The ATOM

A History of the Atom as brief as possible Democritus – matter can be divided – coined ‘atom’ Aristotle – matter is continuous Jump to 1700’s Mendeleev – organized periodic table Dalton – measured pure substances Rutherford – discovered nucleus Bohr – found pattern with atomic number Schrodinger – movement of electrons Planck and Heisenberg – nuclear chemistry

What the Heck? Atom comes from the Greek word meaning indivisible. Today we know that what we once knew as the atom, the smallest particle of life, is in fact divisible and contains smaller particles The Electron, Proton and Neutron

In an Atom: Protons and Neutrons are in the Nucleus Electrons are in the Electron cloud or energy levels.

In the Atom: Nucleus is positively charged in the center of the atom Electron cloud is negatively charged area surrounding the nucleus

To Illustrate

Dalton’s Laws Still followed to this day: Law of conservation of mass: matter cannot be created or destroyed in ordinary chemical or physical changes Law of definite composition: a chemical compound contains the same elements in exactly the same proportions regardless of the size of the sample or the source

Modern Atomic Theory 1) All Matter is made up of very small particles called atoms 2) Atoms of the same element have the same chemical properties 3) While individual atoms of a given element may not all have the same mass any sample of the element will have a definite average mass that is characteristic.

Modern Atomic Theory Cont. 4) Compounds are formed whenever two or more elements unite, with each atom loosing its characteristic properties as a result of the combination 5) Atoms are not subdivided in physical or chemical reactions

Protons, Neutrons and Electrons Atomic Number = # of protons = # of Electrons Atomic weight = # of protons + # of neutrons

So if you had an atom of Lead Atomic Number of lead = 82 Protons = 82 Electrons = 82 Atomic Mass of Silicon = Neutrons = Mass-Protons = = 125

Use Your Periodic Table NameSymbolAtomic Mass ProtonElectronNeutron Si Iron Bi Zinc

Masses of Subatomic Particles Proton x g Neutron x g Electron x g Electrons are 10,000 times smaller than Protons and Neutrons!

Isotope Isotope - atoms with the same number of protons but different numbers of neutrons. Number of protons make up the identity of the atom. I.E. anything with 6 protons is Carbon.

And why is the mass number a decimal? Carbon: (2 natural isotopes) Carbon (total weight = 12) (98.89 percent of Carbon atoms) Carbon - 13 (total weight = 13) (1.11 percent of Carbon atoms) (12 x.9889)+(13 x.0111) = the atomic mass of Carbon

Where the heck did that equation come from? (12 x.9889) + (13 x.0111) = (12 x.9889) the weight of Carbon - 12 times the percent of Carbon - 12 (13 x.0111) the weight of Carbon - 13 times the percent of Carbon - 13

Try it yourself: Neon - 22 (Total weight = 22) (10% of Neon) Neon - 20 (Total weight = 20) (90% of Neon)

Once More: Hf = 5% Hf = 19% Hf = 27% Hf - 179= 14% Hf = 35%