P4 - Atomic Structure Flashcards
What are atoms
- Atoms are very small
* Have a radius of about 1x10(-10) metres
What is the basic structure of an atom?
Positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons
What is the radius of a nucleus
Less than 1/10000 of the radius of an atom
Where is most of the mass of an atom concentrated
In the nucleus
Electron arrangement (3)
- Electrons are arranged at different distances from the nucleus (different energy levels)
- Electron arrangements may change with the absorption of electromagnetic radiation
- Electron arrangement may also change by the emission of electromagnetic radiation
In an atom, what is the number of electrons equal to
The number of protons in the nucleus - so they have no overall electrical charge
What do all atoms of a particular element have
The same number of protons
Atomic number
(bottom) Is the number of protons in an atom of an element
Mass number
- Is the total number of protons and neutrons in an atom
* Is at the top
What do atoms of the same element have?
Different number of neutrons - these are called isotopes of that element
Isotopes
Occur when atoms of the same element have a different number of neutrons
What do atoms turn into when they lose one or more outer electrons
Positive ions
Differences between isotopes to differences in conventional representations of their identities, charges and masses (3)
- Some atomic nuclei are unstable
- The nucleus gives out radiation as it changes to become more stable
- This is a random process called radioactive decay.
Before the discovery of the electron what were atoms thought to be
Tiny spheres that could not be divided
Plum pudding model
Suggested that the atom is a ball of positive charge with negative electrons embedded in it
What was the conclusion made from the results of the alpha particle scattering experiment (2)
- That the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged
- This nuclear model replaced the plum pudding model
How did Niels Bohr adapt the nuclear model
By suggesting that electrons orbit the nucleus at specific distances
What did later experiments (after Niels Bohr) lead to the idea of (3)
- Led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles
- Each particle having the same amount of positive charge
- The name proton was given to these particles
Whose work provided evidence to show the existence of neutrons within the nucleus
James Chadwick’s
Why did the new evidence from the alpha particle scattering experiment lead to a change in the atomic model? (2)
- From the plum pudding model, they expected the particles to pass straight through the gold sheet or only be slightly deflected
- But although most of the particles did go straight through the sheet, some were deflected more than expected and a few were deflected back - which the plum pudding could not explain
Plum pudding model
Suggested that atoms were spheres of positive charge with tiny negative electrons struck in them like fruit in a plum pudding
Nuclear model (2)
- Realised that most of the mass of the atom must be concentrated at the centre in a tiny nucleus - this must also have a positive charge
- realised most of the atom is empty space
Atomic nuclei
- Are unstable
- The nucleus gives out radiation as it changes to become more stable
- This is a random process called radioactive decay
Activity
- Is the rate at which a source of unstable nuclei decays
* Measured in becquerel (Bq)
Count rate
Is the number of decays recorded each second by a detector (e.g Geiger-Muller tube)
4 ways nuclear radiation may be emitted
- Alpha particle (a)
- Beta particle (ß)
- Gamma ray (y)
- neutron (n)
Alpha particle (a)
Consists of two neutrons and two protons, it is the same as a helium nucleus
Beta particle (ß)
A high speed electron ejected from the nucleus as a neutron turns into a proton
Gamma ray (y)
• Electromagnetic radiation from the nucleus
Symbol for an alpha particle
Check photos
Symbol for a beta particle
Check photos
What is the half-life of a radioactive isotope? (2)
- Is the time it takes for the number of nuclei of the isotope in a sample to halve,
- Or the time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level
How to calculate the final activity as a percentage of the initial activity (2)
- Find the activity after each half-life
* Now divide the final activity by the initial activity, then multiply by 100 to make it a percentage
What is radioactive contamination?
Is the unwanted presence of materials containing radioactive atoms on other materials
What is the hazard from contamination due to?
The decay of the contaminating atoms- the type of radiation emitted affects the level of hazard
What is irradiation? (2)
- Is the process of exposing an object to nuclear radiation
* The irradiated object does not become radioactive
Hazards associated with irradiation and contamination (2)
- Cancers - as it can damage cells
* mainly cause harm
Why are findings of studies into the effects of radiation on humans important?
To be published and shared with other scientists so that the findings can be checked by peer review
