9/11/2012
1
UNIT 3
ATOMIC STRUCTURE
Mrs. Medina
1
Early Models of the Atom
•All matter is composed of tiny
fundamentals particles
–ATOMS: smallest particles of an element
that retain the identity of the element in
a chemical reaction
2
•Greek philosopher (~400
BC) suggested existence of
atoms
–He claimed atoms were
tiny, indivisible, and
indestructible
•His ideas agree with
modern theory but they
were not based on
scientific experiments.
3
Democritus’s Atomic Philosophy
Dalton’s Atomic Theory
•John Dalton (1766-1844),
–English chemist and
schoolteacher.
•He used experimental methods
and transformed Democritus’s
ideas about atoms into
scientific theory.
–He studied the ratios in which
elements combine
–He formulated an atomic
theory. 4
Dalton’s Atomic Theory
1. All elements are composed of tiny indivisible
atoms
2. Atoms of the same element are identical and
atoms of different elements are different.
3. Atoms of different elements can mix
physically or chemically in whole-number
ratios to form compounds.
4. Chemical reactions occur when atoms are
joined, separated or rearranged.
5. Atom of one element can never became an
atom of another element during a chemical
reaction.
5
Sizing up the Atom
•Atoms are around
1 x 10-10 meters in size.
–Line up 100,000,000
copper atoms side by side,
they would only produce a
1 cm long line.
–A copper penny contains
about 2.4x1022 atoms.
–Earth’s population = 6x109
•Atoms can be seen with a
scanning tunneling
microscopes
