Modern Atomic Theory

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Modern Atomic Theory
Grade 9 Science Chemistry
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Modern Atomic Theory

• Atoms are made of 3 particles protons, neutrons
  and electrons
• Atoms have a nucleus that is made of protons and
  neutrons with electrons orbiting around it.
• Protons and electrons have opposite charges,
  therefore, they attract.
• This attraction holds the electrons around the
  nucleus.

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Elements vs. Compounds

• An element is a pure substance made up of one
  type of particle, or atom. Each element has its
  own distinct properties and cannot be broken down
  into simpler substances by means of a chemical
  change.
• Compounds are pure substances that are made up of
  two or more elements chemically combined
  together. They can be broken down into elements
  again by chemical means.

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Difference Between Theories and Laws

• Laws do not explain anything . They just
  describe and summarize what happens.
• Theories are imaginative ways to explain why
  something happens.

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Democritus
Around 400 BC, a Greek philosopher named
Democritus suggested the first atomic theory He
explained that all things are "composed of
minute, invisible, indestructible particles of
pure matter which move about eternally in
infinite empty Even though there was no
technology to help research Democrituss theory,
he was very precise John Dalton, J.J. Thompson,
Ernest Rutherford, Niels Bohr, and Ernest
Schrodinger all contributed significantly to the
modern atomic theory by finding the actual
evidence.
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John Dalton

• Lived from 1766-1844
• Was one of the earliest scientists to contribute
  to the modern atomic theory.
• Daltons Theory  
• All elements are composed of atoms.
• All atoms of the same element are identical in
  particular they have the same mass.
• The atoms of one kind of element are different
  from the atoms of all other elements - in
  particular the atoms of one element have a
  different mass than those of other elements.
• Atoms are indestructible and retain their
  identity in chemical reactions.
• Compounds are formed by joining atoms in specific
  whole number ratios.

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J.J Thompson
Lived from 1856-1940 Won a noble prize for his
great work on the electron. Realized that if
there ware negative parts to atoms, then there
must be positive parts as well to balance it,
because most matter is neutral. His theory of
electron distribution inside an atom was later
proved to be incorrect by Ernest Rutherford. In
1897,discovered first subatomic particle, a
component of all atoms, the electron
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Ernest Rutherford
Lived from 1871 1937 Made blueprints of an
atom. Said to be the father of nuclear
physics. Said that radiation was caused by the
destruction of atoms and that the alpha particle
is the helium nucleus.
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Niels Bohr
Lived from 1871 - 1937 Discovered the proton in
1910 Won the 1922 Nobel Prize for physics,
mainly for his work on the structure of atoms
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Erwin Schrodinger
Lived from 1887 to 1961 Viewed electrons as
continuous clouds Introduced "wave mechanics" as
a mathematical model of the atom.