Models of Atomic Structure

Question 1

In the past, different models of atomic structure were accepted, why?

Answer 1

In the past, different models of atomic structure were accepted because they fit the evidence available at the time. As scientists did more experiments, new evidence was found and the models were modified to fit it

Question 2

What was the first model of atomic structure?

Answer 2

At the start of the 19th century John Dalton described atoms as solid spheres, and said that different spheres made up different elements

Question 3

What was the second model of atomic structure?

Answer 3

In 1897 J.J.Thompson discovered the electron. This showed atoms weren’t solid. The new model of atomic structure was known as the ‘plum pudding model’

Question 4

What was the third model of atomic structure?

Answer 4

In 1909, Ernest Rutherford and his students Hans Geiger and Ernest Marsden conducted the gold foil experiment. They fired positively charged alpha particles at a very thin sheet of gold. The plum pudding model suggested that both of the alpha particles would be deflected back by the ‘pudding’ that made up most of the atom. Most of the particles passed through with only a small number being deflected. The plum pudding model couldn’t be right, so Rutherford developed the nuclear model of the atom. In this, a tiny positively charged nucleus is surrounded by a ‘cloud’ of negative electrons

Question 5

What was the fourth model of atomic structure?

Answer 5

Scientists realized that electrons in a ‘cloud’ around the nucleus would spiral down into the nucleus, causing the atom to collapse> Niels Bohr proposed that electrons exist in shells or orbits of fixed energies. When electrons move between shells, electromagnetic radiation is emitted or absorbed. The Bohr model fitted experimental observations of the radiation emitted or absorbed by atoms

Question 6

Why wasn’t the Bohr model quite right?

Answer 6

Scientists discovered that not all electrons in a shell have the same energy. They refined the Bohr model to include sub-shells. The Bohr model isn’t perfect and more accurate models exist today, but it’s simple and explains many experimental observations