Atomic Theory
Greek Philosophy:
John Dalton:
Modern Atom:
Discovery
Democritus taught matter is made of indivisible particles. (BC 380)
Aristotle taught matter was ___________ and composed of mixtures of air,
earth, fire and water. (BC 340)
All matter is made up of tiny indestructible particles. These atoms cannot be created
destroyed or divided into smaller particles. (1809)
All atoms of an element are ________. Atoms of different element are different.
Chemical reactions are the _______________________________ of atoms.
They combine in specific proportions.
Smallest particle of an element that retains the properties of that
Technology
Conclusion
Cathode ray tube
Discharge tube
Discharge tube
Gold foil
bombardment
Gas discharge tube
Beryllium atom
alpha bombardment
element.
Year/Scientist
~1860 Crookes
1897 Thomson
1886 Goldstien
1911 Rutherford
1913 Bohr
1932 Chadwick
Subatomic particles
Particle
electron
proton
neutron
Charge
Symbol
Mass (g)
Location
Mass
(a.m.u.)
e-
9.02x10-28
~0
+
1.67x10-24
1
0
-24
1
p
n
1.67x10
Atomic number (Z): number of _____________ in the nucleus.
Mass number (A): total number of _________________________ in the nucleus.
 In a neutral atom the number of protons ______________ the number of electrons.
Isotopes: atoms of an element that have the same number of protons but a different number of
neutrons.
24
For Example:
12 Mg accounts for 79% of all the magnesium in nature.
25
12 Mg accounts for 10% of all magnesium.
26
12Mg accounts for 11% of all magnesium.
The average atomic mass for magnesium found on the periodic table is a weighted average of the
three isotopes: 24.31 g of Mg
Radioactivity: spontaneous decay of nuclei, releasing energy and subatomic particles
Radioisotopes: an unstable isotope of an element, which undergoes radioactive decay
 Not all isotopes are radioactive.
The Modern Atomic Theory
 All matter is made up of tiny particles called ______________. Each atom is made up of smaller
particles: ______________________________
 The atoms of one element cannot be converted into the atoms of any other element by a chemical
reaction.
 All atoms of one element have the same properties, such as _______________________.
These properties are different from the properties of the atoms of any other element.
 Atoms of different elements combine in specific proportions to form compounds.