Rucete ✏ SAT Chemistry In a Nutshell
13. Some Representative Groups and Families
This chapter introduces the sulfur, halogen, and nitrogen families, key metals and their compounds, and the concept of alloys and metalloids. You’ll learn to recognize common properties, reactions, and applications of elements that frequently appear in SAT Chemistry questions.
Sulfur Family
- Sulfur is the most discussed element in this family (oxygen was covered earlier).
- Found naturally in volcanic areas (Japan, Mexico, Sicily). Extracted by heating rock mixtures.
- Exists in several allotropic forms (rhombic, monoclinic, amorphous).
Sulfuric Acid (H₂SO₄)
- Strong diprotic acid that ionizes in two steps:
- First ionization forms HSO₄⁻ (acid salt)
- Second ionization forms SO₄²⁻ (normal salt)
- Has three key roles:
- As an acid
- As an oxidizing agent (e.g., Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O)
- As a dehydrating agent, especially with carbohydrates
Hydrogen Sulfide (H₂S)
- Colorless, rotten egg smell, poisonous at low concentrations
- Formed by: FeS + 2HCl → FeCl₂ + H₂S
- Burns in air:
- With sufficient O₂: forms SO₂ + H₂O
- With limited O₂: may form elemental sulfur
- Used in lab tests due to formation of colorful sulfide precipitates: ZnS (white), CdS (bright yellow), As₂S₃ (lemon yellow), CuS (black), PbS (brown-black)
Sulfur Dioxide (SO₂)
- Colorless gas with suffocating odor
- Shows resonance structures → actual bonding is a hybrid
- Also see SO₃, another molecule with resonance
Halogen Family
- Group 17 (VIIA): Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)
- All are diatomic (X₂) and show −1 oxidation state most commonly, but can also show +1, +3, +5, +7 in oxyanions
- Fluorine is the most reactive and strongest oxidizing agent; forms only −1 oxidation state
- Halogens react with metals to form halide salts (e.g., NaCl, CaBr₂)
Hydrohalic Acids and Silver Halides
- HX acids:
- HCl, HBr, HI are strong acids
- HF is weak but highly corrosive (attacks glass)
- Halide detection with AgNO₃:
- AgCl: white
- AgBr: pale yellow
- AgI: yellow
Chlorine and Its Compounds
- Cl₂: greenish gas with strong odor; used in bleach and disinfection
- Reacts with water: Cl₂ + H₂O ⇌ HCl + HOCl (hypochlorous acid, disinfectant)
- Bleaching reaction: Cl₂ + cold, dilute NaOH → NaCl + NaOCl + H₂O
- NaClO (sodium hypochlorite) is the active ingredient in bleach
Nitrogen Family
- Group 15 (VA): N, P, As, Sb, Bi
- Show oxidation states from −3 to +5
Nitric Acid (HNO₃)
- Strong monoprotic acid and powerful oxidizing agent
- Colorless when pure, turns yellow due to NO₂
- Reactions:
- Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O
- 2HNO₃ + SO₂ → 2H₂SO₄ + NO
- Decomposes on light → stored in dark bottles
- Forms nitrates: all are soluble
Ammonia (NH₃)
- Colorless gas with pungent odor, lighter than air
- Very soluble in water, forms NH₄⁺ and OH⁻
- Lab prep: NH₄Cl + Ca(OH)₂ → NH₃ + CaCl₂ + H₂O
- Used in fertilizers, cleaning agents, and explosives (e.g., ammonium nitrate)
General Properties of Metals
- Physical properties:
- Good conductors of heat and electricity
- Malleable and ductile
- Luster (shiny)
- High melting points (except mercury)
- Chemical properties:
- Form positive ions (cations)
- React with acids to release H₂ gas
- Form basic oxides (e.g., Na₂O, CaO)
Metallurgy (Metal Extraction)
- Ores: naturally occurring compounds from which metals can be extracted
- Common extraction methods:
- Roasting: sulfide → oxide (e.g., ZnS → ZnO + SO₂)
- Reduction with carbon or electrolysis (e.g., Fe₂O₃ + 3C → 2Fe + 3CO)
- Blast furnace used for iron: Iron ore + coke + limestone → Fe + slag + CO₂
- Refining: Purifying impure metal via electrolysis, distillation, etc.
Representative Metals
- Iron (Fe):
- Used in steel (Fe + C)
- Forms Fe²⁺ and Fe³⁺
- Copper (Cu):
- Excellent conductor
- Cu²⁺ forms blue solution
- Zinc (Zn):
- Used in galvanizing
- Amphoteric: reacts with acids and bases
- Silver (Ag):
- Best electrical conductor
- Used in jewelry, photography
- Mercury (Hg):
- Liquid at room temperature
- Forms toxic compounds
Alloys
- Mixtures of metals (or with nonmetals) to enhance properties
- Common alloys:
- Steel: Fe + C
- Brass: Cu + Zn
- Bronze: Cu + Sn
- Solder: Pb + Sn
- Sterling silver: Ag + Cu
- Amalgam: Hg + other metal
- Alloys are often stronger, harder, or more corrosion-resistant than pure metals
Metalloids
- Elements with properties of both metals and nonmetals
- Found along the stair-step line in the periodic table
- Common metalloids: Boron (B), Silicon (Si), Arsenic (As), Tellurium (Te)
- Used in semiconductors, solar cells, and computer chips
In a Nutshell
Representative groups like the sulfur, halogen, and nitrogen families display predictable chemical behavior and unique compounds. Metals are extracted and refined for use in construction, electronics, and alloys. Metalloids bridge the gap between metals and nonmetals. Recognizing the properties and reactions of these groups helps you understand periodic trends and apply chemistry in real-world contexts and SAT problems.