The Atom

Everything with see is made of atoms

Everything with touch

Everything with taste

Everything with smell

What is an Atom? Democritus described it as the

smallest piece of matter that could not be divided into smaller pieces the world atom means not to be cut.

Then John Dalton proposed the atomic theory of matter based on his experimental observation.

He said that: All matter is made of atoms. Atoms are

indivisible and indestructible. All atoms of a given element are identical

in mass and properties. Compounds are formed by a combination

of two or more different kinds of atoms. A chemical reaction is a rearrangement of

atoms. Atoms can be neither created nor

destroyed

Then in 1807 Thomson proposed the plum pudding model or chocolate chip cookie model.

An atom is a sphere of which is positive and an electron that has a negative charge embedded in it.

The positive and negative charge in the atom are equal in magnitude. That’s why atoms are electrically neutral.

In 1869 Dmitri Mendeleev classified the elements by the atomic weight. He arranged the elements of increasing. He discovered that there existed a periodicity of elemental properties

Then in 1911 Rutherford describe the atom with the nucleus and the vast majority of the atom as empty space.

Then Neil's Bohr refined Rutherford's proposing that electron

orbits the nucleus without losing energy Can move only in fixed orbits of specific

energies. Electrons with low energy would orbit

closer to the nucleus while electrons with high energy orbit further from the nucleus.

Then in 1932 James Chadwick discover the neutron . He said that the neutron has significant mass and no charge

The modern quantum cloud model

carbon

Conclusion:

Atoms are composed of three elementary particles: the electron, the proton and the neutron.

Conclusion:

Most of the mass of the atom is concentrated in the nucleus of the atom. The protons and the neutrons are at the center. And electrons are outside the nucleolus.

In neutral atoms, the number of protons is equal to the number of electrons.

Conclusion:

The type of element each atom is determined by the number of protons it has.

Conclusion:

carbon

helium

The number of protons in an element is equal to the atomic number - the number on which the periodic table is based.

Conclusion:

Isotopes are atoms of the same element with different masses.

Conclusion:

The mass number is the sum of the number of protons and neutrons in a particular atom. The mass number is different for different isotopes of the same element.

Conclusion:

References:

http://web.neo.edu/rjones/Pages/1014new/Lecture/chemistry/chapter_8/pages/history_of_atom.html

http://profmokeur.ca/chemistry/history_of_the_atom.htm