1How did John Dalton describe atoms in the early 19th century?
As solid spheres, with different spheres making up different elements
2Who discovered the electron, and what did this discovery change about atomic theory?
J.J. Thomson discovered the electron, showing atoms were not solid and indivisible, leading to the "plum pudding model."
3What was the "plum pudding model" of the atom?
A model where atoms were seen as a positive ‘pudding’ with negatively charged electrons scattered within it.
4What experiment did Rutherford and his students conduct in 1909?
They conducted the gold foil experiment, firing positively charged alpha particles at a thin sheet of gold.
5What result from the gold foil experiment disproved the "plum pudding model"?
Most alpha particles passed straight through the gold, with only a few deflecting backward, indicating that the atom is mostly empty space.
6What atomic model did Rutherford propose after the gold foil experiment?
The nuclear model, where a tiny positively charged nucleus is surrounded by a 'cloud' of negative electrons.
7Why did Rutherford’s nuclear model suggest the atom would collapse?
Electrons in a 'cloud' would spiral into the nucleus, causing instability.
8What did Niels Bohr propose to solve the issue with Rutherford’s model?
He proposed that electrons exist in fixed shells or orbits of energy levels.
9What happens when electrons move between shells in Bohr's model?
Electromagnetic radiation of fixed energy or frequency is emitted or absorbed.
10Why was Bohr's model refined after further discoveries?
Scientists found that electrons within the same shell could have different energies, leading to the concept of sub-shells.
11Why is the refined Bohr model still useful today?
It is simple and explains many experimental observations, like bonding and ionization energy trends.