SCIENCE 1101: SCIENCE, SOCIETY and the ENVIRONMENT I

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SCIENCE 1101 SCIENCE, SOCIETY and the
ENVIRONMENT I

• Lecture 7

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Introduction to Matter

• Everything in the Universe is composed of matter.

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Matter in the Universe

• There are 92 naturally occurring elements. More
  have been made artificially in the lab but these
  are unstable.
• About 25 of the 92 natural elements are known to
  be essential to life.
• 4 elements make up 96 of living organisms
• Hydrogen, Carbon, Nitrogen, Oxygen

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Matter in the Universe

• 90 of the Universe is composed of Hydrogen and
  Helium.
• Stars are giant fusion reactors forcing atoms to
  fuse together due to gravity at the center of the
  star. Therefore, all of the matter in the
  universe has been created in the centers of stars.

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Introduction to Matter

• The ancient Greek philosophers thought that the
  great variety of matter arose from 4 basic
  ingredients
• Air
• Water
• Fire
• Earth

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Introduction of Matter

• These substances were thought to be pure and not
  able to be broken down into anything else.
• All other substances were thought to be formed by
  blending various portions of two or more of these
  elements.
• They had the right idea but the wrong elements.

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Introduction to Matter The Cheese Argument

• In the 5th century Democritus (a Greek
  philosopher) argued that substances can be
  separated to a smallest piece.
• e.g. Cut a piece of cheese with a sharp knife,
  then cut one of the pieces left, then cut one of
  those pieces, etc., etc. you will eventually get
  to the smallest piece that cant be cut further.
  He called this the ATOM (That which cannot be
  divided).

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Introduction to Matter Dalton

• In the early 1800s, John Dalton, through lab
  experiments, found that most substances can be
  broken down into another, but a few could
  not.Gold, Sulfur, Iron.
• These substances he called Elements Substances
  that cannot be broken down into other substances
  by chemical reactions

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Introduction to Matter

• Dalton guessed that each element was represented
  by its own atom, which are different from the
  atoms of any other element.
• Today we recognize 92 elements that occur
  naturally.

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Introduction to Matter

• Each element has a name, which is abbreviated by
  a one or two letter abbreviation
• For example O Oxygen, H Hydrogen, Ca
  Calcium, etc.
• These atoms can combine to form other substances.
  2H 1O H2O Water

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Introduction to Matter

• Two or more atoms that are combined will form a
  Molecule.
• Two or more different elements can combine in a
  fixed ratio to form a compound

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The Debate

• Throughout the 19th and early 20th century
  scientists debated whether atoms were physically
  real or just a useful idea.
• The problem was that atoms were too small to see.
  Therefore it was hard to argue either way.

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The Debate

• Albert Einstein ended the debate in 1905 when he
  explained a phenomenon called Brownian Motion.
• In 1827, Dr. Robert Brown noticed that when
  pollen grains were observed under a microscope,
  they moved for no apparent reason.

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The Debate

• No one could explain why this was happening until
  Albert Einstein explained it.
• Simply, Einstein argued that the movement was
  caused by collisions with atoms. If atoms were
  imaginary, atoms couldnt cause motion, therefore
  atoms must be real.

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The Atom

• Now we know that all matter is made up of atoms.
  Making atoms the building blocks of matter.
• An atom is the smallest possible amount of an
  element that keeps the properties of that element.

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The Atom

• Atoms are made up of 3 types of smaller particles
  called sub-atomic particles
• Proton
• Neutron
• Electron

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The Atom

• Protons and Neutrons are found at the center of
  the Atom. The Electron orbits the neutrons and
  protons near the speed of light.
• The differences we see in the different elements
  is due to the the number of subatomic particles
• For example Hydrogen has 1 proton and 1
  electron, Calcium has 20 protons, 20 neutrons and
  20 electrons.

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Structure of the Atom

• The Nucleus
• Contains 99.9 of the atoms mass.
• Composed of Neutrons and Protons
• The nucleus overall has a positive charge.
• Protons
• Has a positive charge
• Determines how the element will behave, therefore
  each chemical element is defined by its number of
  protons.

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Structure of the Atom

• Atoms are classified by their atomic number,
  which is equal to the number of protons in its
  nucleus.
• Neutron
• Has no electrical charge
• Has little effect on how the atom acts or its
  structure
• However, the Neutron holds the nucleus together

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Structure of the Atom

• Electron
• Mobile, Constantly in motion
• Carries a negative charge
• VERY small
• Weighs 1/1860th as much as the Proton or the
  Neutron.
• The number of electrons must equal the number of
  protons to maintain electrical neutrality

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Structure of the Atom

• Therefore atoms are generally considered neutral
  unless a chemical reaction causes a change in
  that charge.
• i.e. an electron is taken away or gained
• If an atom has gained or lost an electrons, and
  therefore has an electrical charge, it is called
  an ion.

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The Periodic Table

• A table that ranks all of the Atoms according to
  their weight.
• More Protons and Neutrons means more weight.
• Dmitri Mendeleyev made the first table in 1869.
  He organized the elements according to their
  weight.
• He noticed that their chemical properties were
  somehow related to their weight (but he couldnt
  explain it).

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The Periodic Table

• In the Periodic Table, atomic numbers increase
  from left to right.
• The Atomic Number is defined as the number of
  proton in an atom.
• The elements in the same column have similar
  chemical behavior, meaning they enter into
  similar reactions and combine to form similar
  compounds.

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Models of Atoms

• Early models of the atom thought of the electron
  as orbiting the nucleus very much like planets.
• However, this model doesnt work because it
  violates the laws of thermodynamics.

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Models of the Atom

• An accelerated electrical charge must give off
  electromagnetic radiation
• This energy has to come from somewhere, so the
  electrons would spiral into the nucleus to
  maintain energy conservation

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Models of the Atom

• Today we know that the elements are grouped into
  rows and column because of the way electrons fit
  around the nucleus.
• Unlike planets orbiting the Sun, Electrons have
  specific orbital distances.
• There are certain allowed orbits located at
  specific distances from the nucleus in which an
  electron can exist for long periods of time
  without giving off radiation.