Fun7.1 the nuclear atom notes
- 1. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom The Atom http://www.youtube.com/watch?v=DwqYsoDqbCQ Learning Objectives • I can describe the Geiger-Marsden Experiment • I can describe how these results explain Rutherford’s Model of the nuclear atom • I can define a nucleus in terms of Proton Number and Nucleon Number • I know how ISOTOPES occur • I know that some isotopes are UNSTABLE and undergo a RANDOM process of radioactive decay • I know that Alpha, Beta and Gamma radiation is emitted when an unstable nucleus decays • I know the nature of Alpha, Beta and Gamma radiation and their defferent penetration The Scientific Process Phenomena → hypothesis → prediction → investigate/experiments → theory → Law 1
- 2. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom Earlier Models of the Atom; JJ Thompson – Plum Pudding Geiger-Marsden Experiment – Alpha Particle Scattering by a Gold Foil The results of this experiment were: • The large majority of the alpha particles go straight and are not deflected • A small number of alpha particles are deflected through a small angle. • A very small number of alpha particles are deflected through a large angle (rebound) 2 Florescent screen Large majority of flashes occur straight ahead Small number of α particles are deflected Very small number of α particles deflected at a large angle
- 3. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom Rutherford’s Model of the Nuclear Atom The observations from the Geiger-Marsden experiment were used by Rutherford and led him to propose the theory of the nuclear atom. Observation from the Geiger-Marsden Experiment Hypothesis proposed by Rutherford Large majority of the α particles go straight through the gold leaf Most of an atom is ......... space and therefore the mass of the atom must be held in a small region, called the .......... Some of the α particles are scattered. No useful hypothesis can be considered. A very small number of positively charged α particles undergo LARGE ANGLE SCATTERING. (repelled back through more than 90o ) There must be a …….., …………… charged nucleus, that contains almost all of the ………….. of the atom. Other advancements (not required): • Niels Bohr postulated the quantum energy levels of the electrons. • 1932 Neutrons discovered by James Chadwick. 3
- 4. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom What Affects the Scattering of the Alpha Particles (required) What affects the amount of deflection? 1. Charge – the alpha particles are positively charged that is why they experience ............... from the ............ charged nucleus. 2. Speed – Particles B and F are moving ............... than particle A. They experience a smaller deflection because they spend ........... time close to the nucleus. 3. Proximity to the nucleus – only the very small number of alpha particles that pass very close to the ............. experience enough repulsion for ‘large angle scattering’ such as particle D. The Rutherford-Bohr / Standard Model of the Atom 4
- 5. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom 5 Positive protons Neutral Neutrons Negative electrons
- 6. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom Atomic Symbols Eg. Carbon Z for example 6 is the proton number / atomic number, which is the number of protons in the nucleus. The proton number defines the element. A, for example 12 is the mass number / nucleon number which is the number of protons plus neutrons in the nucleus. Isotopes A given element is defined by the given number of protons. However the number of neutrons can change. An isotope is different version of the same ……….. that has a different number of ……………. Radio-isotopes Since neutrons play an important role in binding the nucleus together, too ……… or too ……… neutrons will affect the stability of the nucleus. A radio-isotope has an unstable nucleus that can, at any moment, decay in order to try and achieve stability. 6 C 12 6 C A Z
- 7. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom Radioactive Decay Decay is a random process by which an alpha or beta particle or a gamma photon is emitted from an ………….. nucleus which is trying to become stable. Radioactive Particles http://www.youtube.com/watch?v=N8JRqW1-my4&NR=1 http://www.youtube.com/watch?v=9j62CVRwZPc Name Symbol Nature Sources Ionising Power Penetratio n Stopped by Range in air Alpha α ……….. Nucleus 4 He2+ Larger nuclei Eg. 208 Po High Low ……… 2-3cm Beta β An ……… -1β-1 smaller nuclei eg. 40 K Medium Medium 1-2cm of …….. Few feet Gamma γ An EM wave. A packet of ……. called a PHOTON. Eg. 99 Tc low high Several inches of ……. kms Homework Page 253 Q 1-4 7
- 8. FUNDAMENTAL Physics – Atomic Physics: 7.1 The Nuclear Atom For this topic please make use of www.furryelephant.com which has many electricity animations and explanations. School username: islandschool School password: islandscience This was expensive, but it is very very good. The Wall http://www.youtube.com/watch?v=M_bvT-DGcWw 8