Group Properties and Elements

Electronic Configuration: All group 1 elements have $ns^1$ configuration in outermost shell.

Alkali Metals: Metals of group 1 are called alkali metals because when they combine with water, they produce alkalies (bases).

Atomic Size: Increases from top to bottom in the group.

Reactivity: Group 1 metals are extremely reactive and their reactivity increases down the group due to increase in atomic size.

Physical Properties: Relatively soft metals. Melting point decreases down group (Li: 180°C, Na: 98°C, K: 39°C). Density increases down group (Li: 0.53 g/cm³, Na: 0.97 g/cm³, K: 0.86 g/cm³).

Reaction with Water:

• Lithium: Reacts steadily - $2Li + 2H_2O \to 2LiOH + H_2$
• Sodium: Reacts vigorously - $2Na + 2H_2O \to 2NaOH + H_2$
• Potassium: Reacts violently - $2K + 2H_2O \to 2KOH + H_2$

Reaction with Chlorine: $2Li + Cl_2 \to 2LiCl$; $2Na + Cl_2 \to 2NaCl$; $2K + Cl_2 \to 2KCl$

Reaction with Oxygen: $4Li + O_2 \to 2Li_2O$; $4Na + O_2 \to 2Na_2O$; $4K + O_2 \to 2K_2O$. Reaction becomes more vigorous down the group.

Definition: Group 17 elements are generally known as halogens.

Valence Electrons: All have 7 electrons in outermost shell ($ns^2np^5$ configuration).

Nature: Electronegative non-metals with strong tendency to accept one electron to become negative ion (anion).

Occurrence: Exist as diatomic molecules. Very reactive non-metals.

Physical States & Colors:

• Fluorine ($F_2$): Pale yellow gas
• Chlorine ($Cl_2$): Yellowish green gas
• Bromine ($Br_2$): Fuming red-brown liquid
• Iodine ($I_2$): Shiny grey crystals (turn dark purple vapor when warmed)

Trends: Atomic radii, melting and boiling points increase down group. Reactivity decreases down group due to increase in atomic size.

Oxidizing Nature: Halogens are oxidizing agents. Oxidizing power decreases down the group.

Displacement Reactions: More reactive halogen can displace less reactive halogen from its compound.

• $Cl_2 + 2NaBr \to 2NaCl + Br_2$
• $Cl_2 + 2NaI \to 2NaCl + I_2$
• $Br_2 + 2NaI \to 2NaBr + I_2$

Reaction with Hydrogen: Halogens react with hydrogen to give hydrogen halides: $H_2 + X_2 \to 2HX$

Hydrogen Halides: Compounds of halogens with hydrogen (HF, HCl, HBr, HI). All exist in gaseous state at ordinary temperature except HF.

Bond Length & Thermal Stability: Bond length increases down group. Thermal stability decreases down group: HF > HCl > HBr > HI.

Definition: Elements in which d or f orbitals are under the process of completion are called transition elements. Example: Iron.

Position: Elements present at center of modern periodic table, from group 3 to group 12, are called transition elements or d-block elements.

Properties: All are metals with similar properties. They are hard with higher densities. High melting and boiling points. Show variable oxidation states. Form colored compounds. Malleable and ductile.

Catalytic Role:

• Iron: Haber process for ammonia production ($N_2 + 3H_2 \rightleftharpoons 2NH_3$)
• Platinum/Vanadium pentoxide ($V_2O_5$): Contact process for sulfuric acid ($2SO_2 + O_2 \to 2SO_3$)
• Pt, Pd, Rh: Catalytic converters
• Nickel: Hydrogenation of oils to solid margarine

Definition: Elements present in group 18 of modern periodic table are called noble gases or noble elements.

Nature: All are monoatomic gases. Unreactive gases with very little chemical reactivity.

Examples: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn).

Electronic Configuration: All noble gases have 8 electrons in outermost shell (except Helium which has 2 electrons). Configuration: $ns^2np^6$ or $1s^2$ for He.

Chemical Reactivity: Very little chemical reactivity because their outermost shells are complete.

Trends: Melting and boiling points increase down the group due to increase in atomic sizes and increase in weak intermolecular forces.

Metals:

• Nature of bonding: Form metallic bonds
• Malleability: Can be hammered into thin sheets
• Ductility: Can be drawn into wires
• Conductivity: Good conductors of heat and electricity (due to mobile electrons)
• Appearance: Lustrous (shiny)
• Strength: High tensile strength, can hold heavy weight
• Sound: Make ringing sound when hit
• Hardness: Hard substances
• Physical state: Usually solids with high melting/boiling points (except mercury)

Non-metals:

• Gain electrons easily to form negative ions (anions)
• Variety of colors and physical states
• Cannot be beaten into sheets (brittle)
• Cannot be drawn into wires
• Poor conductors of heat and electricity (except graphite)
• Dull appearance (except iodine)
• Not strong, low tensile strength
• Low melting and boiling points (except graphite and diamond)
• Low densities compared to metals