Flashcards
2.1.1- The changing atom
Cards in this deck (8)
- 1What did Democritus believe?He suggested that you could divide a sample of matter only a certain number of times. Eventually you would be left with a particle that could not split any further. 'àtomos' , Greek for 'indivisible'.
- 2State Dalton's atomic theoryAtoms are tiny particles that make up elements that connot be divided.
All atoms of a given element are the same.
Atoms of one elemnt are different from those of every other elemnt.
Used his own symbols and developed first table of atomic masses. - 3J.J. Thompson discovers electronsCathode rays( electrons) were a stream of particles that had a negative charge.
Could be deflected by both a magnet and an electric field.
They had a very very small mass.
Electrons moving in a 'sea' of positive charge. Known as the plum-pudding atom. - 4Ernest Rutherford's gold-leaf experimentDirected alpha-particles towards a sheet of very thin gold foil.
Most particles were not deflected at all.
Small percentage deflected at large angles.
very few deflected back towards the source. - 5Conclusions made from Rutherford's experimentThe positive charge of an atom and most of its mass are concentrated in nuclear, at the centre.
Negative electrons orbit the nuclear.
Most of an atom's volume would be the space between the nuclear and orbiting electrons.
The overall positive and negative charges must balance.
- 6Niels Bohr's planetary model Henry Moseley's work on atomic numbersBohr altered Rutherford's model to allow electrons to only follow certain paths(shells). Helped to explain spectral lines seen in emission spectra and the energy of electrons at different distances from the nucleus. Moseley discovered a link between X-ray and frequencies (i.e. its order in the period table but couldn't explain this.
- 7Rutherford discovers the proton Wave and particle behaviourThe discovery of the proton was able to explain Moseley's finding that an atom's atomic number was linked to X-ray frequencies. We now know that an atom's Atomic number tells us the number of protons in an element.
Louis de Broglie suggested that particles could have the nature of both a wave and a particle.
Erwin Schrödinger suggested that an electron had wave-like properties. Also introduced the idea of atomic orbitals. - 8James Chadwick discovers the neutron Modern DayObserved a new type of radiation emitted from some elements. He showed that this radiation was made up of uncharged particles with a similar mass to that of a proton.
It is now thought that protons and neutrons are made up of even smaller particles called quarks.
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- A level Chemistry (2.1- Atoms and Reactions) Flashcards on 2.1.1- The changing atom, created by Ben Geeman on 06/02/2017.
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