C1.2.3 Developing The Atomic Model Flashcards
What did dalton do and when?
-In 1803, John Dalton suggested that all matter is made from atoms.
-Others had already suggested but his model was more detailed.
It also explained evidence from his experiments on gases:
All atoms of an element are identical
Different elements contain different types of atom
What did dalton think atoms were
He didn’t know they existed, believed they were tiny solid balls. Technology at the time didn’t let him investigate atoms in further detail
What did Thompson do? When?
-Discovered the first subatomic particle, the electron, in 1897.
-He found that beams of ‘cathode rays’ changed direction in electric and magnetic fields.
-Concluded that those rays were actually tiny particles that were negatively charged and way smaller than atoms.
His model made sense of two observations:
Atoms contain electrons
Atoms are neutral overall
What did his plum pudding model suggest?
That atoms are spheres of positive charge with electrons dotted around inside
What did Rutherford do? When? With who?
-In 1909, he tested the plum pudding model with Hans Geiger and Ernest Marsden.
-They pointed beams of positively charged particles called alpha particles, at thin gold foil.
-Most went straight through the foil
- Some changed direction or came straight back as if they’d been pushed away.
-Concluded that an atom has a positively charged nucleus containing most of the atoms mass.
-Surrounded by electrons/ mostly empty space in atom
What did Bohr do? When?
Realised that orbiting electrons would be attracted to the oppositely charged nucleus and would rapidly spiral inwards. In 1913 he used mathematical models to improve Rutherford’s model. Bohr showed that electrons occupy fixed energy levels, or shells, around the nucleus
