the history of the atom Flashcards
who developed the plum pudding theory and when?
JJ Thomson, 1897
what did John Dalton describe atoms as and when?
small solid spheres, start of 18th century
what was the plum pudding model?
a model which showed the atom as a ball of positive charge with electrons embedded in it
what experiment did ernest rutherford conduct and when?
alpha scattering, 1909
what was the alpha scattering experiment?
they fired positively charged alpha particles at an extremely thin sheet of gold
what were the results of the alpha experiment expected to be?
expecting particles to pass straight through the sheet or be slightly deflected at most
why were the results predicted as they were?
the positive charge was thought to be spread out through the atom
what were the actual results of the alpha experiment?
most of the particles went straight through, some were deflected more than expected and some were deflected backwards
why did some particles pass straight through?
they passed through the empty space
why did some particles deflect?
they passed close to the nucleus
why did some particles deflect backwards?
they were fired at the nucleus
what was rutherford’s model called?
the nuclear model
what was the nuclear model?
there’s a positively charged nucleus at the centre where most of the mass is concentrated, a cloud of negative electrons surrounds the nucleus so most of the atom is empty space
who suggested electrons were in shells and when?
neils bohr, 1913
why was rutherford’s model proved wrong?
scientists realised electrons around the nucleus would be attracted to it, causing the atom to collapse
what did bohr propse?
electrons orbit the nucleus in fixed shells
how long after the acceptance of nuclei were protons discovered?
20 years
who carried out an experiment which provided evidence for protons and when?
james chadwick, 1932
what did james chadwick provide evidence for?
the existence of neutrons in the nucleus
why are dalton’s ideas still useful today?
scientists use the particle model which is similar
what were the findings of rutherford’s experiment?
the mass of the atom is concentrated at the centre
difference between rutherford and bohr’s model?
rutherford’s has electrons in rings that crossover around the nucleus but bohr’s has electrons in fixed shells
