1.2 - The Development of the Atomic Model

What is a scientific theory?

an explanation agreed upon by a group of scientists who make predictions according to a theory

Who is John Dalton?

the man who came up with modern atomic theory and said that atoms are 'tiny solid spheres'

Who is J.J. Thomson?

he discovered the electron and the plum pudding model

What is the plum pudding model?

the idea that an atom was a ball of positive charge with negative electrons embedded

Who are Rutherford and Marsden?

did an experiment with alpha particles and found out that the nucleus has a positively charged nucleus

Explain Rutherford and Marsden's experiment?

They fired positively charged particles at a very thin sheet of golds, expecting most of them to go straight through, but some particles changed direction or deflected, leading to the theory that the nucleus is positively charged

Why did Rutherford and Marsden expect most of the particles to go through the atom?

Because they were using the plum pudding model and assumed that the positive charge was spread out

Who was Niels Bohr?

He proposed the idea that negative electrons were held in shells

Why did Niels Bohr think that electrons were held in shells?

if electrons were floating around the nucleus, the attraction would cause the atom to collapse

Who is James Chadwick?

He discovered the neutron

How did James Chadwick discover the neutron?

He realised that the mass of an atom is twice its expected value

Similarities between the plum pudding model and the modern nuclear model of the atom?

both have areas of positive charge, have electrons and both are neutral overall

Differences between the plum pudding model and the modern nuclear model of the atom?

plum pudding model has no nucleus, no neutrons or protons and no electron shells