atomic theory -...
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Atomic Theory
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460 BC Democritus develops the idea of atoms
He pounded up materials in his pestle and
mortar until he had reduced them to
smaller and smaller particles which he
called
ATOMA
(Greek for indivisible)
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Scientist What He Discovered Date
John Dalton
J.J. Thomson
Ernest Rutherford
Niels Bohr
James Chadwick
Modern Electron Cloud Model
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John Dalton – 1600’s
Elements are composed of one TYPE of atom
An atom of one element cannot be changed into an atom of a different element
Atoms can only be re-arranged,notdestroyed or created
Atoms from different elements form compounds.
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J.J. Thomson – 1897
Atoms have subatomic particles within them
Atoms contain negatively charged particles so must have positive charges also
Model looked like a solid mass with negatively charges embedded in it – called electrons
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Ernest Rutherford - 1910
Used the Gold Foil Experiment – Page 104
There is a nucleus in the atom Nucleus make up most of atom’s mass
and electrons move around it Positive particles exist and named
protons
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Niels Bohr - 1913
Student of Thomson and Rutherford Electrons could only have specific
amounts of energy in energy levels Electrons must move in orbits
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James Chadwick - 1932
• New particle discovered with about the same mass as proton called neutrons
• Neutrons have no electrical charge
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Electron Cloud Model – 1920’s
Electrons form a “cloud” as they move around the nucleus
An electron’s movement is related to its energy level
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• Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
• first shell a maximum of 2 electrons
• second shell a maximum of 8 electrons
• third shell a maximum of 18 electrons
•Fourth shell a maximum of 32 electrons
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In Other Words, It’s All About The Electrons!!!
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Use Graphic Organizer
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Atoms
• Smallest unit of matter
•Have subatomic particles
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Structure of Atoms
• Nucleus – contains most of the mass of atom (protons and neutrons)
• Energy shells – contains electrons
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Atomic Charges
• Protons – have positive charge
• Neutrons – have no charge
• Electrons – have negative charge
• Isotopes – have extra neutrons
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Electrons• Very small, little mass
• Have negative charge
• Forms a “cloud around the nucleus of atom
Electrons orbit nucleus
Energy shells hold electrons
valance electrons are in outer shell hat interact with other atomic electrons
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Protons
• Makes up part of mass in nucleus
• Has positive charge
• Is called the atomic number
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Neutrons
• Makes up part of mass in nucleus
• Has no charge (neutral)
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Electrons
O Each electron shell can hold
a certain number of
electrons
O Electron shells are filled
from the inside out
O Noble gases have full outer
electron shells
O All other elements have
partially filled outer electron
shells
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ElectronsO Electrons are always
moving. They spin very quickly around the nucleus of an atom.
O As the electrons zip around, they can move in any direction, as long as they stay in their shell.
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Atomic Mass and Number
Size and Scale
• Atoms are mostly empty space
• The tiniest speck of dust may contain 10 billion atoms.
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Size and Scale of Atoms
• To give you an idea of the scale of an atom, picture an empty baseball stadium, like Turner Field
• If the nucleus (the size of a pencil eraser) is on the pitcher’s mound, where would the electrons be?
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Size and Scale of Atoms
• In the top row of seats!
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Atomic Number• Every atom of an element has the same
number of protons
• The atomic number identifies the element and its placement on the table.
• number of protons in the nucleus of an atom
• Is equal to number of electrons of an atom
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Isotopes and Atomic Mass• Atoms with the same number of protons, but
a different number of neutrons are called isotopes.
• Isotopes are identified by its mass number
• Atomic mass is the sum of protons and neutrons in the nucleus
• Examples
of Isotopes: