Ch 30: The Atom, the nucleus and radioactivity Flashcards
Ernest Rutherford, 1911
Bombarded gold with helium nuclei (alpha-particles) to find the structure of the atom
Rutherford’s experiments conclusions
- nucleus as all positive charge and is v small compared to full atom
- electrons orbit nucleus
Niels Bohr, 1913
Proposed an atom model based on emission spectra
Emission spectra
the pattern formed when light from a luminous source undergoes dispersion, i.e. if sufficient energy is provided to a solid, liquid or gas the atoms may give out light and a spectrum is formed when this light is put through a grating
Continuous spectrum
emission spectrum produced by a solid/liquid. All wavelengths are emitted and spectra do not differ with different materials
Line spectrum
emission spectrum produced by gaseous element. Colour of light depends on gas. Each element has a different line spectrum.
Energy level
fixed energy value that an electron can have in an atom
Electromagnetic radiation is given out by an electron when…
An atom is given sufficient energy for an electron to jump an energy level, stays there for a short time then drops back down
Amount of e.m. radiation given out by an electron when jumping down an energy level is…
The higher energy level - the lower energy level
L.A.S.E.R =
Light Amplification by a Stimulated Emission of Radiation
What is a LASER
When the exact moment an electron returns to a lower energy level and lets out e.m. radiation is coordinated so that intense light is given out.
Uses of LASERs
- telecommunications
- medicine
- industry
Isotopes
atoms of an element that have the same no. of protons but different no. of neutrons
Alpha radiation
Fast moving helium nuclei ejected from the nuclei of radioactive atoms. 2 protons, 2 neutrons
Beta radiation
High speed electrons emitted form the nuclei of radioactive atoms
Gamma radiation
High frequency electromagnetic radiation emitted from the nucleus of a radioactive atom.
Becquerel, 1986
found uranium gave out radiation
Radioactivity
The disintegration of the nuclei of certain atoms with the emission of one or more types of radiation
Why does radiation occur?
The nuclei of certain isotopes are unstable, they contain excess energy and they get rid of this through radioactive decay.
Activity of a radioactive substance
The number of nuclei of that substance decaying per second, unit = becquerel
1 becquerel =
1 radioactive decay per second
The laws of radioactive decay
We cannot predict:
- Which nuclei will decay next
- When a given nucleus will decay
i. e. radioactivity is a random process
No. of nuclei decaying per second is dir. pro. to…
the number of nuclei undecayed
Half life(T1/2)
the time taken for half of the undecayed atoms to undergo decay, T1/2 =ln2/wavelength
