Quick answer: Lattice energy is the enthalpy change when one mole of an ionic solid forms from its gaseous ions under standard conditions. It is negative because lattice formation releases energy. Its magnitude increases with higher ionic charge and smaller ionic radius, and you find it from a Born-Haber cycle using Hess’s law. Lattice energyContinue reading “Lattice Energy Explained (H2 Chemistry)”
Category Archives: A Level Chemistry
Transition Metals Explained: H2 Chemistry Guide (9476)
Quick answer: A transition element is a d-block element that forms at least one stable ion with an incomplete d subshell — which is why zinc (Zn²⁺ = [Ar]3d¹⁰) doesn’t qualify despite being in the d-block. Chromium ([Ar]3d⁵4s¹) and copper ([Ar]3d¹⁰4s¹) are the two classic exceptions to the expected filling pattern. Transition metals show variableContinue reading “Transition Metals Explained: H2 Chemistry Guide (9476)”
Electronegativity Explained: H2 Chemistry Guide (9476)
Quick answer: Electronegativity is the ability of a bonded atom to attract the shared pair of electrons towards itself. It generally increases across a period — from 0.93 (sodium) to 3.16 (chlorine) on the Pauling scale — because nuclear charge rises while shielding barely changes. It generally decreases down a group, since added shells increaseContinue reading “Electronegativity Explained: H2 Chemistry Guide (9476)”
Atomic Radius Explained: H2 Chemistry Guide (9476)
Quick answer: Atomic radius decreases across a period (rising nuclear charge, shielding barely changes) and increases down a group (extra occupied shells outweigh the higher nuclear charge). Sodium’s atomic radius is 0.157 nm versus chlorine’s 0.099 nm across Period 3; magnesium’s is 0.160 nm versus barium’s 0.217 nm down Group 2. Ionic radius follows theContinue reading “Atomic Radius Explained: H2 Chemistry Guide (9476)”
Shielding Effect Explained: H2 Chemistry Guide (9476)
Quick answer: The shielding effect is the reduction in nuclear attraction felt by an outer electron because inner-shell electrons repel it — the nucleus’s charge hasn’t weakened, the outer electron simply doesn’t experience all of it. Shielding barely changes across a period, since added electrons enter the same principal shell, but increases substantially down aContinue reading “Shielding Effect Explained: H2 Chemistry Guide (9476)”
Effective Nuclear Charge: The H2 Chemistry Exam-Answering Framework (9476)
Quick answer: Most students who lose marks on “explain the trend” questions already understand effective nuclear charge — the theory isn’t the problem. The problem is structure: naming a factor without connecting it to attraction, or listing every factor instead of the one that’s actually decisive for that specific comparison. This guide gives a repeatableContinue reading “Effective Nuclear Charge: The H2 Chemistry Exam-Answering Framework (9476)”
O-Level Chemistry QA Table Explained: Complete Guide (6092)
Quick answer: The O-Level Chemistry QA table covers standard tests for 7 aqueous cations, 5 anions, and 6 gases, printed as part of Paper 3. The table alone isn’t enough — three cations (Al³⁺, Ca²⁺, Zn²⁺) all give a white precipitate with sodium hydroxide, so distinguishing them requires comparing behaviour in excess reagent and testingContinue reading “O-Level Chemistry QA Table Explained: Complete Guide (6092)”
Ionisation Energy Explained: H2 Chemistry Guide (9476)
Quick answer: Ionisation energy is the energy needed to remove an electron from a gaseous atom or ion. First ionisation energy generally increases across a period (rising nuclear charge, similar shielding) and decreases down a group (electron further from the nucleus, more shielding). Two exceptions in Period 3 — aluminium being lower than magnesium, andContinue reading “Ionisation Energy Explained: H2 Chemistry Guide (9476)”
H2 Chemistry Syllabus Explained: Complete Topic Guide (9476)
Quick answer: The H2 Chemistry syllabus (9476, first examined 2026) has 13 numbered topics organised around three Core Ideas — Matter, Structure and Properties, and Transformation — plus Extension Topics covering Organic Chemistry, Electrochemistry, and Transition Elements. Topics aren’t isolated: atomic structure supports bonding, bonding explains properties, energetics connects to equilibrium, and organic reactions drawContinue reading “H2 Chemistry Syllabus Explained: Complete Topic Guide (9476)”
H2 Chemistry Data Booklet Explained: The Complete 2026 Guide (Syllabus 9476 & 9729)
Quick answer: The H2 Chemistry Data Booklet is the official reference document issued in the theory papers for Singapore’s A-Level Chemistry (syllabuses 9476 and, for 2026, the outgoing 9729). It supplies constants, tables, and the Periodic Table — but not the formulas or methods needed to use them, which students must still know. This guideContinue reading “H2 Chemistry Data Booklet Explained: The Complete 2026 Guide (Syllabus 9476 & 9729)”
