history of the atom Flashcards
who were the first to have ideas about particles and atoms ?
Ancient Greeks
what did John Dalton suggest about atoms ?
He suggested that substances were made up of atoms that were like tiny, hard spheres. he also suggested that each chemical element had its own atoms that differed from others in their mass. Dalton believed these atoms could not be divided or split.
what did John Dalton suggest about atoms in chemical reactions ?
he suggested that atoms re-arranged themselves and combined with other atoms in new ways.
how are Dalton’s ideas still useful today ?
they help to visualise elements, compounds and molecules.
his modes are still used to describe the different arrangement and movement of particles in solids, liquids and gases.
what did J.J. Thomson discover ?
he discovered the electron. This is a tiny, negatively charged particle that was found to have a mass about 2000 times smaller than the lightest atom.
How did Thomson do his experiments ?
applied high voltages to gases at low pressure
what did geiger and Marsden find out 10 years later ?
they were doing an experiment with radioactive elements.
they were firing dense, positively charged particles at the thinnest piece of gold foil they could make.
they expected the particles to pass straight through gold atoms its their diffuse cloud of positive charge.
their results suggested a new model for the atom.
what did rutherford suggest?
the positive charge must be concentrated at a tiny spot in the centre of the atom. otherwise large positive particles fired at foil could never be repelled back towards their source. The electrons must be orbiting around the nucleus, contained dense positively charged protons.
what did Niels Bohr notice in 1914 ?
light is given out when atoms are heated - specific amounts of energy.
suggested the electrons must be orbiting nucleus at set distances, in certain energy levels (shells).
energy given out when electrons fall from his to low energy levels. Bohr match his model to energy values observed.
what did scientist speculate about the nucleus ?
there were two sub-atomic particles inside of it. They had evidence of protons but second sub-atomic particle in nucleus-explained the missing mass being noticed in atoms.
what did James Chadwick do in 1932 ?
did an experiment that could only be explained by the existence of neutrons-confirmation.
