Atomic TheoryHow We Got Where We Are Today

Robert ErwinUMS Rockwall ISD2014 - 2015

March through History of Atomic Theory

Man has been interested in the makeup of matter and the universe throughout history.

He has created some really cool ideas and legends about how stuff was created and manipulated, but the process to look at the nature of matter was slow to evolve.

Can you name any legends or theories?

Democritus ~ 430 B.C.

Greek philosopher from Thebes Known as the laughing philosopher. Came up with the idea that all stuff can be

broken down into pieces too small to see, but are still the original stuff, but all are made of the same material.

Called these pieces “ATOMOS”, or uncutable.

March through History of Atomic Theory Then……….Mostly nuthin’ for many

centuries. Why do you think that is?

John Dalton - 1803

British Chemist came up with idea that everything is made up of atoms that cannot be divided or destroyed.

Believed atoms are solid spheres. Also known as the “Bowling Ball” theory. Different atoms have different

masses and sizes. Atoms combine to create

compounds.

Dimitri Mendeleev - 1869

Russian scientist who categorized the known elements.

Accurately predicted elements that had not yet been discovered.

Created the Periodic Table of the Elements.

J.J. Thomson - 1897 English chemist who determined the

atom was made up of subatomic particles.

Came up with concept of charged matter (positive) and electrons (negative).

Thought the negative electrons were mixed together in a positively charged atom.

Model looked like raisins in a pudding bowl, so known as the “plum pudding” model.

Ernest Rutherford – 1909 to 1912

New Zealand Scientist came up with the idea of a nucleus within the atom.

He concluded that Electrons stayed outside the nucleus, but their exact location cannot be predicted.

Nucleus was made up of Protrons, or positively charged particles.

His model was called the “Solar System” model.

Niels Bohr - 1913

Danish physicist who explained how electrons move.

Created a model we still use today to understand basic atomic structure. We will use this model in great detail very shortly.

Electrons move between shells Shells based upon energy levels

Erwin Schrodinger - 1924

Austrian physicist came up with idea that exact locations of electrons cannot be predicted, so represented in an electron cloud surrounding the nucleus.

Provided the mathematical formula wave equation to accurately explain his ideas of how energy levels of atoms behave.

James Chadwick - 1932 English physicist who came up with

the idea of Neutrons in the nucleus.

This explained differences in mass of atoms of the same element.

Neutrons have no electrical charge.

Assigned the Atomic Mass Unit (AMU).

Enrico Fermi - 1942

Italian physicist created the nuclear reactor and conducted first controlled nuclear chain reaction.

Considered with Robert Oppenheimer to be one of the fathers of the atomic bomb.

Modern Theory Atom is the smallest unit of an element.

Made up of three main particles Proton (+) positively charged Neutron (0) No Charge Electron (-) Negatively charged

Almost all of the mass of an atom is in its nucleus Proton = 1 Atomic Mass Unit Neutron = 1 Atomic Mass Unit Electron = 1/2000

th Atomic Mass Unit Add the Protons and Neutrons to get the

Atomic Mass.

Modern Theory Protons and Neutrons are in the nucleus Electrons exist outside the nucleus in the

electron cloud. The # of Protons = the # Electrons in a

neutral atom.

Modern Theory - Protons

Protons are in the nucleus Protons have a mass of 1 AMU The # of Protons in an atom determine

what element it is. (Ex: If an atom has exactly 3 protons, it is ALWAYS Lithium)

The # of Protons in an atom is also = its Atomic Number.

Modern Theory - Neutrons

Neutrons are in the nucleus Neutrons have a mass of 1 AMU The # of Neutrons will usually be close to

the # of Protons – but not always exactly the same. (Ex: Lithium has 3 Protons but 4 Neutrons)

Modern Theory - Electrons

Electrons circle the nucleus in a cloud Electrons have a mass of 1/2000

th AMU The # of Electrons will = the # of

Protons in a stable atom. (Ex: Lithium has 3 Protons and 3 electrons)

Valence Electrons are the outermost electrons.

Valence Electrons determine an atom’s reactivity (how it behaves).

Modern Theory

And…..TaDa!!!!!! Now we have the tools and procedures to more accurately understand atom behavior, so we can better learn to use them to our benefit.