History of the Atom Flashcards
(10 cards)
At the start of 19th century what did John Dalton suggest
Atoms are solid spheres, different spheres made up the different elements
in 1897 what did JJ Thompson conclude ?
Atoms are not solid spheres
His measurements of charge and mass showed atoms must contain smaller - charged particles = electrons
How is JJ Thompsons theory shown ?
Plum pudding model
an atom was a sphere of positive charge, with negatively-charged
electrons
embedded in it.
What occurred in 1909 ?
What is the alpha scattering experiment ?
Ernest Rutherford and his student Ernst Marsden conducted the famous alpha scattering experiment.
They fired positively charged particles at a thin sheet of gold. They expected the particles to pass through the sheet because it was believed that the positive charge of each atom was thought to be spread out through the ‘pudding’ of the atom.
How did Rutherford explain this new evidence
nuclear model of the atom
Tiny + charged nucleus at the centre where most of mass is most concentrated .
Cloud of negatively charged electrons surround this nucleus - most of atom is empty space . When alpha particles came near the concentrated + charge of the nucleus, they were deflected. Fired directly at nucleus = deflect back .
Other wise pass through empty space
Why was Rutherford’s evidence incorrect to an extent ?
electron in the cloud of the nucleus would be attracted to the nucleus causing the atom to collapse
Niels Bohr’s nuclear model of the atom
electrons contained in shells
electrons orbit the nucleus in fixed shells
Each shell in fixed distance from nucleus
Why was Niels Bohr’s nuclear model of the atom supported ?
supported by other experiments and helped to explain a lot of other scientists observation at the time
Further experiments
1) Rutherford and other showed that the nucleus can be divided into smaller particles which had same charge as hydrogen nucleus = proton
2) James Chadwick carried out an experiment which provided evidence for neutral particles in nucleus = neutrons
modern day model of atom
nuclear model
