P4 Atomic structure Flashcards
How big is an atom?
An atom has a radius of about 1 x 10-10 m.
Describe the basic structire of an atom?
An atom is made up of a positively charged nucleus (containing protons and neutrons) surrounded by negatively charged electrons.
How big is the nucleus compared to the atom?
The nucleus is about 1/10000 the size of the atom.
If the atom was as big as the moon, the nucleus would be the size of a penny!
Where would you find most of the mass of the atom?
Most of the mass of the atom is in the nucleus.
Electrons are arranged in energy levels around the atom.
How is it possible for the electrons to move from one energy level to another?
Electrons may move further from the nucleus (a higher energy level) if they absorb electromagnetic radiation such as light.
They may move closer to the nucleus (a lower energy level) by emitting (giving out) electromagnetic radiation such as light.
What’s the overall charge on an atom?
An atom is neutral. It has the same number of protons (+) as electrons (-).
What charge do protons have?
Protons are positive.
What charge do neutrons have?
Neutrons are neutral.
What charge do electrons have?
Electrons are negative.
All atoms of the same element must have the same number of what?
All atoms of the same element must have the same number of protons. This is what determines the element.
For example, anything that has 6 protons is always carbon. If it has 7, it must be nitrogen.
What does the atomic number represent?
The atomic number is the number of protons in an atom. For this reason, it is sometimes called the proton number.
What is the mass number?
The mass number is the number of protons plus neutrons.
How would you work out the number of neutrons in an atom if you were given the atomic number and the mass number?
The number of neutrons equals the mass number (protons + neutrons) minus the atomic number (number of protons).
What is meant by an isotope?
Isotopes are atoms of the same element that have different numbers of neutrons.
If an atom loses an outer electron, what does it become?
An atom that loses an outer electron becomes a positive ion.
How many protons, neutrons and electrons are there in this isotope of carbon?
6 protons
6 electrons
8 neutrons
What leads to scientific ideas or models being changed or replaced?
New evidence leads to scientific ideas or models being changed or replaced.
The discovery of which particle led to the plum pudding model of the atom?
The discovery of the electron led to the plum pudding model of the atom.
Describe the plum pudding model of the atom.
The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.
Which experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged.
The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged.
Which model of the atom replaced the plum pudding model?
The nuclear model of the model replaced the plum pudding model.
What were the results of the alpha particle scattering experiment?
Most alpha particles went straight through the gold foil (most of the atom is empty space).
Some alpha particles were deflected (the positive charge is in the nucleus, and repels the alpha particles).
A few alpha particles bounced back (the mass is in the nucleus)
How did Niels Bohr adapt the nuclear model?
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
Whose experimental work provided the evidence
to show the existence of neutrons within the nucleus?
The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus.
Why do some nuclei give out radiation?
Some nuclei give out radiation because they are unstable. Giving out radiation makes them more stable.
What is radioactive decay?
Radioactive decay is a process where unstable atoms give out radiation to become more stable. This is a random process.
What is meant by the ‘activity’ of a radioactive substance?
‘Activity’ is measurement of the rate of decay of a radioactive material. Literally, how many atoms decay (give out radiation) per second.
What’s a Geiger-Muller tube?
A Geiger-Muller tube is a detector used to detect radiation. It is sometimes called a Geiger counter.
What is meant by ‘count-rate’?
Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).
Name 3 types of radiation that might be emitted from a radioactive material.
3 types of radiation that might be emitted from a radioactive material are:
What does an alpha particle consist of?
An alpha particle (α) consists of two neutrons and two protons, it is the same as a helium nucleus.
What does a beta particle consist of?
A beta particle (β) is a high speed electron ejected from the nucleus as a neutron turns into a proton.
What is a gamma ray?
Gamma (γ) is high frequency electromagnetic radiation from the nucleus.
What can stop alpha particles?
Alpha can be stopped by a sheet of paper.
What can stop beta particles?
Beta can be stopped by a a few mm of aluminium.
What can stop gamma rays?
Gamma can be stopped by a few cm of lead or a few m of concrete.
What symbol can be used to represent an alpha particle in an equation?
An alpha particle can be represented by this symbol, because it is the same as the nucleus of a helium atom.
What symbol can be used to represent a beta particle in an equation?
A beta particle can be represented by this symbol, because it is the same as an electron.
An alpha decay can be shown by this equation, where uranium decays into thorium.
What would be the atomic number and the mass number of this thorium isotope?
The uranium has given out an alpha particle so it has lost 2 protons and 2 neutrons. The mass number therefore goes down by 4 and the atomic (proton) number by 2.
A beta decay can be shown by this equation, where carbon decays into nitrogen.
What would be the atomic number and the mass number of this nitrogen isotope?
The carbon has given out a beta particle so it has lost a neutron and gained a proton. The mass number therefore stays the same and the proton number goes up by one.
What is the half life of this isotope?
The half life is 2 days.
Read off the graph the time taken for the activity (counts per minute) to halve from 80 to 40.
You can cjheck this by seeing how long it takes to halve from 40 to 20, which will also be 2 days.
What is meant by radioactive contamination?
Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials.
Why is radioactive contamination a hazard?
The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation (alpha beta or gamma) emitted affects the level of hazard.
