Download Atoms - Mrs. Cox Physical Science Class

Atomic Structure
Chapter 4
4.1 Studying Atoms
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Democritus – believed all matter consisted
of extremely small particles that could not
be divided
Called these particles
Atoms
Atoms = word means
“indivisible”
Dalton – existence of Atoms
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Dalton proposed the theory that all matter is
made up of individual particles called atoms,
which cannot be divided
1803 - Atomic Theory of Matter
- All elements are composed of atoms
- All atoms of the same element have the same
mass, and atoms of different elements have
different masses
- Compounds contain atoms of more than one
element
- In a particular compound, atoms of different
elements always combine in the same way
Oops!
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Many “holes” (errors) were found in his
theories
But other scientists adjusted/corrected
what Dalton had done & went further
J.J. Thomson –
Subatomic Particles
& Charges
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1897 - Discovered positive & negative charged
particles with a gas-filled tube experiment
Plum Pudding model
(ex: Chocolate Chip Ice Cream)
negative particles are scattered
throughout the positive charged mass
= they balance each others charges
Sub-atomic Particles
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Thomson’s experiments provided the first
evidence that atoms were made of even
smaller particles
Protons =
+
positive (+ charge)
Neutrons = n
neutral (no charge)
Electrons = negative (- charge)
Rutherford
 1911
- Discovery of the Nucleus
 Gold Foil experiment - positive
charged of an atom is concentrated in
a small central area (the nucleus)
 According to Rutherford, all of an
atom’s positive charge is
concentrated in its nucleus
 Model of a large stadium w/ a marble
for the nucleus
4.2 Structure of Atoms
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Protons, electrons, and neutrons can be
distinguished by mass, charge, and location in
an atom
Three subatomic
particles exist:
Electrons =
(in electron cloud)
Protons =
+
(in nucleus)
Neutrons = neutral
(in nucleus)
P. 109 in text
Atomic Number & amu
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Atomic number = tells number of Protons
Atoms of different elements have a
different number of protons
Atomic Mass Number or Unit (amu) = the
sum of the protons & neutrons of an atom
Number of Neutrons =
amu – atomic number
Atomic #
amu