P7 Flashcards
How are the electrons in an atom arranged?
An atom’s electrons are arranged at different distances from the nucleus (different energy levels).
How did James Chadwick make a discovery?
He bombarded beryllium atoms with alpha particles which caused an unknown radiation. He interpreted this as being composed of particles with a neutral electrical charge and the around the mass of a proton.
How does an electron move to a higher energy level?
by absorbing electromagnetic radiation
How does an electron move to a lower energy level?
by emitting electromagnetic radiation
Name a substance used as a fuel in nuclear reactors
Uranium
Order in the most ionising: beta, gamma, alpha
Alpha, Beta, Gamma
Unit of radiation
Becquerels (Bq)
What are ions?
Ions are charged particles that form when an atom either loses or gains electrons
What charge is alpha radiation?
Alpha particles are positively charged
What did James Chadwick discover?
Neturons
What did they discover as a result of the alpha particle experiment?
1) The mass of an atom was concentrated in the tiny nucleus
2) This nucleus must have a positive charge, since it repelled the positive alpha particles
3) Most of an atom is just empty space
What does the Bohr Model show?
The Bohr Model 1913 showed that electrons move in orbits of fixed size and energy
What does the number of protons in an atom determine?
Which element it is
What happens for every beta particle emitted?
A neutron in the nucleus is turned into a proton
What is a beta particle?
A fast-moving electron released by the nucleus
What is a gamma ray?
Gamma rays are waves of electromagnetic radiation released by the nucleus in the form of excess energy.
What is alpha radiation most commonly used in today?
In smoke detectors - it ionises air particles causing a current to flow. If there is smoke in the air, it binds to the ions making the current stop and the alarm sound.
What is alpha radiation?
Alpha radiation is when an alpha particle is emitted from the nucleus. An alpha particle consists of 2 neutrons and 2 protons (helium nucleus)
What is an atom?
An atom is the smallest piece of an element that can exist.
What is an isotope?
An isotope is an element that has the same number of protons but a different number of neutrons
What is beta radiation used for?
Beta radiation is used to test the thickness of sheets of metal
What is half-life?
The time it takes for the number of nuclei or amount of radiation to halve
What is ionising radiation?
Ionising radiation is radiation that knocks electrons off atoms, creating positive ions
What is radioactive decay?
An unstable nucleus can become more stable over time by randomly emitting ionising radiation.
What is the atomic number?
Number of protons
What is the mass and charge of a beta particle?
Beta particles have virtually no mass and a charge of -1
What is the mass and charge of a gamma ray?
Gamma rays have no mass or charge
What is the mass number?
protons + neutrons
What is the most common isotope of hydrogen?
Protium (1 proton and 0 neutrons)
What is the overall charge of the nucleus of an atom?
Positive (+1)
What is the radius of an atom?
1 × 10 -10
What is the range and ionising power of a beta particle?
Beta particles are moderately ionising and can travel a few metres. They are absorbed by a sheet of aluminium (around 5mm thick).
What is the range and ionising power of a gamma ray?
Gamma rays can travel infinitely through air and are weakly ionising because they tend to pass through rather than collide with atoms. They can be absorbed by thick sheets of lead or concrete.
What is the range of an alpha particle?
They don’t penetrate very far into materials and are stopped quickly - they can only travel between 5-11 cm and are absorbed by a sheet of paper.
What really happened as a result of the gold foil experiment?
Most of the particles did go straight through but some were deflected more than expected and a few were deflected back the way they had come. The scientists realised that most of the mass must be concentrated in the nucleus.
What shape is the line on a decay curve for a radioactive substance?
Curve downwards
What was the expected outcome of the alpha scattering experiment?
They expected the particles to pass straight through the sheet, or only be slightly deflected.
What was the Gold Foil Experiment?
In 1909, scientists in Rutherford’s lab fired a beam of alpha particles at a sheet of thin gold foil.
What was the Plum Pudding Model?
It was a model created in 1897 by Thompson which showed how the electrons are embedded in a sea of positive charge.
What was the Rutherford Model?
The Rutherford Model of 1911 saw the atom as a miniature solar system, with electrons orbiting around a nucleus containing neutrons/protons and the nucleus occupying a very small part of the atom.
When are positive ions created?
When an atom loses electrons
When atoms absorb electromagnetic radiation, do electrons move closer/away to the nucleus?
away
Where is most of the mass found in an atom?
In the nucleus
Who discovered electrons?
JJ Thompson
Who discovered the nucleus?
Ernest Rutherford
Why are most atoms neutral?
Because they have the same amount of protons and electrons
