Combined Physics - 6.4
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What is the size of an atom?
Very small – a radius of about 1x10-10 m
Describe the basic structure of an atom
A positively charged nucleus (protons and neutrons) orbited by negatively charged electrons
What is the radius of the nucleus
1/10’000th the radius of an atom (but contains most of the mass)
Describe electrons within energy levels
Electrons are arranged at different distances (energy levels) from the nucleus
How can electron arrangements change?
• Absorption of electromagnetic radiation (higher energy level) • Emission of electromagnetic radiation (lower energy level)
What is the overall electrical charge of an atom?
No overall charge – electron and proton numbers are equal
How many protons do an atom of the same element have?
The same number
What is the atomic number?
The number of protons in an atom
What is the mass number?
The number of protons and neutrons in an atom
Draw the modern model of an atom
What is an isotope?
Atoms of the same element with different numbers of neutrons
What happens to an atom if it loses one or more outer electron(s)?
It becomes a positive ion
Before the discovery of the electron, what were atoms thought to be (as suggested by Dalton)?
Tiny spheres that could not be divided
What was the Plum Pudding model?
The atom was suggested to be a ball of positive charge with negative electrons embedded in it
What did Rutherford’s scattering experiment show?
The mass of the atom was concentrated in the centre (nucleus) and it was charged
How did Bohr adapt the nuclear model as suggested by Rutherford?
Bohr suggested electron orbit the nucleus at specific distances (energy levels)
What can the positive charge of a nucleus be subdivided into?
Protons
20 years after the nucleus became scientifically accepted, what did James Chadwick identify?
Neutrons (explaining the imbalance between atomic number and atomic mass)
Some atomic nuclei are unstable – what can the nucleus emit (and in doing so become more stable)?
Radiation – a random process of radioactive decay of the unstable nuclei
What is ‘activity’ in terms of nuclear radiation?
The rate at which a source of unstable nuclei decays
How is nuclear ‘activity’ measured?
In becquerels (Bq) where 1 Bq is 1 decay per second
What can a Geiger-Muller tube record?
The count-rate (the number of radiation decays reaching the device per second)
What types of ionising nuclear radiation are there?
• Alpha • Beta • Gama
Describe alpha (α) radiation (structure, penetration, absorption and ionising strength)
• 2 neutrons and 2 protons (like a helium nucleus) • They don’t penetrate very far (a few cm in air) and are absorbed by a piece of paper • They are strongly ionising