History of the atom UNIT 2

In the beginning… People believed: All matter can be divided into smaller parts without limits (there was no end)

Aristotle 384-322 BC A Greek philosopher, not a scientist Stated that all matter is composed of one substance, “hyle” (we are still not sure what hyle is) This statement was accepted until the 1600’s

Democritus 400 BC First person to adopt an atomic theory Stated everything was made of empty space and “atoms” Atoms – invisible particles

Dalton John Dalton 1766 – 1844 Considered the father of atomic theory and chemistry His law was called DALTON’S ATOMIC THEORY

Dalton’s Atomic Theory An element is made of atoms Atoms of an element are all alike Atoms can’t be created or destroyed Atoms of elements combine to form molecules and compound Atoms combine, separate, and rearrange in chemical reactions

Modern Atomic Theory Dalton’s theory has been modified into the modern atomic theory which we use today Only one exception to Dalton’s theory – atoms under special conditions may be divided. In other words, an atom can be fused apart into the particle which make up an atom (electrons, neutrons, and protons)

The Periodic Table Use this and your periodic table to answer the questions about the elements Atomic number Atomic Mass 8 15.9994 O Symbol Oxygen Name

Isotope Definition – An atom with the same number of protons but different number of neutrons The mass of an element is an average, due to the amount of isotopes that occur in nature Click on the link below then on the element listed and count the number of isotopes (just count the red symbols listed under isotopes) http://ie.lbl.gov/education/isotopes.htm

THE ATOM AND ITS PARTS

The diagram of the atom Electrons + - Protons Neutrons Nucleus

THE NUCLEUS The center of the atom Protons and neutrons reside in the nucleus The mass of the element comes from the nucleus

THE PROTON Symbol - p+ Discovered by E. Rutherford It has a positive charge which balances out the electron’s negative charge resides in the nucleus in the center of the atom It is the same as the atomic number on the periodic table – This is the number that makes the element what it is.

THE NEUTRON Symbol - n0 Discoverer - J Chadwick Has no charge The neutron also resides in the nucleus To calculate the neutron: Atomic mass rounded - # of protons

Electrons are the same as protons THE ELECTRON Symbol - e- Discover - JJ Thomson Has a negative charge The electron is like a hyperactive two year old, it moves very fast and circles the nucleus Electrons are the same as protons

Diagramming Elements Using your periodic table, the notes you just took, and your brain – fill in the chart