This theory explains that the matter consists of indivisible atoms, each of which is unique to its element.

It is characterized by the following reasons:

-Atoms are solid, indivisible particles.

-Atoms of the same element are identical in mass and properties.

-Atoms cannot be created or destroyed, they only separate or combine with each other in different groups, to form different compounds.

-Compounds are formed by a combination of different atoms in a fixed number.

It is characterized by the following reasons:

- The atom is a uniform sphere of positively charged matter.

• Almost all the mass of the atom is spread throughout the sphere, so the atom has a very low density.

• It is a sphere of positive charge with almost all the mass of the atom.

- Electrons are embedded in the sphere.

- The atom is electrically neutral: no. (+) charges = no. (-) charges

Can be divide in two parts:

The nucleus

• It is located in the centre of the atom.

• It is very dense, because it contains almost all of the mass of the atom in a very small volume.

• It has all the positive charge.

The extra nuclear part

• It is most of the space of the atom.

• It is largely empty.

• The negatively-charged electrons revolve around the nucleus in closed orbits attracted by its positive charge.

This theory explains that the electrons orbit the nucleus in fixed energy levels or shells.

It is characterised by:

• Electrons move in specific, quantized orbits with fixed energy levels.

• Electrons can jump between energy levels by absorbing or emitting energy.

• This model explained the line spectra of elements like hydrogen.

• Bohr introduced the concept of quantized angular momentum for electrons.