## Overview This topic covers the nuclear atom and the idea that matter is composed of quarks and leptons. Learners study the quark composition of the neutron and the proton and the idea that quarks and antiquarks are never observed in isolation. The properties of the four interactions experienced by particles are discussed and learners are shown how to apply the conservation of charge, lepton number and quark number to given reactions. ## Working Scientifically There are opportunities within this topic for learners to present data in appropriate ways; to process and analyse using appropriate mathematical skills. Mathematical Skills There is an opportunity for learners to use ratios and fractions in this unit. ## How Science Works There are opportunities within this topic for learners to use theories, models and ideas to develop scientific explanations; to analyse and interpret data to provide evidence, recognise correlations and causal relationships; to evaluate methodology, evidence and data, and resolve conflicting evidence; to know that scientific knowledge and understanding develops over time; to evaluate the role of the scientific community in validating new knowledge and ensuring integrity. ### Learners should be able to demonstrate and apply their knowledge and understanding of: (a) the significance of the results of the Rutherford alpha particle scattering experiment (b) how to approximate the maximum size of the Coulomb repulsion force between an alpha particle and a gold atom / nucleus for both the plum pudding model and the Rutherford model (c) the idea that matter is composed of quarks and leptons and that there are three generations of quarks and leptons, although no questions will be set involving second or third generations leptons quarks particle (symbol) electron (e– ) electron neutrino (ve) up (u) down (d) charge (e) 1 0 2 3 + 1 3 − (d) the idea that antiparticles exist for the particles given in the table above, that the properties of an antiparticle are identical to those of its corresponding particle apart from having opposite charge, and that particles and antiparticles annihilate (e) symbols for a positron and for antiparticles of quarks and hadrons (f) the idea that quarks and antiquarks are never observed in isolation, but are bound into composite particles called hadrons, or three types of baryon (combinations of 3 quarks), or antibaryons (combinations of 3 antiquarks) or mesons (quark-antiquark pairs) (g) the quark compositions of the neutron and proton (h) how to use data in the table on page 45 to suggest the quark make-up of less well known first generation baryons and of charged pions (i) the properties of the four forces or interactions experienced by particles as summarized in the table below Interaction Experienced by Range Comments gravitational all matter infinite very weak – negligible except between large objects such as planets weak all leptons, all quarks, so all hadrons very short only significant when the e-m and strong interactions do not operate electromagnetic (e-m) all charged particles infinite also experienced by neutral hadrons, as these are composed of quarks strong all quarks, so all hadrons short (j) how to apply conservation of charge, lepton number and baryon number (or quark number) to given simple reactions (k) the idea that neutrino involvement and quark flavour changes are exclusive to weak interaction