Unit 4 - Atomic Structure Flashcards
State why the nuclei of certain atoms/isotopes are unstable
The nuclei of certain atoms/isotopes are unstable due to the number of protons and nucleus in the nucleus of an atom
What do radioactive isotopes do
Some isotopes are radioactive. What does this mean.
(it means that)Their nuclei decay and release radiation
What is radioactive decay
Radioactive decay is the random process of a radioactive substance giving out radiation from the nuclei of its atoms.
Some isotopes/certain atoms have an _______
Some isotopes/certain atoms have an unstable nucleus
What must the nuclei of atoms do to become stable
To become stable the nucleus must release radiation (decay - radioactive decay) in the form of a particle or as an electromagnetic wave
Radioactive decay is a totally ______ process
Radioactive decay is a totally random process
What is activity
The activity is the rate at which a source of unstable nuclei decay.
Activity is measured in _____
units of activity
Activity is measured in becquerel (Bq)
Activity is measured in _____
Activity is measured in becquerel (Bq)
1 Bq =
1Bq = 1 decay per second
What is a Geiger-Muller tube used for
To measure the activity of a radioactive source we can use a Geiger-Muller tube
What is count rate
Count-rate is the number of decays recorded each second by a detector (such as: Geiger-Muller tube)
How is count rate different to activity
It must be remembered that the count recorded by the G-M tube will be caused by the radiation from the source plus that due to background radiation.
The activity is the rate at which a source of unstable nuclei decay.
When it comes to atoms emitting radiation what can and cant we predict
We cannot predict when an atom will give out radiation
We can predict what percentage of the atoms will give out radiation
can’t predict which nucleus will
decay next
or
can’t predict when a (particular)
nucleus will decay
What is ionising radiation
Radiation that has enough energy to knock of electrons off atoms (to become an ion)
Radiation hits an atom and caused the atom to become an ion - loses/gains electrons
When it comes to radiation what is random and what can we predict
The process of emitting radiation is completely random
We can predict what percentage of the atoms will give out radiation
Who discovered the electron
J.J. Thomson
Who developed the plum pudding model (of the atom)
J.J. Thomson
describe the the alpha scattering experiment
A beam of alpha particles was aimed at very thin gold foil and their passage through the foil was detected.
why was the alpha scattering experiment done
Scientists (Rutherford) wanted to know if the plum pudding model was correct, and to find this out they carried out an experiment
What did J.J. Thomson do
He discovered the electron, and he then developed the Plum Pudding Model (of the atom)
The discovery of the electron led to what?
The discovery of the electron led to the plum pudding model of the
atom
Describe the plum pudding model
The Plum Pudding Model is a ball of positively charged matter containing negative electrons
Draw the plum pudding model
https://images.twinkl.co.uk/tr/image/upload/t_illustration/illustation/Plum-Pudding-Model—Science-Diagram-KS4.png
Scientists knew that atoms contained electrons and that electrons had a negative charge
They also knew that an atom was electrically neutral overall
What did this allow the scientists to deduce about the pudding part of the atom
The pudding part of the atom had a positive charge - it has an equal amount of positive charge as there are negative charge
Who did the Alpha-particle scattering experiment
Ernest Rutherford
What model of atom was the plum pudding model replaced with
The nuclear model
State the results obtained by Mr Rutherford for the Alpha-particle scattering experiment
Most alpha particles went straight through the gold foil without causing damage
Some alpha particles ere deflected through small angles
About 1 in 8000 of the alpha particles were reflected straight back
Using the nuclear model of the atom explain why the alpha particles went in those directions
Most of the atom is empty space therefore the alpha particles could pass through
The atom contained a nucleus which was positively charged which deflected the alpha particles
Most of the mass of the atom was concentrated in the positively charged nucleus, which caused the alpha particles to be reflected straight back
Using the nuclear model, Rutherford devised an equation to predict the proportion of alpha particles that would be deflected though various angles
The results of the experiment were the same as the predictions made by Rutherford
What was the importance of the experimental results and the predictions being the same
The experimental results proved the predictions were correct
Why did the Alpha particle scattering experiment lead to a new model of the atom, called the nuclear model, replacing the ‘plum pudding’ model
The results of the experiment could not be explained by the plum pudding model therefore a new model had to be produced
the difference between the plum pudding model of the atom
and the nuclear model of the atom
The Plum Pudding Model is a ball of positively charged matter containing negative electrons
the nuclear atom there is a tiny, dense positively charged nucleus at the centre, where most of the mass is concentrated. A cloud of negative electrons surrounds this nucleus - so most of the atom is empty space
___________
while the nuclear model has electrons that are orbiting around this nucleus (centre of the atom), which contains very dense positively charged protons
When was:
the proton, neutron discovered
Proton - 1917
Neutron - 1932
What were atoms thought to be before the discovery of the electorn
Before the discovery of the electron, atoms were thought to be tiny
spheres that could not be divided.
