ACT SSC Chemistry · Unit 2
ACT SSC Chemistry Unit 2: Molecules — Flashcards & Quiz
ACT SSC Chemistry Unit 2 covers molecules within the BSSS framework. This unit explores molecular structure, Lewis structures, VSEPR theory, intermolecular forces, properties of molecular substances and chemical reactions. These flashcards and quiz questions help you revise the key concepts tested in ACT assessments.
Key Terms
- Molecular Geometry
- The three-dimensional arrangement of atoms within a molecule as predicted by VSEPR theory, considering both bonding and lone pairs; a core skill in BSSS Chemistry Unit 2 school-based assessments.
- Intermolecular Forces
- The attractive forces between molecules, including dispersion forces, dipole-dipole interactions and hydrogen bonding; BSSS assessments require linking these forces to physical properties such as boiling point and solubility.
- Hydrogen Bonding
- A strong type of dipole-dipole attraction occurring when hydrogen is bonded to highly electronegative atoms (N, O, F); explains anomalous properties like water's high boiling point in ACT SSC Chemistry.
- Polarity
- The uneven distribution of electron density in a molecule due to differences in electronegativity, resulting in a dipole moment; predicting polarity from molecular shape is a key ACT SSC skill.
- Structural Isomerism
- The existence of molecules with the same molecular formula but different structural arrangements of atoms; identifying and naming structural isomers is assessed in BSSS organic chemistry tasks.
- Functional Group
- A specific group of atoms within a molecule that determines its chemical reactivity and properties, such as hydroxyl (-OH) or carboxyl (-COOH); recognising functional groups is essential for ACT SSC organic nomenclature.
- Dispersion Forces
- Weak intermolecular attractions arising from temporary dipoles caused by random electron movement; present in all molecules and increasing with molecular size, as tested in BSSS property comparison questions.
Sample Flashcards
Q1: Explain collision theory.
Collision theory states that for a reaction to occur, reactant particles must collide with sufficient energy (activation energy) and correct orientation. Not all collisions lead to reaction — only effective (successful) collisions do.
Q2: List four factors that affect the rate of a chemical reaction.
1) Temperature — increases particle energy and collision frequency. 2) Concentration/pressure — increases collision frequency. 3) Surface area — exposes more particles. 4) Catalyst — lowers activation energy.
Q3: What is activation energy (Ea)?
Activation energy is the minimum amount of energy that colliding particles must have for a successful reaction to occur. It represents the energy barrier between reactants and products on an energy profile diagram.
Q4: How does a catalyst increase the rate of reaction?
A catalyst provides an alternative reaction pathway with a lower activation energy, allowing a greater proportion of particles to have enough energy for successful collisions. The catalyst is not consumed and is regenerated.
Q5: Distinguish between endothermic and exothermic reactions.
Exothermic: releases energy to surroundings, ΔH is negative, products have less energy than reactants. Endothermic: absorbs energy from surroundings, ΔH is positive, products have more energy than reactants.
Q6: What is chemical equilibrium?
Chemical equilibrium occurs in a reversible reaction when the rate of the forward reaction equals the rate of the reverse reaction. The concentrations of reactants and products remain constant (but not necessarily equal). It is a dynamic process.
Q7: State Le Chatelier’s principle.
If a system at equilibrium is subjected to a change in concentration, temperature or pressure, the system will shift to partially oppose the change and establish a new equilibrium.
Q8: How does changing temperature affect equilibrium?
Increasing temperature favours the endothermic direction (absorbs excess heat). Decreasing temperature favours the exothermic direction (releases heat). Temperature is the only factor that changes the value of Keq.
Sample Quiz Questions
Q1: All collisions between reactant particles result in a chemical reaction.
Answer: FALSE
Only collisions with sufficient energy (exceeding activation energy) AND correct orientation result in reaction.
Q2: Increasing surface area increases the rate of reaction.
Answer: TRUE
Greater surface area exposes more reactant particles, increasing the frequency of collisions.
Q3: Activation energy is the total energy released during a reaction.
Answer: FALSE
Activation energy is the MINIMUM energy needed for reactants to form products, not the energy released.
Q4: A catalyst is consumed during the reaction.
Answer: FALSE
A catalyst is NOT consumed. It participates in the reaction but is regenerated and can be reused.
Q5: An exothermic reaction has a negative ΔH value.
