The Structure of the Atom
Chapter 3
Chemistry: Matter and Change
Early Theories of Matter (3.1)
Democritus’s Ideas
1.
2.
3.
4.
Matter is composed of empty space through which atoms move
Atoms are solid, homogeneous, indestructible, indivisible
Atoms come in different sizes and shapes which creates different
properties
Changes in matter result from changes in groupings of atoms, not in
the atoms themselves
Dalton’s Atomic Theory (not completely true today!)
1.
2.
3.
Elements are made of tiny particles called atoms
All atoms of a given element are identical
Atoms of a given element are different from those of any other
element
4. Atoms of one element can combine with atoms of other
elements to form compounds
5. Atoms are indivisible and can not be created or destroyed in a
chemical reaction
http://web.visionlearning.com/dalton_playhouse/ad_loader.html
Subatomic Discoveries (3.2)
• JJ Thomson: Plum Pudding Model
– Uniform spherical cloud of positive charge with enough negative
electrons
• Robert Millikan: Electron Charge
• Rutherford: Nucleus and Protons
– Gold foil experiment – alpha (+) particles shot at gold foil surrounded
by a detection field, most of the particles passed through, but others
were deflected by the center of concentrated positive charge
• Rutherford and Chadwick: Neutrons
• http://www.brainpop.com/science/matterandchemistry/
Atomic Model
• http://phet.colorado.edu/en/simulation/rutherford-scattering
Subatomic Particles and the Nuclear Atom (3.23.3)
• Atom consists of:
1. nucleus – protons (+) and neutrons (0)
2. electrons (-) outside of nucleus
http://phet.colorado.edu/en/simulation/build-an-atom
Particle
Electron
Proton
Neutron
Relative Mass
1
1836
1839
Relative Charge
11+
0
**It’s the number and arrangement of electrons that
gives atoms their different chemical properties**
Isotopes (3.2-3.3)
http://www.brainpop.com/science/ matter and
chemistry/isotopes
– http://phet.colorado.edu/en/simulation/isotopes-andatomic-mass
• Atoms of the same element that contain the same number of
protons but have different mass numbers due to
different number of neutrons-isotope
Isotope Notations (3.2-3.3)
• Nuclear
A
Z
–
–
–
–
X
+/-
X = element symbol
A = mass number (protons +neutrons)
Z = atomic number (protons)
+/- = charge on the isotope (not on all isotopes)
• Hyphen
Element name/symbol – mass number
Example: Uranium-235 or U-235
Counting Atomic Particles (3.2)
• # protons = atomic number
OR
• # protons = mass number - # neutrons
• # neutrons = mass number - # protons
• Mass number = # protons + # neutrons
• (do NOT use the decimal number on the periodic table, that is the average
atomic mass based on the average of all the isotopes of that element)
• Electrons
– No charge: # electrons = # protons
– (+) charge: # electrons = # protons – charge
– (-) charge: # electrons = # protons + charge
Atomic Mass (4.3)
• The atomic mass of an element is the
weighted average mass of the isotopes of
that element.
• One atomic mass unit, or amu, is defined
as 1/12 the mass of a carbon-12 atom.