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The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)
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P2 7.1 Nuclear reactions
Some atoms have an unstable nucleus and need to get to a lower energy state.
It can become stable by emittingAlpha, Beta or gamma radiation. It “decays”.
The structure of the atom
ELECTRON – negative,
mass nearly nothing
PROTON – positive,
same mass as neutron
(“1”)
NEUTRON – neutral,
same mass as proton
(“1”)
The structure of the atom
-10Electron01Neutron11Proton
Relative ChargeRelative MassParticle
MASS NUMBER = number of protons + number of neutrons
PROTON NUMBER = number of protons (obviously)
IsotopesAn isotope is an atom with a different number of neutrons:
Each isotope of oxygen has 8 protons
The mass number is different. How many neutrons does each isotope have?
ISOTOPES OF CARBON
C14
6C13
6C12
6
ISOTOPES OF CARBON
C14
6C13
6C12
6
Q1. How many protons does each carbon atom have? Q2. How many electrons does each carbon atom have?Q3 How many neutrons does each carbon atom have?
ISOTOPES OF CARBON
C14
6C13
6C12
6
Q1. How many protons does each carbon atom have? 6 Q2. How many electrons does each carbon atom have?Q3 How many neutrons does each carbon atom have?
ISOTOPES OF CARBON
C14
6C13
6C12
6
Q1. How many protons does each carbon atom have? 6 Q2. How many electrons does each carbon atom have? 6 Q3 How many neutrons does each carbon atom have?
ISOTOPES OF CARBON
C14
6C13
6C12
6
Q1. How many protons does each carbon atom have? 6 Q2. How many electrons does each carbon atom have? 6 Q3 How many neutrons does each carbon atom have? 6, 7, 8
Radioactivity
Isotopes of the same element always have the same number of in their nuclei, but they can have different numbers of .
electrons ? protons ? neutrons?
Carbon isotopes:
eg carbon 12 carbon 14
12 14 6 protons & 8 neutrons
6 6 proton number
C
C
Some isotopes have unstable . Without warning the breaks up releasing , or radiation and possibly forms a new element. (nucleus, , , atoms)
Types of radiation
1) Alpha () – a nucleus decays into a new nucleus and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)
Unstable nucleus
New nucleus
Alpha particle
decay:
200 196 4
100 98 2+D HeP
Types of radiation
1) Alpha () – a nucleus decays into a new nucleus and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)
Unstable nucleus
New nucleus
Alpha particle
Eg 1:
228 ... 4
90 ... 2He+Th Ra
decay:
200 196 4
100 98 2+D HeP
Types of radiation
1) Alpha () – a nucleus decays into a new nucleus and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)
Unstable nucleus
New nucleus
Alpha particle
decay:
200 196 4
100 98 2+D HeP
Eg 1:
228 4
90 2He+Th Ra
22488
2) Beta () – a nucleus decays into a new nucleus by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.Unstable
nucleusNew
nucleus
Beta particle
Types of radiation
decay:
200 200 0
100 101 -1+P D
2) Beta () – a nucleus decays into a new nucleus by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.Unstable
nucleusNew
nucleus
Beta particle
Types of radiation
decay:
200 200 0
100 101 -1+P D
Eg 2:
40 ... 0
19 ... -1+K Ca
2) Beta () – a nucleus decays into a new nucleus by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.Unstable
nucleusNew
nucleus
Beta particle
Types of radiation
decay:
200 200 0
100 101 -1+P D
Eg 2:
40 0
19 -1+K Ca
4020
Types of radiation
1) Alpha () – a nucleus decays into a new nucleus and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)2) Beta () – a nucleus decays into a new nucleus by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.
Unstable nucleus
Unstable nucleus
New nucleus
New nucleus
Alpha particle
Beta particle
3) Gamma – after or decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The nucleus is not changed.
Unstable nucleus
New nucleus
Gamma radiation
Background radiation
This is ionising radiation from:
cosmic rays (from outer space) 13 %X ray tubes 21%radon gas from granite rocks 16%food and drink 16%air 33%nuclear reactors leaking 0.1%nuclear weapons testing 0.4%
Ionisation is the removal of an electron from an atom leaving it as a positively charged ion
* random nature of radioactivity means that the readings (i.e. number ofcounts in three minutes) do vary and that the more readings made, thegreater the reliability.
Experiment to measure Background count rate /min:
27p 33n
