Atomic Physics Atomic Notation A X Z X – symbol of the atom Z – atomic number (no of protons) A – mass number 14 C 6 C – carbon Z = 6, the number of protons in the nucleus A = 14, the number or protons plus the number of neutrons in the nucleus A is also known as the nucleon number, the number of particles in the nucleus

Atomic Physics Atomic Notation 56 Fe 26 Fe - iron the number of protons = 26 the number of neutrons = 30 the number of electrons = H 1 H - hydrogen the number of protons = 1 the number of electrons = 1 the number of neutrons = ??

Atomic Physics Isotopes Isotopes are variations of the same elements. Their nuclei contain the same number of protons but a different number of neutrons 12 C 6 13 C 6 14 C 6 Isotopes of carbon

Atomic Physics Nuclear Reactions 4 Al + 3 O 2 2 Al Al 3+ loses 3 electrons O 2- gains 2 electrons In a chemical reaction it is the movement of electrons that brings about the formation of compounds

Atomic Physics Nuclear Reactions 2 H H 1 4 He n 0 +energy A nuclear reaction involves nuclei only. Electrons don’t play a significant part

Atomic Physics Atomic Notation + energy Two small nuclei have collided to form a larger nuclei plus a neutron with the release of energy (fusion)

Atomic Physics Radioactivity: 238 U + 1 n 144 Ba 92 Kr 3 1 n A large nuclei is broken up into 2 smaller nuclei with the release of energy (fission) BeforeAfter No of protons Nucleon number This demonstrates two conservation laws: 1.Conservation of charge: No. of protons before = no. protons afterwards 2.Conservation of nucleon number: total number of protons and neutrons stays the same

Atomic Physics Example 235 U + 1 n a Xe 94 Sr 2 1 n b 0 Find the values of a and b.

Atomic Physics Examples: 226 Ra 222 Rn 4 He Radium 226 Radon α particle RadiumRadonα - particle protons88862 neutrons The radium nucleus emits an α particle (a helium nucleus) and changes into a radon nucleus.

Atomic Physics 14 C N 0 e Carbon 14 Nitrogen 14 + β particle CarbonNitrogenβ - particle protons670 neutrons870 1 n 1 p 0 e + 01 A carbon nucleus emits an electron as a neutron is converted into a proton

Atomic Physics 60 Co 60 Ni * 0 e Ni* 60 Ni γ Ni* is a Ni nucleus in an excited state. It returns to ground state by emitting a photon 28

Atomic Physics Radioactivity: The spontaneous and random emission of particles from the nucleus of an atom. There are 3 types α 2 protons and 2 neutrons β 1 electron γ photon 217 At 213 Bi ? Pa 234 Bi ?

Atomic Physics In a nuclear reactor, is broken down by a chain of α and β particles 238 U 234 Th 9290 α particle 238 U 92

Atomic Physics 234 Th 234 Pa 9091 β particle

Atomic Physics 234 Pa 234 U 9192 β particle

Atomic Physics 234 U 230 Th 9290 α particle

Atomic Physics 230 Th 226 Ra 9088 α particle

Atomic Physics 226 Ra 222 Rn 8886 α particle

Atomic Physics 218 Po 84 then loses an α particle, then β, α, β, β, β then α What does it end up as? 206 Pb 82

Atomic Physics Deflection by a Magnetic Field α – particle deflected slightly because it has the greatest mass β – particle deflected more because it has less mass and in the opposite direction as it has the opposite charge γ – radiation, no deflection because it has no charge and no mass

Atomic Physics  The radio active source is not a health risk as α – particles can travel only a short distance in air. As they are placed on the ceiling, they are well away from people. Smoke Detector The radioactive source emits α – particles that ionise the air, ie, they remove electrons forming positive and negative ions. This allows the current to flow. Smoke particles absorb the α – particles so the ionisation stops. The current stops that triggers the alarm

Atomic Physics Calculating the Energy Released in a Nuclear Reaction 2 H H 1 4 He n 0 +energy The amount of energy released is given by the formula E = mc 2 Where mass is the mass that has been “lost”, and c is the speed of light, 3.00 x 10 8 ms -1 The mass of the nucleus of: Deuterium is x kg Tritium is x kg Helium is x kg A neutron has a mass of x kg Find the energy released in this reaction

Deuterium x Helium x Tritium x Neutron x Total x Total x x x Difference x Atomic Physics Energy released = x kg x (3.00 x 10 8 ms -1 ) 2 = x J

Atomic Physics + β particle 228 Ra 228 Ac 8889 The mass of the Radon nucleus is x kg The mass of the Actium nucleus is x kg The mass of a β particle is x kg The energy released is x J