Describe how the proton and neutron were discovered
Later experiments led to the idea that the positive charge of any
nucleus could be subdivided into a whole number of smaller
particles, each particle having the same amount of positive charge.
The name proton was given to these particles.
The experimental work of
James Chadwick provided the evidence
to show the existence of neutrons within the nucleus.
What did Niels Bohr say in 1913
In 1913, Niels Bohr said that electrons orbit at different (/specific) distances from the nucleus
Bohr’s work agreed with the results of experiments by other scientists (so it was accepted)
These orbits are called energy levels/shells
What is the size of radius of an atom
Atoms are very small, having a radius of about 1 × 10-10 metres.
Describe the structure of an atom
The atom has a positively charged nucleus.
The nucleus has positively charged protons and neutrons which have got no charge.
The nucleus is surrounded by negatively charged electrons
The electrons are arranged at different distances from the nucleus
(different energy levels).
What is the size of the radius of an nucleus
The radius of a nucleus is less than 1/10 000 of the radius of an atom
How are the electrons in the nucleus arranged
The electrons are arranged at different distances from the nucleus
(different energy levels).
How might electron arrangement change when radiation is absorbed or emitted
If the atom absorbs
(electromagnetic) radiation an electron can move from a lower energy level to a higher energy level (the atom can now emit electromagnetic radiation and the electron returns back to the lower energy level)
If the atom emits radiation an electron can move from a higher energy level to a lower energy level
how is an alpha particle different from a helium atom
An alpha particle has 2 protons and 2 neutrons whereas a helium atom has 2 protons, 2 neutrons and 2 electrons.
State the four types of radiation
Alpha
Beta
Gamma
Neutron
Types of nuclear radiation
An alpha particle (α)
A beta particle (β)
A gamma ray (γ)
A neutron (n)
https://banner2.cleanpng.com/20180723/qby/kisspng-gamma-ray-symbol-ionizing-radiation-5b5563c7659891.2656795115323227594162.jpg
What is an alpha particle
A particle which consists of two protons and two neutrons (IT IS THE SAME AS A HELIUM NUCLEUS)
State the charge of an alpha particle
+2
penetrating power
Tells us what type of material is required to stop each form of radiation
what is ionising power
When radiation collides with atoms, that can cause the atoms to lose electrons and form ions
Very strongly ionising means that the radiation can produce a lot of ions when they collide with a material
What can stop alpha radiation (penetrating power)
Alpha particles can be stopped by
5cm of air
A single sheet of paper
Top layer of skin
Alpha particle’s range in air
Alpha particles are large. They can travel around 5cm in air before they collide with air particles and stop
Describe the ionisation ability (ionising power) of an alpha particle
Very Strongly ionising
Are alpha particles affected by electric and magnetic fields
Yes
How is an atom neutral
An atom contains the same number of positively charged protons as negatively charged electrons
(the negative charges on the electrons cancel out the positive charges on the protons, making the overall atom neutral)
Is an alpha particle dangerous
Outside the body - No
Inside the body - very dangerous
What is a beta particle
A beta particle is a high speed electron ejected from the nucleus as a neutron turns into a proton
A beta particle is an electron that originates from the nucleus
Beta particle’s range in air
Beta particles range in air about 1m before stopping
How is a beta particle formed (since nucleus of atoms do not contain electrons)
A beta particle is formed inside the nucleus when a neutron changes into a proton and an electron
The electron is ejected from the nucleus. This electron is called a beta particle
What stops a beta particle (penetrating power)
3mm of Aluminium
harder to stop than alpha particle
State the ionisation ability of a beta particle
moderately/quite strongly ionising (not as ionising as alpha particles - since they are smaller)
___________
Very weak (since it is smaller)
Are beta particles affected by electric and magnetic fields
Yes (any charged particle is affected)
Are beta particles dangerous
Yes - but it is more dangerous outside the body than inside the body
What is a gamma ray
A gamma ray is a very high energy electromagnetic wave, originating from the nucleus
Gama radiation range in air
Gamma radiaiton travels several metres in air before stopping
(unlimited - spreads out in air without being absorbed - aqa textbook)
What can stop a gamma ray (penetrating power)
Nothing
But, thick lead and concrete can reduce its intensity
_______________
several centimetres of lead
metres of concrete (more than 1m thick)
Ionisation ability of a gamma ray (ionising power)
Very weak
weakly ionising
Is it affected by electric and magnetic fields
No
Are gamma rays dangerous
Yes but it is more dangerous outside the body than inside the body
Draw the symbol for an alpha particle, beta particle and a gamma ray
α - alpha
β - beta
https://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Latin_letter_small_capital_Gamma.svg/2185px-Latin_letter_small_capital_Gamma.svg.png - gamma
