A-TO-MIC MODELS

While various types of microscopes can reveal details at many levels of magnification, no microscope can produce images showing the detailed parts of single atoms. For understanding atoms at this level, we traditionally use models instead of actual images.

The models presented in this investigation show a highly simplified view of atoms, but they serve the purpose of allowing us to examine the number of protons, neutrons, and electrons in common elements.

Now a brief history of the first Atomic Models.

EARLY GREEK THEORIES


In 400 B.C., Democritus thought matter could not be divided indefinitely. And this led to the idea of atoms in a void.
In 350 B.C., Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. He was wrong, however, his theory persited for 2000 years.



JOHN DALTON

In the 1800's Dalton proposed a modern atomic modelbased on experimentation not on pure reason.

•All matter is made of atoms.
•Atoms of an element are identical.
•Each element has different atoms.
•Atoms of different elements combine in constant ratios to form compounds.
•Atoms are rearranged in reactions.

His ideas account for the law of conservation of mass (atoms are neither created nor destroyed) and the law of constant composition (elements combine in fixed ratios).



BOHR

•Electrons orbit the nucleus in “shells”
•Electrons can be bumped up to a higher shell if hit by an electron or a photon of light



There are 2 types of spectra: continuous spectra & line spectra. It’s when electrons fall back downthat they release a photon. These jumps down from “shell” to “shell” account for the line spectra seen in gas discharge tubes (through spectroscopes).

So...What are atoms?
Atoms are the basic building blocks of matter that make up everyday objects. A desk, the air, even you are made up of atoms!
There are 90 naturally occurring kinds of atoms. Scientists in labs have been able to make about 25 more.
Atoms are made of three basic particles:
Protons, which carry a positive charge.
Neutrons, which carry no charge.
*Protons and Neutrons are join together to form the nucleus, the central part of the atom*
Electrons, which carry a negative charge.

The nucleus of an atom is extremely small in comparison to the atom. If an atom was the size of the Houston Astrodome, then its nucleus would be the size of a pea.

"ATOMS ARE EVERYWHERE!!"