The Atomic Nature of Matter

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Chapter 17

• The Atomic Nature of Matter

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Atoms

• Building blocks of matter
• Everything is composed of atoms

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Elements

• atoms of the same kind
• there are 115 known elements to date
• Every element is unique, and has its own set of
  properties
• All atoms of the same element have the same of
  protons.

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Atoms are recyclable

• the same atoms have been here since the beginning
  of time
• Combine w/ other elements, then go back to
  original form and back again
• You may be breathing the same air as Julius
  Caesar or George Washington.

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Atoms are very small

• Cannot view individual atoms w/ visible light
• Only way to see atoms is w/ Scanning Tunneling
  Microscope
• About 1023 (or 1000000000000000000000000000)
  atoms in one thimble-full of water

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Brownian Motion

• Jiggling of atoms
• Atoms are constantly moving
• Molecular motion never stops unless a substance
  is at a temperature of (-273 C) a.k.a. absolute
  zero

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Molecules

• combinations of atoms ex. H2, H2O, NaCl, N2
• Can be combinations of the same atom, or of
  different types of atoms

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Compounds

• combinations of atoms of different elements ex.
  NaCl, H2O, HCl
• A compound is always a molecule, but a molecule
  may not necessarily be a compound (examples .
  H2 , N2 )

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Rutherford Experiment

• Gold Foil - showed atoms are largely empty
  space, very dense nucleus that reflected charged
  particles backwards
• Like a shooting a 15-inch artillery shell at a
  piece of tissue paper and having it come back and
  hit you

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Nucleus

• very dense. Composed of Protons Neutrons
• Almost all of the mass of an atom is concentrated
  in the nucleus
• A teaspoonful of nuclei packed together would
  weigh a billion tons

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Neutrons Protons

• Nuetrons- Nuetral charged particle found in
  nucleus
• Protons- Positively charged particle found in
  nucleus, atoms of the same number of protons are
  atoms of the same element

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Isotopes

• for a given element, the number of neutrons may
  vary. Isotopes of an element are atoms of the
  same element having different numbers of neutrons
  
• Example - Uranium-238 (atomic mass 238) has
  isotope Uranium -235
• This was used to make the atomic bomb dropped on
  Hiroshima

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Electrons (e-)

• negatively charged particle not found in the
  nucleus.
• Orbits the nucleus in various energy levels.
• In a neutral atom, the number of electrons will
  match the number of protons
• of electrons in a neutrally charged atom is
  equal to the of protons, which is given with
  the atomic number.
• Mass of 1 electron is about 1800 times less than
  the mass of a proton or neutron

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Ions

• Charged Particle
• Positively charged (less electrons than protons)
• Negatively charged (more electrons than protons)
• not all atoms are neutral. This happens when the
  number of electrons is more than, or less than
  the number of protons.
• The number of protons never changes,
• however the number of electrons can change often.

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Shell Model of an Atom

• Electrons occupy different shells.
• 2 maximum electrons may fit in the first shell
• The next shell holds 8 electrons, and the largest
  shell will hold 32 electrons.
• For example, if an atom has 13 electrons, it will
  have 2 in the first shell, 8 in the second shell,
  and the remaining 3 will go in the third shell.

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Periodic Table

• chart that lists atoms by their atomic number and
  by their electron arrangement.
• As you move from left to right on chart each
  element gains one proton and electron .
• As you go down each column each element has one
  more shell filled than the element above.
• Elements in the same column are in a Group.
  Groups have similar properties.

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• Atomic Number - number of protons in the nucleus
• Atomic Mass equals the average mass (in atomic
  mass units) of the nucleus
• of Protons Atomic Number
• of Electrons of Protons, (if molecule has
  no charge)
• of Neutrons (Atomic mass (rounded)) -
  (atomic number)

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Phases of Matter

• Solid, Liquid, Gas three familiar states of
  matter. In all phases, atoms are in constant
  motion.
• The more the molecules move the more fluid they
  become,
• Solid molecules have least energy, stay fixed
  relative to each other
• Liquid- molecules have more energy, molecules
  move relative to one another
• Gas molecules have most energy, move with large
  distances between each other

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Plasma the 4th State of Matter

• Consists of positive ions and free electrons.
  Exists only at high temperatures.
• What sun and stars are made of. Can be seen here
  on Earth in the glowing gas of fluorescent lamps.