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Chemistry - Atomic Structure

Atoms are the tiny particles of which everything is composed of. For some time the atom was thought to be the smallest part of matter that could exist.

Scientists soon discovered that atoms are composed of even smaller particles known as subatomic particles.

Scientists also discovered that no matter what the element, the same subatomic particles make up the atom.

The only variable is the number of the subatomic particles.

In order to be successful in chemistry you only need to be concerned with the three major subatomic particles, which are:

Protons, Neutrons and Electrons.










Mass (g)


Mass (amu)











1.673 X 10 -24









n °




1.675 X 10 -24









e ­




9.109 X 10 -28




Outside nucleus

In the above table the masses of the subatomic particles are listed in two ways; grams and amu (atomic mass units), expressing mass in amu is far easier than using the gram equivalent.

As you can see in the last column of the table that the protons and neutrons are found in the nucleus of atoms, whereas the electrons are found around the nucleus at different energy levels called electron shells.

Each electron shell can hold up to a certain number of electrons, when each shell surrounding the nucleus is filled, a new shell is formed and starts to fill.

The subatomic particles are held together by electrical charges, as you can see from the table.

Particles with opposite charges are attracted to one another, so particles with like charges repel one another.

An atom usually has an equal number of positively charged protons and negatively charged electrons, making the atom itself electrically neutral.

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