SSC CGL · Bite-size lessons

Chemistry

About 7 min · General Awareness · English

Time worked out from the lesson's 458 words at 150 words a minute, plus a minute for each question.

The exam tests foundational concepts from three areas: the periodic table and atomic structure, acid-base chemistry and pH, and basic organic chemistry including hydrocarbons and functional groups. Unlike board exams that require detailed derivations, SSC focuses on fact recall, simple applications, and real-world connections—think everyday chemicals, common reactions, and properties you can observe.

Key ideas

• Periodic Table Organization: Elements are arranged by increasing atomic number in 18 groups (vertical columns) and 7 periods (horizontal rows). Groups contain elements with similar chemical properties because they have the same number of valence electrons.
• Metals, Non-metals, Metalloids: Metals (left and center) are malleable, ductile, good conductors, and form positive ions. Non-metals (right side) are brittle, poor conductors, and form negative ions. Metalloids (B, Si, Ge, As, Sb, Te) show intermediate properties.
• Acids and Bases: Acids release H⁺ ions in water (HCl, H₂SO₄, HNO₃), taste sour, turn blue litmus red. Bases release OH⁻ ions (NaOH, Ca(OH)₂), taste bitter, feel slippery, turn red litmus blue. pH scale runs 0–14: below 7 is acidic, 7 is neutral, above 7 is basic.
• Salt Formation: Acid + Base → Salt + Water (neutralization). The salt's nature depends on the strength of the parent acid and base. Strong acid + strong base = neutral salt (NaCl). Weak acid + strong base = basic salt (sodium acetate).
• Organic Chemistry Basics: Organic compounds contain carbon-hydrogen bonds. Hydrocarbons are pure C-H compounds: alkanes (single bonds, C_nH_{2n+2}), alkenes (double bonds, C_nH_{2n}), alkynes (triple bonds, C_nH_{2n-2}).

Watch out for

• Confusing atomic number with mass number: Atomic number = number of protons (defines the element). Mass number = protons + neutrons (defines the isotope). Iron is always atomic number 26, but mass can be 54, 56, or 57.
• pH scale direction errors: Students remember "7 is neutral" but forget which direction is acidic. Fix: Lower pH = more acidic = more H⁺ ions. Lemon juice (pH 2) is more acidic than vinegar (pH 3).
• Mixing up alkane/alkene/alkyne formulas: Remember the pattern—each step removes 2 hydrogens. Alkane C₂H₆ (ethane), alkene C₂H₄ (ethene), alkyne C₂H₂ (ethyne). Double bond = –2H, triple bond = –4H from saturated.

Quick reference

• Periodic table: 18 groups, 7 periods; atomic number = protons; group number (old system) ≈ valence electrons for main groups.
• pH scale: 0–6 acidic, 7 neutral, 8–14 basic; each step is 10× concentration change.
• Strong acids: HCl, H₂SO₄, HNO₃; Strong bases: NaOH, KOH, Ca(OH)₂.
• Hydrocarbons: Alkanes (–C–C–), alkenes (–C=C–), alkynes (–C≡C–); all burn in oxygen.
• Key functional groups: –OH alcohol, –COOH acid, –CHO aldehyde, –CO– ketone.

Check yourself: 3 questions

This lesson is cut from the topic's note, not rewritten. Fact-checked on 17 Oct 2026: an AI-assisted check of this note against cited sources; the errors it found were corrected that day. Some errors may remain. The questions are from Shishya's validated question bank.

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