Download Dalton`s Atomic Theory

Dalton’s Atomic Theory
Democritus - Greek philosopher who
first suggested atoms
 John Dalton (1766-1844)
Studied ratios in which elements
combine
Dalton put together the first atomic
theory
Dalton’s Atomic Theory
All elements are composed of tiny indivisible
particles called atoms
Atoms of the same element are identical. The
atoms of any one element are different from
those of any other element
Atoms of different elements can physically
mix together or can chemically combine with
one another in simple-whole number ratios to
form compounds
Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of
one element, however, are never changed
into atoms of another element as a result of a
chemical reaction
Subatomic particles
Electrons (e-) - Negatively charged subatomic
particle
Discovered by J.J. Thomson in 1897
Used a Crook’s tube to run current through
gases
Beam was attracted to a magnet
Conclusion - beam is made up of small
particles he called electrons
Robert Millikan (1868-1953) first to calculate
electron mass - 9.11 x 10-28 g
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Subatomic particles
If a negative charged particle exist;
therefore, a positive particle must exist
as well. By 1920, the positive particle
had been confirmed.
Proton (p+) - positively charged
subatomic particle. Mass of 1.67 x 10-24
g
Subatomic particles
Neutron (no) - subatomic particles with
no charge
Discovered by James Chadwick (1891 1974) in 1932
Nearly same mass as a proton
Finding how many subatomic
particles for each atom
Atomic Number - whole number on p.t.
Gives the number of protons
Atoms are electrically neutral; there,
positives equal negatives.
Atomic number also equals number of
electrons
Finding how many subatomic
particles for each atom
Mass number = protons plus neutrons
Mass number = p+
+
no
Mass number is not found on the
periodic table
So, nO = mass number - p+
If carbon has a mass number of 14,
how many e-’s, p+’s, and no’s does it
have?
Symbols
Mass number is in top left and atomic
number is in bottom left
9Be
16O
8
4
How many subatomic particles in each?
Oxygen - 8 p+’s, 8 e-’s, 8 no’s
Beryllium - 4 p+’s, 4 e-’s, 5 no’s