Physics - P4 - Atomic Structure

Question	Answer
Describe the Greek model of the atom in eight words.	Tiny spheres called atoms which were indivisible.
Democritus originally came up with which model of the atom?	The Greek model
John Dalton agreed with the Greek model but theorised that each element had: (the same/a different) atom.	A different atom.
Who was credited with discovering electrons?	J J Thompson
What model of the atom did J J Thompson theorise?	Plum pudding model.
Who came up with the first nuclear model?	Ernst Rutherford
What experiment did Rutherford use to discover the first nuclear model?	Alpha scattering experiment.
What results were expected from the alpha scattering experiment and why were they expected?	The expected results were that particles would pass through or for a select few be deflected because of the plum pudding model.
How does the prediction of the alpha scattering experiment compare to the results?	They expected particles to pass through or be deflected and they passed through but some deflected more than expected.
What did the results of the alpha scattering experiment prove?	1) Mass was concentrated in the centre. 2) The nucleus had a + charge. 3) Most of the atom was empty space.
Niels Bohr suggested that orbiting electrons do so at different distances called what?	Energy levels.
James Chadwick proved the existence of which sub atomic particle and what did it help to explain?	Proved existence of neutron to explain the imbalance between the atomic and mass numbers.
The nucleus contains which two sub atomic particles?	Protons and neutrons.
What charges does each sub atomic particle in a nucleus have and what is the overall charge of a nucleus?	Proton: +1 Neutron: 0 Nucleus: +
The radius of the nucleus is about (100/1,000/10,000) times smaller than the radius of the whole atom.	10,000
Most of an atom is comprised of mostly what?	Empty space.
What sub atomic particles orbit the nucleus and what charge do they have?	Electrons with -1 charge.
The number of protons is equal to the number of what? Why is this?	Electrons This is because the charges then even out. + and - charges cancel out.
What are isotopes?	Isotopes are different forms of the same element.
All isotopes have the same number of which sub atomic particle?	Protons
The number of protons defines the atomic _____ of an element.	Number
The mass number of an atom is the sum of the total of which sub atomic particles?	Protons and neutrons.
Isotopes have differing numbers of which sub atomic particle?	Neutrons.
How many elements have isotopes?	All of them! hOW maNy Of thOsE aRe sTable? It's a code. Figure it out!
What happens to the unstable isotopes and why do they do this?	They decay into other elements and emit radiation as they try to become more stable
What is radioactive decay and why does it happen?	Radioactive decay is when isotopes emit radiation while balancing the sub atomic particles to become more stable.
What are the three main types of radiation?	Alpha Beta Gamma
Alpha particles are what type of nuclei and why is this?	They are helium nuclei as the alpha particles have two protons and two neutrons.
How penetrating is alpha radiation?	Low
How far does alpha radiation travel?	Around 3-5 cm. Basically just a few cm.
What is alpha radiation stopped by?	A sheet of paper.
How ionising are they?	Very ionising.
Put the types of radiation in terms of ionisation. Starting with the highest.	Alpha Beta Gamma
Put the types of radiation in order of distance travelled. Starting with the highest.	Gamma Beta Alpha
What is beta radiation?	A fast moving electron.
What is gamma radiation?	An electromagnetic wave.
Nuclear equations show radioactive _____ by using element symbols.	Decay
How are nuclear equations written?	atom before decay ---> atom after decay + radiation emitted.
What is the golden rule when writing nuclear equations?	The total mass and atomic numbers must BE THE SAME!
Alpha decay __________ the charge and mass of the nucleus.	Decreases.
Why does the mass and charge decrease when alpha decay occurs?	Because a helium nuclei is released during alpha decay.
When alpha decay occurs, how much is the atomic number and mass number reduced by?	Atomic: 2 Mass: 4 Why do you think this is?
Why is the charge reduced during alpha decay?	Because protons are being removed from the isotope. Protons are + charged therefore you are left with a negative charge.
Uranium 238 becomes Thorium 234 during alpha decay. Write a nuclear equation to show this.	238 ---> 234 + 4 92 ---> 90 + 4 U ---> Th + He
Beta decay increases the _____ of the nucleus.	Charge
Why does beta decay increase the charge of a nucleus?	Because the process involves losing an electron so as a result the charge increases as electrons have a negative charge.
Does the mass or charge change during gamma decay? Why or why not?	No because there is no change to atomic mass or number because gamma decay just removes excess energy.
Radioactivity is a (controlled/random) process.	Random
What is half life?	Half life is the amount of time needed for the radiation emitted to half. (Also called the amount of activity)
What is half life measured in?	Becquerels Bq
The radioactivity of a source _________ over time.	Decreases
When does the activity of a radioactive source reach zero?	It never does.
The initial activity of a sample is 640Bq. Calculate the final activity as a percentage of the initial activity after 2 half lives.	25%
How can you measure the half life using a graph?	Find the time interval corresponding to the activity twice and then find the difference of the time intervals.

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