History of the atom and the periodic table

The atom:

Early 1800s:

• John Dalton described atoms as solid spheres; different spheres made up element

1897:

• J J Thomson concluded atoms werent solid spheres. his measurements of charge and mass showed that the atom must contain even smaller, negatively charged particles - electrons
• the new therory was called the "plum pudding model" - a ball of positive charge with electrons stuck in it

1909:

• Earnest Rutherford conducted the famous alpha particle scattering experiments.
• they fired positivey charged alpha particles at an extremely thin sheet of gold
• from the plum pudding model, they were expecting the particles to pass straight through the sheet of be slightly deflected. this was because the positeve charge of each atom was thought to be spread out through the pudding of the atom. but some were deflected backwards so the plum pudding model couldnt be correct
• Rutherford made a new model - the nuclear model
• when the alpha particles came near the concentrated, the positive charge fo the nucleus they were deflected. if they were fired directly at the nucleus they were defleced backwards. otherwise they passed through the empty space

Bohr:

• scientists realized that if the electrons were in a cloud around the nucleus of the atom as Rutherford described, they would be attracted to the nucleus, causing the atom…