The History of the Atom Flashcards
What did John Dalton say at the start of the 19th century?
He said that atoms were like solid spheres and said that different spheres made up of different elements.
Which man proved John Dalton wrong in 1897?
J J Thomson.
What did J J Thomson conclude from his experiments.
He concluded that atoms weren’t solid spheres. His measurements of charge and mass showed that an atom must contain smaller, negatively charged particles that we know as electrons. This theory is was known as the plum pudding model.
What was the plum pudding model?
It showed that the atom was a ball of positive charge (the pudding) with electrons stuck in it (the plums).
Which two men showed that the plum pudding model was wrong in 1909?
Ernest Rutherford and his student Ernest Marsden.`
How did Rutherford and his student prove J J Thomson wrong?
They fired positively charged particles at an extremely thin sheet of gold. They were expecting the particles to pass through the sheet or be slightly deflected at most (from the plum pudding model). Some of the particles went straight through and some were deflected (more than expected). A small number were deflected backwards - this proved the plum pudding couldn’t be right
What was thought about the positive charge of each atom from the plum pudding?
That the positive charge of each atom was to be very spread out through the ‘pudding’ of the atom.
What did Rutherford do the explain his new evidence?
He created the nuclear model of the atom. In it there was a tiny, positively charged nucleus at the centre where most of the mass in concentrated. A cloud of negative electrons surround the nucleus so most of the atom is empty space.
What happens if an alpha particle goes near a nucleus or is fired directly at it?
Alpha particles coming near the concentrated, positive charge of the nucleus were deflected. If it was fired directly at the nucleus it would be deflected backwards, otherwise they passed through the empty space.
What did scientists discover about Rutherford’s nuclear model?
The electrons is an cloud around the nucleus of an atom would be attracted to the nucleus causing the atom to collapse.
What did Niels Bohr suggest about electrons with his own nuclear model.
It suggested that all the electrons were contained in shells and that electrons orbit the nucleus in fixed shells and aren’t anywhere in between. Each shell is a fixed distance from the nucleus.
What did Rutherford’s further experiments show?
They showed that the nucleus can be divided into smaller particles which each have the same charge as a hydrogen nucleus. These particles were called protons.
What did James Chadwick discover about the nucleus?
He discovered that there are neutral particles in the nucleus which are now called neutrons.
