Atomic Structure
Theories
9 SCIENCE
Dalton’s Atomic Theory
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All Matter is made up of small particles called
atoms.
All atoms of a particular element are identical in
mass and size BUT are different from atoms of
another element.
Compounds are created when different elements
are combined chemically
Atoms cannot be created or destroyed or broken
down into simpler particles
He thought an atom was an indivisible sphere like a
billiard ball (pool ball)- an atom can’t be broken
down any farther
Thompson’s Atomic Theory
All atoms are made up of small subatomic
particles (protons and electrons because they
are smaller than atoms) particles called protons
and electrons.
 All protons are identical, all electrons are
identical but different from each other
 Electrons= negative charge
 Protons= positive charge
 Protons have more mass
 Atoms contain both protons & electrons- they
have no charge
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Thompson’s model:
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Plum Pudding Model:
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Pudding is positively charged dough, with
negatively charged electrons (raisins)
throughout.
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Ex. Muffin- with little effort, you can take out the
raisins (electrons)
Bohr’s Atomic Theory
Atom consists of a nucleus (tiny core that is very
small volume but dense compared to the rest of
the atom)
 Nucleus contains protons
 Atoms consists of an electron cloud around the
nucleus ( larger in volume but less dense and
lighter than nucleus- its also negative)
 Believed electrons are located outside the
nucleus
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Bohr’s Model:
1st shell- maximum of 2 electrons
2nd shell- maximum of 8 electrons
3rd shell-
Bohr- Rutherford’s Atomic Theory
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Nucleus consists of protons (positively charged
subatomic particles) and neutrons ( neutral, no
charge)
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Electrons are outside of the nucleus but are
found in orbitals (paths) around the nucleus
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The dotted lines are orbitals which are just paths
the electrons travel around the nucleus
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Nucleus- dense, contains protons& neutronstakes up less space compared to the rest of the
atom
Bohr –Rutherford continued…
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This model is the one that we believe in today
and its important to note that if we believe in this,
then we disregard what Dalton said about the
atom being the smallest particle of matter (we
know that it contains protons,
electrons,neutrons). However, Dalton
was correct when he said that all atoms of one
element are different than the other atoms of
another atom.
Questions to do (use your book)
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Define: law, theory, chemical formula, molecule,
periodic table
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How did the elements get their symbols?
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List the properties of metals, non-metals and metalloids
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How did Mendeleev build his periodic table?
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Read pages 183-186, 190-194, 203-204 and 216-217