IGCSE 0625 · NUCLEAR · 5.1

The nuclear model of the atom

The nuclear model of the atom: a tiny dense nucleus of protons and neutrons surrounded by electrons, nuclide notation, isotopes, and the Extended alpha-scattering evidence. It leads into radioactivity.

TOPIC 5.1: THE NUCLEAR MODEL OF THE ATOM CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 2.1 Particle model LEADS TO 5.2 Radioactivity Elements & isotopes THE ATOM 1 · INSIDE THE ATOM An atom has a tiny, dense, positive nucleus with electrons moving around it. The nucleus holds nearly all the mass. Electrons (negative) sit in shells around it. Most of the atom is empty space. + nucleus and electron shells 2 · THE NUCLEUS The nucleus is made of protons and neutrons, together called nucleons. Proton: positive charge. Neutron: no charge. The proton number Z decides which element it is. The nucleon number A = protons + neutrons. A Z X A = nucleon number Z = proton number X = element symbol example: carbon is written C with A=12, Z=6 3 · ISOTOPES Isotopes are atoms of the same element with different numbers of neutrons. Same proton number, different nucleon number. They behave the same way chemically. Example: carbon-12 and carbon-14. carbon-12 6 protons, 6 neutrons carbon-14 6 protons, 8 neutrons red = proton grey = neutron 4 · THE SCATTERING EVIDENCE EXTENDED Firing alpha particles at thin gold foil revealed the nucleus. Most passed straight through: the atom is mostly empty space. A few were deflected: the nucleus is positive. Very few bounced back: it is tiny and dense. gold foil nucleus
TOPIC 5.1: THE NUCLEAR MODEL OF THE ATOM CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 2.1 Particle model LEADS TO 5.2 Radioactivity Elements & isotopes THE ATOM 1 · INSIDE THE ATOM An atom has a tiny, dense, positive nucleus with electrons moving around it. The nucleus holds nearly all the mass. Electrons (negative) sit in shells around it. Most of the atom is empty space. + nucleus and electron shells 2 · THE NUCLEUS The nucleus is made of protons and neutrons, together called nucleons. Proton: positive charge. Neutron: no charge. The proton number Z decides which element it is. The nucleon number A = protons + neutrons. A Z X A = nucleon number Z = proton number X = element symbol example: carbon is written C with A=12, Z=6 3 · ISOTOPES Isotopes are atoms of the same element with different numbers of neutrons. Same proton number, different nucleon number. They behave the same way chemically. Example: carbon-12 and carbon-14. carbon-12 6 protons, 6 neutrons carbon-14 6 protons, 8 neutrons red = proton grey = neutron 4 · THE SCATTERING EVIDENCE EXTENDED Firing alpha particles at thin gold foil revealed the nucleus. Most passed straight through: the atom is mostly empty space. A few were deflected: the nucleus is positive. Very few bounced back: it is tiny and dense. gold foil nucleus
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