UPSSSC PET · Bite-size lessons

Basic Chemistry

About 7 min · General Science · English

Time worked out from the lesson's 537 words at 150 words a minute, plus a minute for each question.

Basic Chemistry forms a core component of the General Science section in UPSSSC PET. Questions typically test fundamental concepts rather than advanced calculations: atomic structure basics, types of chemical bonds, properties of acids and bases, and identification of common compounds used in daily life. Most questions are factual recall—knowing valencies, chemical formulas, pH values, and practical applications of substances. Students must balance memorization of key facts (like "baking soda = NaHCO₃") with conceptual clarity (why ionic compounds conduct electricity when dissolved).

Key ideas

• Atom and subatomic particles: An atom consists of a nucleus (protons + neutrons) surrounded by electrons in shells. Protons are positive, electrons negative, neutrons neutral. Atomic number = number of protons; mass number = protons + neutrons.
• Electronic configuration: Electrons occupy shells (K, L, M, N) with maximum capacities 2, 8, 18, 32. Valence electrons (outermost shell) determine chemical behavior. Example: Sodium (11) has configuration 2, 8, 1 → easily loses 1 electron.
• Chemical bonding: Ionic bonds form by electron transfer (metal + nonmetal), creating charged ions; covalent bonds form by electron sharing (nonmetal + nonmetal). Metallic bonding involves a "sea of electrons" among metal atoms.
• Acids, bases, salts: Acids taste sour, turn blue litmus red, release H⁺ in water (HCl, H₂SO₄). Bases taste bitter, turn red litmus blue, release OH⁻ (NaOH, Ca(OH)₂). Salts form when acid reacts with base (neutralization).
• pH scale: Measures acidity/alkalinity from 0–14. pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic. Stomach acid ~pH 2, pure water pH 7, soap ~pH 10.

Watch out for

• Confusing atomic number with mass number: Atomic number = protons only; mass number = protons + neutrons. Students often mix these, especially when calculating neutrons (neutrons = mass number − atomic number).
• Writing incorrect chemical formulas: Writing NaCl₂ instead of NaCl. Fix: Always cross-check valency. Sodium has valency 1, chlorine 1 → NaCl (1:1 ratio).
• Thinking all white powders are the same: Confusing salt (NaCl), sugar (C₁₂H₂₂O₁₁), baking soda (NaHCO₃), washing soda (Na₂CO₃·10H₂O). Fix: Memorize specific uses and chemical names. Salt = seasoning, baking soda = baking/antacid, washing soda = cleaning.

Quick reference

• Atomic structure: Proton (+), electron (−), neutron (neutral). Atomic number = protons. Mass number = protons + neutrons.
• Ionic bond: Electron transfer, forms between metal and nonmetal (e.g., NaCl). Covalent bond: Electron sharing, forms between nonmetals (e.g., H₂O).
• Acid + Base → Salt + Water (neutralization). Metal + Acid → Salt + H₂ gas.
• pH scale: 0–6 acidic, 7 neutral, 8–14 basic. Litmus: red → acid, blue → base.
• Common compounds: NaCl (salt), NaHCO₃ (baking soda), CaCO₃ (marble/limestone), NaOH (caustic soda), H₂SO₄ (battery acid).

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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