History And Development Of Atoms and The Peridic Table Flashcards
The history of the periodic table before/at the plum pudding method
Start of 19th century: John Dalton described atoms as solid spheres and said different spheres were made up of different elements
1897: JJ Thompson concluded from experiments that atoms weren’t solid spheres
He thought an atom must contain something smaller, and negatively charged - electrons
JJ THOMPSON made the plum pudding method
In the plum pudding, it was a ball of positive charge with electrons stuck in it
Who proved the plum pudding method was wrong/who made the Nuclear model of the atom
Ernest Rutherford and Ernest Marsden, 1909
How was the plum pudding method proved to be wrong
Rutherford and Marsden conducted the ALPHA PARTICLE SCATTERING EXPERIMENT by firing alpha particles at a thin sheet of gold
From the plum pudding, they expected the A.particles to pass straight through as the positive charge of the atom was thought to be throughout the pudding
some went straight through, but some were deflected and some were rebounded
What did the nuclear model of the atom consist of?
There was a positively charged nucleus where most of the mass was, and a “cloud” of electrons surrounded it, so most of the space was empty.
How was Rutherford’s nuclear model proved to be right
The alpha particles past through the “cloud of electrons” straight, but were rebounded/deflected at the nucleus
How was Bohrs nuclear model proved even more right than Rutherford’s
As the “cloud” of electrons would cause the atom to collapse
So he proposed fixed shells at a fixed distance
Who proved the existence of protons
Rutherford and others showed the nucleus could be divided into even smaller particles
What did James Chadwick prove
Evidence for neutral particles in the nucleus - neutrons
What was wrong with early periodic tables
They were categorised by either their physical and chemical properties, or their relative atomic mass
No such thing as atomic number
They were not complete and some elements were placed in wrong places
Who made the periodic table we know today
Dmitri Mendeleev, 1869
What was so good about the new periodic table that guy made
He left gaps for new atoms to be discovered.
These gaps were later filled and put in olace
He also mostly put them in order of their atomic mass
