The Process of Its Discovery by Famous Dead Guys The Atom The Process of Its Discovery by Famous Dead Guys

Ancient Greek Ideas Matter is composed of atoms Atoms are solid, homogeneous, indestructible, and indivisible Different kinds of atoms have different shapes & size Size, shape, and movement of atoms determine the properties of matter REJECTED IDEAS BY MANY BECAUSE POOR DEMOCRITUS WAS NOT A POPULAR GUY…

And Mr. Popularity goes to… Aristotle! He had a HUGE influence on society at the time. He said that empty space cannot exist. Matter is made of earth, fire, air, and water. For 2,000 years, people agreed with Aristotle, which we know is nonsense today.

Dalton revived Democritus’ ideas and added more! Matter is composed of atoms Atoms are indivisible & indestructible Atoms of a given element are identical in size, mass, and chemical properties Atoms of one element are different than those of atoms of a different element Different atoms combine in simple whole-number ratios to form compounds Atoms are separated, combined, or rearranged in a reaction

Dalton was not correct on all accounts Atoms are divisible into smaller particles yet – subatomic particles. Not all atoms of a specific element were the same – some carried slightly different mass. J.J. Thomson discovered the electron, the first subatomic particle. He was not well received for a while, but later won a Nobel Prize.

Furthermore, Thomson created “Plum Pudding Model” If electrons carry a negative charge, then why is matter neutral? If an electron is so small, what makes up the rest of the atom? Matter containing uniformly distributed positive charges in a sphere shape resided with those negatively charged particles called electrons.

Rutherford = Radioactive Particles Sent alpha particles through gold foil Rutherford thought the particles would be slightly deflected from all of that “plum pudding” Whoa! Some alpha particles went through the foil while some bounced back to the origin and some deflected at various angles. Rutherford developed the idea of a NUCLEUS, where positive charges reside.

Then Bohr came along… Knew that electrons behaved kind of like a wave. Working for good ol’ Rutherford, Bohr came up with a QUANTUM MODEL. Electrons can change energy levels The larger the electron’s orbit, the higher the atom’s energy level.

J. Chadwick moving ahead Worked for Rutherford & Bohr Discovered another subatomic particle besides the electron and proton – the NEUTRON Mass is similar to proton, but carries no charge Another Nobel Prize winner!

Bohr’s ideas were good, but… It was discovered that electrons do not move about the nucleus in circular orbits. However, his ideas did lay the groundwork for the QUANTUM MECHANICS MODEL.

De Broglie had questions If waves can have particle-like behavior, could particles of matter (including electrons) behave like waves? He knew that if an electron has wavelike motion and is restricted to circular orbits of fixed radius, only certain wavelengths, frequencies, and energies are possible.

Heisenberg was “uncertain” Heisenberg Uncertainty Principle: it is fundamentally impossible and know precisely both, the velocity and position, of a particle at the same time. Impossible to assign fixed paths for an electron, like Bohr suggested.

FINALLY!! Erwin Schrodinger developed the QUANTUM MECHANICAL MODEL OF THE ATOM. Electrons are treated like waves, but the electron cannot be pinpointed in the atom. Instead the electrons are predicted to be in a 3D atomic orbital. And this is where we still are today.