P7-Atomic Structure Flashcards
What are alpha particles and whats their numbers
4
He
2
What are the numbers for beta
0
B
-1
What are the numbers for gamma and what are gamma waves
0
Electro magnetic waves
0
What can stop alpha particles
Piece of paper
What can stop beta particles
Few sheets of alluminium
What can stop gamma waves
Several cm of led
How far so alpha particles travel
5cm
How far do beta particles travel
1m
How far do gamma particles travel
Unlimited distance
What happens to the activity of a source as more unstable atoms decay
Reactivity decreases
What is count-rate and what is used to measure it
The number of decays record each second by a geiger counter
What does it mean if theres a shorter half life in a radioactive dice graph
It is more reactive as less radioactive nuclei have decayed
How do you calculste the count rate after 3 half lives with a count rate of 60
60/2^3=7.5
Count rate before/2^half lives
What did john dalton discover and when did he discover it
That matter was made up of tiny spheres (atoms) that couldnt be broken upbyt thought each element was made up of different types of atms. 1804.
What did J J thompson discover and when did he discover it
- Plum pudding. JJ thompson discovere particles called electrons and that they could be removed from atoms, this proved dalton theory wrong. Atoms where spheres of positive charge with negative electrons stuck in them like a plum pudding.
What did rutherfood discover and when did he discover it. Who did he prove wrong.
In 1909. Scientists in rutherfoods lab fired a beam of alpha particles at thing gold foil (alpha scattering) experiments. From the plum pudding model, they expected the particles to pass straight through the gold sheet or only be slightly deflected. Although most did however some were deflected. Plum-pudding model couldnt explain this so J J Thompsons theory was peoven wrong.
How was the nucleus discovered
After scientists in rutherfoods lab fired alpha particles at thin gold foil and found some bounced back. This meant most of the mass of the atom must be concentrated at the centre in a nucleus. The nucleus also must have a positive charge as it would repell the positive charged alpha particles. Also because most of the alpha particles passed straight through the atom it meant most of the atom is just empty space.
What did Bohr discover
Bohr spdiscovered that electrons orbiting the nucleus do so at certain distances called energy levels.
What did chadwick discover and when did he discover it?
In 1932 chadwick proved the existance of the neutron explaining the imbalance between the atomic and mass numbers
What is the atomic number
The number of protons in an atom
What is the mass number
The mass of the nucleus, protons + neutrons
What is an isotope
Atoms with the same number of protons (atomic number) but a different number of neutrons (mass number)
What is radioactive decay
When unstable isotopes decay into other elements giving out radiation trying to become more stable ( tryinng to balance number of protons and neutrons by getting rid of excess energy)
What are the three types of ionising radiation radioactive particles spit out
Alpha
Beta
Gamma
What is ionising radiation
Radiation that knocks electrons off atoms creating positive ions
What are alpha particles
Helium nuclei
Give 3 characteristics of alpha particles
Dont penetrate far into materials and stopped quickly and are absorbed by paper
Can only travel a few cm
Strongly ionising
What are beta particles
Fast moving electron released by the nucleus
What happens when a beta particle is emitted
A neutron in the nucleus turns into a proton
What are gamma rays
Waves of electromagnetic radiation released by the nucleus
Explain the leval of ionising gamma rays are
Weekly ionising because they usually pass through rather than collide with atoms
How are nuclear equations written
Atom before decay->atom after decay + radiation emitted
What is a key rule about nuclear equations
The total mass and atomic numbers must be equal on both sides of the equation
What happens to an atoms atomic number when it emits an alpha particle
The atomic number of the atom reduces by 2 and the mass number reduces by 4
How does alpha decay affect the charge and mass of the nucleus. Explain
The two positively charged protons that alpha particles contain are removed from the atom decreasing the charge of the atom
How does beta decay Affect the charge of the nucleus of an atom. Explain
Beta decay increases the charge of the nucleus because a neutron in the nucleus turns into a proton
How does gamma rays effect the charge of the nucleus
Doesnt change the charge because gamma rays only gets rid of excess energy
What is radiation measure by
Geiger-muller counter
What is half-life
The time taken for the number of radioactive nuclei in an isotope to halve
What can half-life be used to find
The rate at which a source decays, its activity
How can ionising radiation be bad
Ionising radiation can enter living cells and ionise atoms with them. This can cause danage to the cells or kill them off completely (can cause cancer)
What are two common wyas of reducing effects of radiation
Keep sources upin lead-lined boxes
Standing behind barriers when using sources
What is irradiation
Exposure to radiation
What is contamination
Radioactive particles getting onto objets
Why are contaminated particles harmful
If contaminated particles get onto or into an object they may decau and release radiation which could cause harm
Why are beta and gamma particles more dangerous than alpha particles
Because beta and gamma particles can penetrate into the body however alpha particles cant
Why are beta particles less damaging inside the body compared to alpha particle
Beta particles are less damaging because rsdiation is absorbed over a wider area and some passes out of the body too as they have the lowst ionising power. Alpha sources however do all their damage in a very localised area.
