History of atoms and the atomic table Flashcards
What did John Dalton believe about atoms
He described them as solid spheres, and that different spheres were made up of different atoms
What did J J Thompson discover about what John Dalton thought about atoms in 1897
he concluded that the spheres werent solid
he measures mass and charge and decided that the atoms must contain even smaller negatively charged particles called - electrons
What was J J Thompson’s new theory?
The plum pudding model
had an atom as a ball of positive charge and had electrons stuck in it
Who proved Thompson’s theory wrong and when?
Ernest Rutherford did in 1909
How did Rutherford conduct an experiment to prove the plum pudding model wrong?
They fired positively charged alpha particles at a very thin sheet of gold
They though that based on the plum pudding model they were expecting the particles to pass straight through the sheet or have slight deflections. as the positive charge was believed to be spread out across the atom
But instead they got the expected result however some were deflecting more than expected or reflected back completely
So this disprooved the plum pudding model theory
What was Rutherford’s theory?
The nuclear model of the atom
Thought that there was a very small positive nucleus at the centre of the atom where most of the mass was concentrated, then a ‘cloud’ of negative electrons surround the nucleus. So most of the atom is empty space
What was Bohr’s theory
He suggested that all the electrons were organised into fixed energy shells that orbit the nucleus instead of just a ‘cloud’, as if they were the atom would collapse as the positively charged nucleus would attract the negative electrons.
What else did Ernest Rutherford discover apart from the fact that atoms aren’t solid?
He discovered protons by further conducting experiments on the nucleus.
What did James Chadwick discover?
That there were also neutrally charged particles in the nucleus and he called them neutrons.
What is the current atom model that we believe to be true today called?
The nuclear model
How was the periodic table organised in the early 1800s?
The known elements were arranged by atomic mass
Why couldn’t they organise it in any other way bck in the 1800s
This was because they had no common knowledge of atomic numbers or the advances in atomic structure back then
Why were the periodic tables wrong back in the 1800s?
As the elements were placed in order of relative atomic mass and did not take into account for their properties
Who discovered the modern periodic table? and when?
Dmitri Mandeleev in 1869
How did Mandeleev organise the periodic table?
He mainly put them in order of atomic mass, but switched the order if the properties of the element meant that is should be moved to another series of similar elements.
