4. Atomic Structure Flashcards
What is the approximation for the radius of an atom?
1x10⁻¹⁰ metres.
What are the three subatomic constituents of an atom?
- Proton 2. Neutron 3. Electron
Where is most of the mass of an atom concentrated?
In the nucleus.
What proportion of the total radius of an atom is the radius of the nucleus?
1/10000th
Describe the arrangement of protons
neutrons
What charge does the nucleus of an atom have? Why?
- Positive charge. - The nucleus contains protons (positive charge) and neutrons (no charge).
Give two ways that an atom’s electron arrangement can be changed.
- Absorbing electromagnetic radiation. 2. Emitting electromagnetic radiation.
How does an atom’s electron arrangement change when it absorbs EM radiation?
Electrons move further away from the nucleus (higher energy level).
How does an atom’s electron arrangement change when it emits EM radiation?
Electrons move closer to the nucleus (lower energy level).
How does the ratio of electrons to protons result in the atom having no overall charge?
The number of protons equals the number of electrons, and their charges cancel each other out.
What do all forms of the same element have in common?
They all have the same number of protons.
What is the atomic number?
The number of protons in an atom.
What is an atom’s mass number?
The total number of protons and neutrons in the atom.
What is an isotope?
An atom of an element that has a different number of neutrons but the same number of protons.
How do atoms turn into positive ions?
By losing one or more electrons.
What may lead to a scientific model being changed or replaced?
Discovery of new experimental evidence that doesn’t agree with the existing theory.
How did the plum-pudding model describe the atom?
A ball of positive charge with negatively charged electrons distributed evenly throughout.
Prior to the discovery of the electron
what was believed about the atom?
Which experiment led to the plum-pudding model being discarded?
Rutherford’s alpha-scattering experiment.
What is the currently accepted model of the atom?
The Bohr nuclear model.
What were the conclusions of Rutherford’s alpha-scattering experiment?
- Most of the mass is concentrated in the nucleus. 2. The nucleus is positively charged.
What reinforces a scientific theory?
When experimental results agree with theoretical predictions.
What did James Chadwick’s experiments prove?
The existence of neutrons.
Why do unstable nuclei give out radiation?
To become more stable by undergoing radioactive decay.
What is radioactive decay?
The process where an unstable nucleus emits radiation to become more stable.
Define the activity of an unstable nucleus.
The rate of decay of a source of unstable nuclei.
What is the unit of radioactive activity?
Becquerel (Bq).
What is count-rate?
The number of radioactive decays per second for a radioactive source.
Give an example of a detector used to measure count-rate.
Geiger-Muller tube.
What are the four types of nuclear radiation?
- Alpha particles 2. Beta particles 3. Gamma rays 4. Neutrons
What are the constituents of an alpha particle?
Two protons and two neutrons (same as a helium nucleus).
What is the range of an alpha particle through air?
A few centimetres (typically 2-10 cm).
What will stop beta radiation?
A thin sheet of aluminium or several metres of air.
What will stop gamma radiation?
Several centimetres of lead or a few metres of concrete.
Which type of radiation is most ionising?
Alpha radiation.
Which type of radiation is least ionising?
Gamma radiation.
State any changes to mass or charge due to emission of a gamma ray.
Both mass and charge remain unchanged.
Describe the nature of radioactive decay.
- Random. - Which nucleus decays and when is determined by chance.
Define the half-life of a radioactive isotope.
- The time it takes for the number of unstable nuclei in a substance to halve. 2. The time it takes for the count rate to halve.
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials.
What is irradiation?
The process of exposing a material to nuclear radiation (the material does not become radioactive).
Why is it important to publish studies on the effects of radiation?
To allow findings to be independently checked (peer review).
