JPJC 2026 Atomic Structure Lecture Notes

2026 JPJC JC1 H2 Chemistry (9476) 1 Topic 1: Atomic Structure Jurong Pioneer Junior College 2026 JC1 H2 Chemistry (9476) Core Idea 1 – Matter Topic 1: Atomic Structure Recommended Reference Books: 1. Cambridge International as and A Level Chemistry by Peter Cann and Peter Hughes 2. A-Level Chemistry (4th Edition) by E N Ramsden 3. Chemistry in Context (6th Edition) by Graham Hill and John Holman Web-based Resources: No Description QRCode No Description QRCode 1 Online Chemistry Website: Chemguide. https://bit.ly/3qtzdwF 2 2400 years of hard work in the development of the atomic model. https://bit.ly/3nWdSdr 3 An Introduction to the history of Atomic Chemistry. https://bit.ly/2LGbafd 4 Rutherford Gold Foil Experiment (Part 1). https://bit.ly/3nUtfmR 5 Rutherford Gold Foil Experiment (Part 2). https://bit.ly/2LVPlrY 6 3D V isualisation of Atomic Orbitals. https://bit.ly/3qnTIuw Learning Outcomes Candidates should be able to: (a) identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses (b) deduce the behaviour of beams of protons, neutrons and electrons in an electric field (c) describe the distribution of mass and charges within an atom (d) deduce the numbers of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge) (e) (i) describe the contribution of protons and neutrons to atomic nuclei in terms of proton number and nucleon number (ii) distinguish between isotopes on the basis of different numbers of neutrons present (f) describe the number and relative energies of the s, p and d orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p orbitals (g) describe the shapes of s, p and d orbitals (see also Section 13) [knowledge of wave functions is not required] (h) state the electronic configuration of atoms and ions given the proton number (and charge) (i) explain the factors influencing the ionisation energies of elements (see the Data Booklet) (see also The Periodic Table) (j)* recognise variation in the electronic configurations across a Period and down a Group (k)* describe and explain qualitatively the trends and variations in atomic radius, ionic radius, first ionisation energy and electronegativity: (i) across a Period in terms of shielding and nuclear charge (ii) down a Group in terms of increasing number of electronic shells , shielding and nuclear charge (l) deduce the electronic configurations of elements from successive ionisation energy data (m) interpret successive ionisation energy data of an element in terms of the position of that element within the Periodic Table * LOs from The Periodic Table

2026 JPJC JC1 H2 Chemistry (9476) 2 Topic 1: Atomic Structure Contents: Section Content LOs 1 The Sub–atomic Particles 1.1 Three fundamental sub–atomic particles (a) 1.2 Behaviour of particles in electric field (b) 1.3 Proton number and Nucleon Number (c), (d), (e) 1.4 Type of species (Isotopes) recall 2 Electronic Energy Levels and Sub–Levels 2.1 Historical perspective of the structure of atoms − 2.2 Principal quantum shells, subshells & orbitals (f) 2.3 Atomic orbitals and shapes of atomic orbitals (g) 2.4 Relative energies of atomic orbitals (f) 3 Electronic Configuration 3.1 Representation of electronic configuration (f) 3.2 Rules for writing electronic configuration (f) 3.3 Electronic configuration and the Periodic Table (j) 4 Radius 4.1 Factors affecting radius (k) 4.2 Trends in radius (k) 5 Ionisation energies 5.1 Factors affecting ionisation energies (k) 5.2 Trends in first ionisation energies (k) 5.3 Successive ionisation energies (l), (m) 6 Electronegativities (k) 1 THE SUB–ATOMIC PARTICLES 1.1 THREE FUNDAMENTAL SUB–ATOMIC PARTICLES OF MATTER (a) identify & describe protons, neutrons & electrons in terms of their relative charges & relative masses Atoms are made up of 3 fundamental particles: electron, proton and neutron. relative charge relative mass mass / kg position within an atom Deflection in an electric field (Refer 1.2) electron −1 1 1840 9.11  10−31 around nucleus Towards positive electrode proton +1 1 1.67  10−27 in nucleus Towards negative electrode neutron 0 1 1.67  10−27 in nucleus Not deflected Note: A nucleon is either a proton or a neutron. me, mp and mp are given in the Data-Booklet. 1.1.1 The nucleus is very small, compact and it made up almost the entire mass of the atom. It is positively charged. 1.1.2 The rest of the atom consists of empty spaces where the electrons are found. The negatively charged electrons are attracted ____________________ to the positively charged nucleus. 1.1.3 Atoms are ______________________ (i.e. no. of protons = no. of electrons).

2026 JPJC JC1 H2 Chemistry (9476) 3 Topic 1: Atomic Structure 1.2 BEHAVIOUR OF SUB–ATOMIC PARTICLES IN ELECTRIC FIELD (b) deduce the behaviour of beams of protons, neutrons and electrons in an electric field • The three subatomic particles behave differently in an electric field due to their relative masses and charges. • Neutrons are not deflected in an electric field as they are electrically neutral (no electrical charge). 1.2.1 Direction of Deflection depends on the charge on the particle. (i.e. opposite charges attracts). In an electric field, Things to note: • Deflection only starts when the beam enters the electric field. • Deflection of beams of electrons and protons occurs within the electric field in a parabolic path. • Beam continues a straight-line path after leaving electric field. • Angle of deflection α < Angle of deflection β (see 1.2.2 to explain the difference) 1.2.2 Angle of Deflection depends on: (a) charge of particle, q : Greater the charge, greater the extent of deflection. (b) mass of particle, m : Greater the mass, smaller the extent of deflection. , , charge qangle of deflection mass m (i.e. ( ) ( )  = charge mass 22 charge 1 mass 1 ) Exercise 1: When separate beams of 1H+ and 16O2− are passed through an electric field as shown in the diagram below, the particles behave differently. Only the beam of ¹H⁺ is shown in the diagram. (a) Sketch and label on the diagram how a beam of ¹⁶O ₂ would be affected by the electric field. (deflected towards +ve plate) (deflected towards −ve plate)   Source (not deflected) electrons + – neutrons protons source 1H+ − + 10°

2026 JPJC JC1 H2 Chemistry (9476) 4 Topic 1: Atomic Structure (b) Given that the angle of deflection of 1H+ is 10°, calculate the angle of deflection of 16O2−. (Note: If a sign is given with the angle of deflection, then include the sign in your answer. The sign reflects the direction of the beam.) Refer to Tutorial Qn 6. 1.3 PROTON NUMBER & NUCLEON NUMBER (c) describe the distribution of mass and charges within an atom (d) deduce the numbers of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge) (e) (i) describe the contribution of protons and neutrons to atomic nuclei in terms of proton number & nucleon number (ii) distinguish between isotopes on the basis of different numbers of neutrons present 1.3.1 Atomic Symbol is represented as: X = symbol of the element A = proton number (or atomic number)  no. of p Z = nucleon number (or mass number)  no. of p + n Things to note: • The proton number defines the identity of an element and is unique for each elem