History of the Atom and Isotopes Flashcards
What is an isotope?
Atoms with the same number of protons but different numbers of neutrons
Why do isotopes have the same chemical properties?
They have the same configuration of elements
What physical properties do isotopes have and why?
Different densities and rates of diffusion - because physical properties tend to depend more on the mass of the atom
What was John Dalton’s Theory about the atom? (Part 1)
Proposed that all matter was composed of atoms - indivisible and indestructible building blocks.
What is John Dalton’s theory about atoms? (part 2)
At the start of the19th century y John Falton described atoms as solid spheres and said that spheres made up different elements
What was JJ thompson theory on atoms? Part 1
Concluded from his experiments that an atom must contain even smaller negatively charged particles - electrons.
What was Jj Thomspon’s theory on the atoms? (Part 2)
Discovered The new model known as the “plum pudding model”
What was Rutherford theory on atoms?
In 1909, he conducted the gold foil experiment - fired positively charged alpha particles at a very thin sheet of gold foil
What was the results of the gold foil experiment?
most alpha particles passed straight through the gold atoms and a very small number were deflected backwards.
What model did Rutherford come up with?
The nuclear model
What is in the nuclear model?
There’s a tiny positively charged nucleus at the centre surrounded by a “cloud” of negative electrons
What did Rutherford describe most of the atoms as?
“Empty space”
What was wrong with the nuclear model?
Scientists realised that electrons in a “cloud” around the nucleus of an atom would quickly spiral down into the nucleus causing the atom to collapse
What principles did Neil’s Bohr propose? (1 and 2)
- electrons only exist in fixed orbits (shells)
- each shell has a fixed energy
What principles did Neil’s Bohr propose? (3 and 4)
- when an electron moves between shells electromagnetic radiation is emitted or absorbed
- because the energy of the shells is fixed, the radiation will have a fixed frequency
