Atomic Models Flashcards
What did ancient Greeks think all matter was made of?
Indivisible particles.
What did John Dalton describe atoms as?
Solid spheres - he said different spheres made up different elements.
Who said atoms were solid spheres and when did he say this?
John Dalton, start of 19th century.
Who discredited John Dalton’s theory and when?
JJ Thompson in 1897.
How did JJ Thompson discredit Dalton’s theory?
Measured charge and mass of an atom which showed that atoms must contain even smaller, negatively charged particles - ‘electrons’. He concluded that atoms weren’t solid (Dalton) or indivisible (ancient Greeks).
What model came about due to Thompson’s findings?
The Plum Pudding Model - a positively charged sphere with negative electrons embedded in it.
Who showed that the Plum Pudding Model was wrong?
Rutherford with students Geiger and Marsden.
What experiment did Rutherford and his students carry out to discredit the Plum Pudding Model?
They fired positively charged alpha particles at a thin sheet of gold. They expected most particles to be deflected due to the positive charge of the ‘pudding’ that made up most of the atom. However most particles passed straight through and a very small amount were deflected. This showed the plum pudding model was wrong. Rutherford came up with the nuclear model to replace it.
What did Henry Moseley discover?
He discovered that the charge of the nucleus increased from one element to another in units of one.
What did Henry Moseley’s discovery lead to Rutherford doing?
Further investigate the nucleus. He finally discovered protons which explained the charges of different nuclei.
What final problem did the model of the atom face after protons were discovered?
The nuclei of atoms were too heavy to just contain protons - Rutherford predicted there to be one other type of particle in the nucleus which had a mass but no charge.
Who discovered the neutron?
James Chadwick.
What were the four principles of the Bohr Model?
1) Electrons can only exist in fixed orbitals (if electrons existed in a cloud around the nucleus they would spiral down into the nucleus and the atom would collapse). 2) Each shell has a fixed energy. 3) When an electron moves between shells, electromagnetic energy is emitted or absorbed. 4) Because the energy of shells is fixed, the radiation will have a fixed frequency.
What does Bohr’s model explain about the noble gases?
It explains why they are inert - the shells of an atom can only hold a fixed number of electrons and its reactivity is due to its electrons. Therefore, when an atom has full electron shells, it is stable and doesn’t react.
What is the most accurate model of an atom we have today?
The quantum model.
