Atomic Structure Flashcards
What happens in an atom when electromagnetic radiation is absorbed?
An electron moves into a higher energy level (further away from the nucleus).
How many times bigger is the radius if the atom than the radius of the nucleus?
More 10000.
Where is most of the mass concentrated in an atom?
Nucleus
What are isotopes?
Atoms of the same element that have different numbers of neutrons.
Describe Thomson’s Plum Pudding Model.
- Mass and positive charge are spread evenly throughout the atom.
- Negatively charged electrons are embedded within the atom.
Describe Rutherford’s Nuclear Model.
- All the positive charge and most of the atom’s mass concentrated within a tiny central nucleus.
- Except for orbiting electrons, the atom is mostly empty space.
Describe how the alpha particle scattering experiment led to the replacement of the plum pudding model by the nuclear model.
All of the fast moving positively charged alpha particles would have passed straight through the gold foil of the plum pudding model was correct. Some alpha particles were deflected and a few were repelled straight back. This led to the nuclear model idea that atomic mass is concentrated in a positively charged centre.
Describe the Bohr model.
Electrons are organised into energy levels at specific distances from the nucleus.
What did Chadwick discover?
The neutron.
What is radioactive decay?
A random process that happens when an unstable atomic nucleus gives out nuclear radiation to become more stable.
What is activity?
The rate at which a source of unstable nuclei decays. It is measured in becquerel (Bq).
What is count rate?
The number of decays recorded each second by a detector.
Alpha Particle:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power
- A helium nucleus
- < 5cm
- loses 2 protons and 2 neutrons
- Paper/skin
- Most strongly ionising
Beta Particle:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power
- High speed electron
- 1 metre
- A neutron turns into a proton
- 5mm of Aluminium
- Low
Gamma Ray:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power
- High frequency electromagnetic radiation
- Infinite
- No change
- Lead
- Very low
What is ionising power?
The ability of the radiation to change an uncharged atom into a charged one.
What are the two ways that nuclear radiation can be detected and measured.
A Geiger-Muller tube measures the count-rate when connected to a rate-metre.
Photographic Film turns foggy into the presence of radiation.
How is an alpha particle shown as in a nuclear equation?
4
He
2
How is a beta particle shown in a nuclear equation?
0
e
-1
Why does the emission of a gamma ray not cause the mass or the charge of the nucleus to change?
Gamma rays are electromagnetic radiation so have no mass and no charge.
What is half-life?
- The time it takes for the number of nuclei of the unstable isotope in a sample to halve
- The time it takes for the count rate, or activity, of a sample to halve.
Radioactive isotopes with longer half-lives are described as having …
More stable nuclei.
What is net decline expressed as a ratio?
Activity after n half-lives : initial activity
Where n represents a number of half-lives.
What is contamination?
The presence of materials containing radioactive atoms on or in other materials.
