Flashcards
P4 - Atomic Structure/radioactive decay
Cards in this deck (12)
- 1Atomic StructureCharge
Proton - 1+
Neutron - 0
Electron - 1-
Mass
Proton - 1
Neutron - 1
Electron - 1/2000
location
proton - in the nucleus
neutron - in the nucleus
electrons - in the shells - 2Radioactive DecayAn atom’s nucleus can only be stable if it has a certain amount of neutrons for the amount of protons it has.
- 3Radioactive Decay 2An unstable nucleus can decay by emitting an alpha particle, a beta particle, a gamma ray or in some cases a single neutron.
- 4Alpha ParticleAlpha decay causes the mass number of the nucleus to decrease by four and the atomic number of the nucleus to decrease by two. Helium nucleus charge of 2+ least penetrating damage DNA.
- 5Beta ParticleIf the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron. This electron is called a beta ( β ) particle – this process is known as beta radiation. Relative mass of 0.
- 6Gamma ParticleHigh energy particles will emit energy as they drop to lower energy levels. Since energy levels in the nucleus are much higher than those in the gas, the nucleus will cool down by emitting a more energetic electromagnetic wave called a gamma ray. Most penetrating.
- 7Stable nucleiAn atom’s nucleus can only be stable if it has a certain amount of neutrons for the amount of protons it has.
Elements with fewer protons, such as the ones near the top of the periodic table, are stable if they have the same number of neutrons and protons. For example carbon, carbon-12 is stable and has six protons and six neutrons.
However as the number of protons increases, more neutrons are needed to keep the nucleus stable. For example lead, lead-206 has 82 protons and has 124 neutrons. - 8Neutron emissionOccasionally it is possible for a neutron to be emitted by radioactive decay. This can occur naturally, ie absorption of cosmic rays high up in the atmosphere can result in neutron emission, although this is rare at the Earth’s surface. Or it can occur artificially, ie the work done by James Chadwick firing alpha particles at Beryllium resulted in neutrons being emitted from that.
A further example of neutron emission is in nuclear fission reactions, where neutrons are released from the parent nucleus as it splits.
Neutron emission causes the mass number of the nucleus to decrease by one and the atomic number remains the same. - 9Properties of nuclear radiationsThe different types of radiation are often compared in terms of their penetrating power, their ionising power and how far they can travel in the air.
- 10Half lifeRadioactive decay is a random process. A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time so it is impossible to tell when a particular nucleus will decay.
It is not possible to say which particular nucleus will decay next, but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Scientists cannot tell when a particular nucleus will decay, but they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed. This is called the half-life. - 11Calculating the isotope remaininga fraction - a ½ of a ½ of a ½ of a ½ remains, which is ½ × ½ × ½ × ½ = 1/16 of the original sample
a decimal – 1/16 = 0.0625 of the original sample
a ratio – given in the form 'activity after n half-lives : initial activity' , in this case 1:16 - 12Nuclear equationsA nucleus changes into a new element by emitting alpha or beta particles. These changes are described using nuclear equations.
Alpha decay (two protons and two neutrons) changes the mass number of the element by -4 and the atomic number by -2. An alpha particle is the same as a helium-4 nucleus.
Beta decay changes the atomic number by +1 (the nucleus gains a proton) but the mass number remains unchanged (it gains a proton but loses a neutron by ejecting an electron, so a beta particle is an electron).
Gamma is pure energy and will not change the structure of the nucleus in any way.
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- Flashcards on P4 - Atomic Structure/radioactive decay, created by Charlie Seymour on 12/06/2019.
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- Charlie Seymour
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- Created by Cam Hodges · Jan 9, 2019
- Copied by Toby Crawford · Jan 10, 2019
- Copied by Charlie Seymour · Jun 12, 2019
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