⭐️Topic SP6 - Radioactivity Flashcards
What is particle theory?
A model that helps explain the properties of solids, liquids and gases with particles represented as spheres
When do chemical reactions occur?
When different atoms in substances become joined in different ways
What did J.J Thomson’s experiments show?
Atoms contain much smaller subatomic particles called electrons that have a negative charge and hardly any mass
What does the plum pudding model by J.J Thomson show?
An atom made of positively charged material with negatively charged electrons
What did Ernest Rutherfords experiment test?
What would happen if positively charged subatomic particles (alpha particles) passed through gold foil
What did Rutherford’s experiment show?
That most alpha particles passed through the foil but some bounced back disproving the plum pudding model instead suggesting the atoms were mostly empty space with most of their mass in a tiny nucleus with a positive charge and electrons moving around the nucleus
What is the radius of a nucleus and what is the radius of an atom?
Nucleus = 1 x 10 to the power of -15
Atom = 1 x 10 to the power of -10
So the atom is 100,000 times bigger than the nucleus
What is the particles that make the nucleus called?
Nucleons which can be protons or neutrons
What is the relative charge and relative mass of each subatomic particle
Proton - relative charge= +1
Relative mass= 1
Neutron-relative charge= 0
Relative mass= 1
Electron-relative charge= -1
Relative mass= almost 0 (negligible)What is the atomic number?
Number of protons in an atom
What is the mass number?
The number of neutrons and protons in an atom. The number of neutrons can vary
What gives the nucleus it’s positive charge?
The protons as neutrons have no charge
Why are atoms always neutral
As protons = electrons
What is an isotope?
Two atoms of the same element with the same atomic number but a different mass number. They are atoms of the same element with different numbers of neutrons
Give an example of an isotope
Carbon can occur naturally as carbon -12 carbon -13 or carbon -14 but all still have an atomic number of 6 as the number of neutrons has changed
What can electrons in an atom only exist in?
Electron shells where each is at a different level
Why do neon atoms absorb energy transferred by electricity?
As the electrons jump to higher shells and fall back down again when they emit energy as electromagnetic radiation
What is an emission spectrum?
A spectrum of electromagnetic radiation emitted by a source where each colour is a different wavelength of light
What is significant about gases in terms of energy?
They can absorb energy transferred by em radiation like visible light
How did Niels Bohr amend Rutherford’s model?
By suggesting that electrons can only be in certain electron shells around the nucleus and can’t part way between two orbits
What happens when an atom gains so much energy?
One or more of its electrons can escape from the atom altogether making the atom an ion
What is ionising radiation?
Radiation that causes electrons to escape
What is background radiation?
Ionising radiation at a low level from space and naturally radioactive substances in the environment
What is radon gas produced by?
Rocks that contain small amounts of uranium
Give some sources of background radiation
Air, foods and building materials
How can radioactivity be detected?
Through photographic film which darkens as more radiation reaches it. It has to be developed to measure the dose
What are dosimeters?
Film badges people who work with radiation wear to check their exposure
What are the ways radiation can be measured?
Using a dosimeter and a Geiger muller tube
What is a Geiger muller tube?
Where radiation passes through the tube and ionises the gad inside it and allows a short pulse of current to flow. It can be connected to a counter, to count the pulses of current
What is the count rate of the GM tube?
The count rate is the number of clicks per second
What must scientists do when measuring the radioactivity of a source?
The background radiation by taking several readings and then finding the mean
What of the nucleus of a radioactive substance is unstable?
It can easily change or decay which means radiation is emitted causing energy loss from the nucleus and the atom to become more stable. Decay is a random process
What are the types of radiation
Beta particles, positions, gamma rays and alpha particles
What do alpha particles contain?
Two protons and two neutrons like a helium atom’s nucleus. They have a relative mass of 4 and have no electrons and so have a charge of +2 and can be written as α
What are beta particles?
High energy, high speed electrons that have a negligible relative mass and a charge of -1 and can be written as β⁻
What are positrons?
High energy, high speed particles with the same mass as electrons but a charge of +1. They can be written as β⁺
What are gamma rays?
High frequency em waves that travel at the speed of light and don’t have an electric charge
What can all ionising radiation do?
Penetrate
What does an alpha particles high relative mass and high speed emission mean?
They transfers a lot of energy and so are good at ionising atoms they encounter but they loose energy each tune they ionise so they have a short penetration distance
What particle is most ionising?
Alpha particles
Which particle is most penetrative?
Gamma rays
Describe alpha particles in terms of penetrating and ionising
They travel a few cm in air, they are very ionising but can be stopped by a sheet of paper
Describe beta β⁻ particles in terms of penetrating and ionising
Travel a few meters in air, are moderately ionising but can be stopped by 3mm thick aluminium
Describe gamma rays in terms of penetrating and ionising
Will travel a few km in air, weakly ionising but need thick lead or several meters of concrete to stop them
