By Pablo By Pablo AcuñaAcuña..

IntroductionIntroduction

All materials are made of matter. All materials are made of matter. Matter is anything that has mass Matter is anything that has mass and volume. The basic buildings and volume. The basic buildings of matter are atoms.of matter are atoms.

For more than 2400 years, For more than 2400 years, philosophers and scientists have philosophers and scientists have tried to determine the tried to determine the composition of matter using a composition of matter using a variety of experiments and variety of experiments and observations. This is the history observations. This is the history of the atom…of the atom…

The History of the AtomThe History of the AtomThe History of the AtomThe History of the Atom

• Democritus ( more than 2000 years Democritus ( more than 2000 years ago): He is the first in think about ago): He is the first in think about the Atom.the Atom.

• John Dalton: In the early 1800, he John Dalton: In the early 1800, he proposed a theory. by his studies of proposed a theory. by his studies of the gases.the gases.

• J.J Thomson : In 1897, he J.J Thomson : In 1897, he discovered the electron studding discovered the electron studding the passage of an electric current the passage of an electric current through a gas. He created the through a gas. He created the model of the “pudding”model of the “pudding”

• Ernest Rutherford: In 1908, he Ernest Rutherford: In 1908, he discovered that the atoms discovered that the atoms have a nucleus and the have a nucleus and the electrons fly around, he use electrons fly around, he use the experiment of the golden the experiment of the golden sheet.sheet.

• Niels Bhor: In 1913 Bhor Niels Bhor: In 1913 Bhor proposed an improvement on proposed an improvement on the Rutherford model, that the the Rutherford model, that the electrons move in definite electrons move in definite orbits.orbits.

• The wave model: Bhor model The wave model: Bhor model worked well in explaining the worked well in explaining the structure of simple atoms, structure of simple atoms, today are based on the today are based on the principals of wave mechanics, principals of wave mechanics, this is that the atoms don’t this is that the atoms don’t move about the atom in move about the atom in definite path. definite path.

Democritus.Democritus.

The greek philosopher Democritus in more The greek philosopher Democritus in more than 2000 years ago, he and many others than 2000 years ago, he and many others philosopher ask this question: could matter philosopher ask this question: could matter be divided into smaller and smaller pieces be divided into smaller and smaller pieces for ever, or was there a limit to the number for ever, or was there a limit to the number of times a piece of matter could be divided?of times a piece of matter could be divided?

electron

neutron

proton

Democritus concluded that matter could not be divided into smaller and smaller particles for ever. Eventually the smallest possible piece would be obtained.

John DaltonJohn Dalton.

Dalton proposed that:Dalton proposed that:

In the In the earlyearly 1800 John Dalton 1800 John Dalton proposedproposed a a theory that said that:theory that said that:

• All elements are composed of atoms. All elements are composed of atoms. Atoms are indivisible and indestructible Atoms are indivisible and indestructible particles.particles.

• Atoms of the same element are exactly Atoms of the same element are exactly alike.alike.

• Atoms of diferent elements are differentAtoms of diferent elements are different• Compounds are formed by the joining of Compounds are formed by the joining of

atoms of two or more elements. atoms of two or more elements.

J.J. Thomson.J.J. Thomson.

Thomson proposed that the atom Thomson proposed that the atom is divided into smaller particles, is divided into smaller particles, he discovered the electron, he discovered the electron, studying the passage of an studying the passage of an electric current through a gas.electric current through a gas.

He proposed a model called “plum pudding" according to Thomson's atomic model, the atom was made of a puddinglike positively charged material throughout which negatively charged electrons were scattered, like plums in a pudding.

Ernest RutherfordErnest RutherfordHe discovered the He discovered the

separation among the separation among the nucleus an the nucleus an the electrons, he did and electrons, he did and experiment with a experiment with a positive ray that passed positive ray that passed right through a golden right through a golden sheet without changed sheet without changed is curse, with a is curse, with a exception of some that exception of some that change his curse, other change his curse, other that return, and another that return, and another that go vertical back.that go vertical back.

This probe that the This probe that the positives charges positives charges that go through the that go through the golden sheet didn’t golden sheet didn’t touch the nucleus, touch the nucleus, some passed nearly some passed nearly the nucleus and the nucleus and changed his curse, changed his curse, some touched some touched directly the nucleus directly the nucleus and returnand return.

electron

neutron

proton

Niels BohrNiels Bohr

He proposed an improvement in the He proposed an improvement in the Rutherford's model, the positions Rutherford's model, the positions of the electrons, in specifics energy of the electrons, in specifics energy levels, According to Bohr’s atomic levels, According to Bohr’s atomic model, electrons move in definite model, electrons move in definite orbits around the nucleus, much orbits around the nucleus, much like planets circle the sun, These like planets circle the sun, These orbits, or energy levels, are located orbits, or energy levels, are located at certain distances from the at certain distances from the nucleus.nucleus.

The wave modelThe wave model

According to the According to the modern atomic modern atomic model, an atom has model, an atom has a small positively a small positively charged nucleus charged nucleus surrounded by a surrounded by a large region in which large region in which there are enough there are enough electrons to make electrons to make the atom neutral.the atom neutral.

Know the exact location of the Know the exact location of the electron is impossible, the electron is impossible, the scientist only can predict where scientist only can predict where an electron is most likely to be an electron is most likely to be found.found.