Answer: TRUE
Exothermic reactions release energy, so products have less energy than reactants, giving a negative ΔH.
Why It Matters
Molecules in ACT SSC Chemistry Unit 2 explores how atoms combine to form molecular substances with distinct structures and properties. BSSS assessments test your ability to draw Lewis structures, predict molecular shapes using VSEPR theory, identify intermolecular forces, and explain how molecular structure determines physical and chemical properties. This unit develops both your structural reasoning and your ability to connect nanoscale molecular features to macroscopic behaviour. Students who understand how molecular shape influences polarity and intermolecular forces find they can predict properties of unfamiliar substances with confidence. Intermolecular force concepts from this unit directly support the equilibrium module, where boiling points and solubility trends depend on understanding dispersion forces, dipole interactions, and hydrogen bonding. BSSS exam questions on molecules commonly require you to predict and explain physical properties from a Lewis structure, so practise the full sequence of drawing the structure, determining shape with VSEPR, assessing polarity, and identifying the dominant intermolecular force.
Key Concepts
Molecular Structure and Lewis Diagrams
Drawing accurate Lewis structures and identifying bonding and lone pairs is the starting point for predicting molecular properties. BSSS assessments test your ability to construct Lewis diagrams for covalent molecules and polyatomic ions, and to use them as the basis for shape and polarity analysis.
VSEPR Theory and Molecular Shape
VSEPR theory predicts three-dimensional molecular geometry from electron pair repulsion. Understanding how bonding pairs and lone pairs determine shape, and linking shape to bond angles and molecular symmetry, is a core skill for BSSS Chemistry assessments.
Intermolecular Forces and Properties
Dispersion forces, dipole-dipole interactions, and hydrogen bonding determine boiling points, solubility, and other physical properties. Identifying the dominant intermolecular force in a substance and explaining its effect on macroscopic properties is frequently assessed.
Introduction to Organic Molecules
Hydrocarbons, functional groups, and IUPAC nomenclature introduce the systematic study of carbon-based molecules. Recognising structural features, naming simple organic compounds, and understanding how functional groups determine reactivity provides the foundation for later organic chemistry study.
Common Mistakes to Avoid
- Predicting molecular shape using only bonding pairs and ignoring lone pairs — BSSS VSEPR questions require you to count all electron pairs around the central atom, as lone pairs significantly alter geometry.
- Claiming that hydrogen bonding occurs whenever hydrogen is present in a molecule — ACT SSC examiners require hydrogen to be bonded to N, O or F and for there to be a lone pair on an adjacent electronegative atom.
- Ranking intermolecular forces incorrectly by assuming dispersion forces are always the weakest — in large non-polar molecules, dispersion forces can exceed dipole-dipole forces of smaller polar molecules; BSSS assessments test this nuance.
- Drawing structural isomers that are actually the same molecule rotated or flipped — ACT Board of Senior Secondary Studies marking guides require genuinely different connectivity between atoms for each isomer.
Study Tips
- Practise drawing Lewis structures for ten different molecules daily, checking each against VSEPR predictions for shape and polarity.
- Build flashcards for molecular shapes, bond angles, and intermolecular forces, reviewing with spaced repetition for automatic recall.
- Create a summary table linking molecular structure to physical properties like boiling point, solubility and viscosity for comparison questions.
- Work through naming organic compounds from structural formulae and drawing structures from IUPAC names until the process becomes fluent.
- Use molecular model kits or 3D visualisation software to develop spatial reasoning about molecular geometry and isomerism.
- Before your exam, work through the practice questions in this set at least twice using spaced repetition. Testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Frequently Asked Questions
What does ACT SSC Chemistry Unit 2 cover?
Unit 2 covers molecules including molecular structure, Lewis structures, VSEPR theory, intermolecular forces, properties of molecular substances, organic chemistry fundamentals and chemical reactions.
How many flashcards are in this set?
This free set contains 20 flashcards and 20 true/false quiz questions covering all key concepts in Unit 2, aligned to the BSSS Chemistry framework.
Are these flashcards aligned to the ACT curriculum?
Yes — every flashcard and quiz question is mapped to the BSSS Science Framework for ACT SSC Chemistry Unit 2.
Last updated: March 2026 · 20 flashcards · 20 quiz questions · Content aligned to the BSSS Framework