red hot temperature with steam
Magnesium Very slow with cold water, reacts with steam Mg + H₂O(steam) → MgO + H₂ (white magnesium oxide formed)
Calcium Fairly vigorous with cold water Forms white precipitate of Ca(OH)₂, bubbles of H₂ gas
Strontium Vigorous reaction Similar to lithium in reactivity
Barium Very vigorous reaction Similar to sodium in reactivity
CRITICAL CONCEPT: The increasing reactivity down the group is due to decreasing ionization energy and increasing electropositive character. However, alkaline earth metals are less reactive than corresponding alkali metals due to higher ionization energies and stronger metallic bonds.
Memory Tip

Alkaline earth metals + Water: Be careful – starts with no reaction, ends with vigorous reaction!

Reactions of Alkaline Earth Metals with Oxygen & Nitrogen

With Oxygen: Alkaline earth metals burn in air to form normal oxides (MO):

2M + O₂ → 2MO
  • All form normal oxides of MO type when heated in O₂
  • BeO and MgO are insoluble in water; CaO, SrO, BaO react with water to give soluble hydroxides
  • BeO is amphoteric; others are basic with basicity increasing down the group
  • Heavier metals (Ca, Sr, Ba) form peroxides (MO₂) on heating normal oxides with O₂

With Nitrogen: All alkaline earth metals burn in nitrogen to form nitrides:

3M + N₂ → M₃N₂
  • Nitrides react with water to liberate ammonia: M₃N₂ + 6H₂O → 2NH₃ + 3M(OH)₂
  • Be₃N₂ is volatile while other nitrides are not
Memory Tip

Alkaline earth metals: Burn in air → Oxide (MO), Burn in nitrogen → Nitride (M₃N₂)!

Group IIIA Elements (Aluminum)

Aluminum (Al) – The most important element of Group IIIA:

Reaction Conditions Product Special Note
With Air Room temperature Thin Al₂O₃ coating Protective layer prevents further corrosion
With Air Heated above 800°C Al₂O₃ + AlN Used in flash photography (intense white light)
With Chlorine Heated AlCl₃ Exothermic reaction
With Water Room temperature Al(OH)₃ + H₂ Very slow due to protective oxide layer
CRITICAL CONCEPT: Aluminum is corrosion-resistant due to the formation of a thin, continuous, and impervious layer of aluminum oxide (Al₂O₃) when exposed to air. This makes aluminum useful for construction, packaging, and transportation despite its high reactivity.
Memory Tip

Aluminum: Self-protecting metal – forms its own protective coat (Al₂O₃) to prevent further reaction!

Applications & Importance

Practical Applications of s-Block Elements:

  • Lithium: Batteries (Li-ion), alloys, mood stabilizer drugs
  • Sodium: Street lighting (vapor lamps), Na-K alloy as heat transfer medium, sodium chloride as table salt
  • Potassium: Fertilizers (KNO₃, KCl), soaps, vital for nerve function in biology
  • Magnesium: Lightweight alloys (aircraft, cars), fireworks (bright white light), chlorophyll in plants
  • Calcium: Construction (cement, plaster of Paris), bones and teeth (calcium phosphate), water treatment
  • Barium: X-ray contrast medium (barium meal), fireworks (green color), vacuum tubes
  • Aluminum: Aircraft, packaging (foil), construction, electrical transmission lines
CRITICAL CONCEPT: Understanding periodic trends helps predict chemical behavior, design new materials, and explain biological functions. The s-block elements are essential for life (Na⁺, K⁺, Ca²⁺, Mg²⁺ ions) and modern technology (Li batteries, Al alloys).
Memory Tip

From batteries (Li) to bones (Ca) to airplanes (Al, Mg) – s-block elements are everywhere in modern life!