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?
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 unit is activity measured in?
Activity is measured in Becquerels (Bq). An activity of 1 Bq means one decay 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).