Proof of Atomic Structure

Atom is the smallest unit for an element to maintain its chemical characteristic. It is so tiny

that it can not be directly observed with the present technology, which means that we are not sure

about its structure now. However, scientists did experiments and tried to work something out.

English scientist J.J. Thomson improved on the work of Wilhelm Wien and Eugen

Goldstein and created a mass spectrograph. A mass spectrometer can only detect one isotope at a

time. By varying the strength of the magnetic field, ions of other mass can be detected. Therefore,

mass spectrometer proves that an element can have atoms of different masses, which are called

isotopes.

When we give atoms energy, like passing an electrical discharge through the gas of an

element at low pressure, the element will be excited can emit light of a characteristic colour. This

is called atomic emission spectra. It is the most effective way to prove the electronic structure of

atom. It proves that electrons of an atom is surrounding the nucleus in certain allowed energy

levels or orbits.

Another proof of the atomic structure is the ionization energy. Ionization energy is the

energy required to remove one mole of electrons from one mole of atoms in the gas phase.

Ionization energy varies with group, period. Ionization energy decreases group by group because

of more shielding and distance. It increases period by period because of more protons thus more

attraction. Little decreases can be explained with the sublevels and orbital. Therefore, ionization

energy proves the theories of energy level, sublevels, orbital, and the electron capacity.

There are other features to prove the atomic structure, like melting point and

electronegativity. Melting point proves the difference of structure of different phase and category

of elements. For example, metal has higher melting point because the electrons of atoms are

highly attracted to each others, except mercury, as mercury has a different atomic structure.

Although we can not see atom directly, we know quite a lot about them, because human are

intellegent.

http://en.wikipedia.org/wiki/Mass_spectrometry

Chemistry textbook by John Green and Sadru Damji

“It is the coldest temperature theoretically possible and cannot be reached by artificial or natural

means, because it is impossible to decouple a system fully from the rest of the universe.”

http://en.wikipedia.org/wiki/Absolute_zero