Basic Chemistry — Study Notes for UPSSSC PET

Overview

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). This topic intersects with everyday life—medicines, fertilizers, fuels, cleaning agents—making it both scoring and practical. Expect 4–6 questions directly from this domain, often phrased as "Which compound is used in X?" or "What happens when acid reacts with metal?"

Your preparation strategy should prioritize common compounds and their uses, acid-base indicators, types of bonds, and the periodic table's basic organization. Avoid deep dive into quantum mechanics or complex organic chemistry; PET tests breadth, not depth. A solid grasp of NCERT Class 9–10 chemistry suffices for 90% of questions.

Key Concepts

• **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.

• **Common compounds in daily life**: NaCl (table salt), NaHCO₃ (baking soda), CaCO₃ (limestone/marble), CaO (quicklime), Ca(OH)₂ (slaked lime), NaOH (caustic soda), H₂SO₄ (battery acid).

• **Metals vs nonmetals**: Metals are lustrous, malleable, ductile, good conductors; tend to lose electrons. Nonmetals are brittle, poor conductors (except graphite); tend to gain electrons. Metalloids (Si, Ge) have intermediate properties.