Atomic Models - Class 9 PDF Download

    Thomson's model of an atom

• It was the very first and most basic model of an atom that was taken into consideration.
• The model of the atom was proposed to be similar to that of a watermelon.
• The positive charge in the atom was considered as the red edible part of the watermelon.
• The negatively charged electrons were considered as the black seeds embedded in the red part.

Rutherford Model

• Rutherford carried out an alpha- particle scattering experiment in which a large fraction of alpha particles bombarded towards the gold sheet passed through it without any deflection. Some got deflected by very small angles. Very few were deflected back as it is.
• The particles which passed as it is concluded that most of the space in an atom is empty. The particles which were deflected by small angles concluded that positive charge in an atom is not uniformly distributed. Very few deflected back particles concluded that the volume occupied by positively charged atoms is very small.

• The conclusion of the experiment was- In the center of atom, the positive charge resides which is called nucleus. Almost all the mass of atom resides in nucleus. The size of the positively charged nucleus is very small as compared to the size of the atom. Electrons revolve around the nucleus in well-defined orbits.

Question- What is the main difference between Rutherford's model of atom and Thomson's model of atom?

Answer- Rutherford suggested that most of the atom is empty and the negative charge just revolve around orbits while positive charge remains intact in center of the atom. Thomson suggested that both negative and positive charges occupy the full atom and there is not any free space inside an atom. Positive charge is the red part of watermelon while negative charge are the seeds of water melon.