P. Sci.

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P. Sci.

• Unit 8
• Chapter 4
• Atoms

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Atomic Structure timeline

• Ancient Greece - Democritus proposed the atom a
  tiny solid particle that could not be subdivided.
• 1904 J.J. Thomson discovered that atoms
  contained small, negatively charged particles
  called electrons.

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• 1911 Ernest Rutherford proposed that the atom
  had two parts the nucleus in the center (most
  of the mass) surrounded by the electrons.
• 1913 Niels Bohr
• hypothesized that
• electrons traveled in fixed
• orbits around the atoms nucleus.

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• 1913 James Chadwick concluded that the
  nucleus contained positive protons and neutral
  neutrons.
• 1926 Erwin Schrodinger developed the quantum
  mechanical model which is based on the wavelike
  properties of the electron. (not a particle
  leads to quantum physics)

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• 1927 Werner Heisenberg (the Heisenberg
  uncertainty Principle) described that it is
  impossible to know precisely both an electrons
  position and path at a given time. Led to the
  electron cloud theory.

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Atoms

• The smallest particle that has the properties of
  an element.

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Daltons Atomic Theory

• Every element is made of tiny, unique, particles
  called atoms that cannot be subdivided.
• Atoms of the same element are exactly alike.
• Atoms of different elements can join to form
  molecules

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Parts of an Atom

• Nucleus small, dense center of an atom made up
  of 2 subatomic particles that are almost
  identical in size and mass.
• Protons have a
• positive charge
• Neutrons have no charge

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Parts of an Atom cont.

• Electrons are tiny particles that have very
  little mass that moves around the outside of the
  nucleus. These particles are negatively charged
  and form a
• cloud around
• the nucleus.

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• The number of protons and electrons an atom has
  is unique for each element.

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Atomic Charge

• Atoms have no overall charge because the protons
  () cancel out the electrons (-).

Helium 2 protons - 2
2 neutrons - 0 2 electrons
- -2 total charge 0
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Protons

• positive () charge
• Found in the nucleus
• of protons atomic
• The number of protons identify the element
  (atomic )

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Neutrons

• no charge
• Found in the nucleus
• Along with protons makes up atomic mass
• protons and neutrons are made up of quarks
  which three quarks determines whether it
  becomes a proton or a neutron.

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Electrons

• negative () charge
• travel in orbitals (or energy levels) around the
  nucleus. (electron cloud)
• valence electrons - the of electrons in the
  outer shell oxidation

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• Unit of measure for atomic particles is Atomic
  mass unit (amu) protons and neutrons about 1
  amu (electrons are about the size of 1 quark)

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Chemical symbols

• The one or two letter abbreviation of the element
  name.

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Mass Number or Atomic Mass

• the sum of the number of protons and the number
  of neutrons in the nucleus of an atom.
• of neutrons
• mass - atomic

Neutrons
Protons
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Average atomic mass

• the weighted - average mass of the mixture of all
  an atoms isotopes. The average atomic mass is
  close to the mass of its most abundant isotope.

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Isotopes

• Atoms of the same element that have a different
  of neutrons. (identified by the element name
  followed by the mass )
• ex. C-12, C-14, B-10, B-11)

Carbon 14 8 neutrons
Carbon 12 6 neutrons
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The End
For now