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introduction to atoms


smallest particle which an element can be divided and still be the same substance. they make up elements.and they are called the BUILDING BLOCKS OF LIFE.(elements combine to form compounds).Diamter (3 hundred-millionths)


unifying explanation for a broad range of hypotheses and observations,supported by testing.


proposes atom(uncuttable part of something).
Aristotle disagrees.

John Dalton

creats atomic theory;revised as new info is found.

Dalton's atomic theory

1.all substances made up of atoms.atoms are small particles that cannot be created,divided or destroyed.
2.atoms of same elements are identical, atoms of diff. elements are diff.
3.atoms join with other atoms to form new substances.


small particles inside an atom, negative charge.(-)
they are located on the electron clouds/levels/shells.


used a gold foil experiment to discover there was a small massive thing inside of an atom.


the center of an atom. (Most of the atom is made up of electron clouds.)most mass is found in the nucleus connection to the neutrons & protons.


said that electron can jump from level to level,but they have definite paths.


exact path of an electron cannot be predicted therefore we call them e-clouds.

50,000 Al atoms to equal the thickness of :

sheet of aluminum foil.(penny contains 2x10^22 atoms).

Inside of an atom:

(+) is its charge.
to find the # of proton we look at the atomic # located in upper right .


(-)is its charge.


located:outside of the nucleus in electron cloud or shell.
(-)is its charge.
to find the # of electron =# of proton.


an atom that has gained a charge to the loss or gain of an electron.


-an atom with the same # of protons(so still the same element) but diff.# of neutrons.
-some are unstable so they are radioactive.
-most isotopes share same properties.

Atomic mass

weighted average of all the naturally occurring isotopes so this explains why it is a nonradioactive.

4 forces keep atoms together:

most familiar force , but it is very small.

2)electromagnetic force

unlike charges attract , and like charges repel.

3)strong force

proton pushing away from each other, but this force keeps the nucleus together.

4)weak force

important in radioactive atoms, plays a role in a neutron changing into a proton.

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