CHEMISTRY BASICS

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The Atom Its Structure
S. Staron 2-11
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• Think about sugar crystals. You know that they
  are small crystals and every crystal is
  identical.
• You may grind these
• particles into a very
• fine powder, but each
• tiny piece is still sugar.
• If you dissolve the sugar in water,
• the sugar particles become
• virtually invisible.

From Philosophy to Science
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• You could even look at the sugar solution under a
  microscope and youd still not be able to see
  the sugar.
• However, you know it is still there - you can
  taste it.
• These observations and logical patterns led
  philosophers and scientists to ponder the design
  of the particles that make up everything.

From Philosophy to Science
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• By the 1800s it was determined that atoms are
  actually composed of several basic types of
  smaller particles.
• It is the number and arrangement of these
  particles that determine the atoms chemical
  properties.

From Philosophy to Science
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• A new definition of an atom emerged
• The smallest particle of an element that retains
  the chemical properties of that original element.

Atomic Structure
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Copper atoms on silica surface.
Distance across 1.8 nanometer (1.8 x 10-9 m)
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• All atoms consist of 2 regions of subatomic
  space
• The nucleus
• The electron cloud

Atomic Structure
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electron e- -1 0 Cloud
proton P 1 1 Nucleus
neutron N 0 1 Nucleus
Properties of Subatomic Particles
MASS
REGION
CHARGE
SYMBOL
NAME
FOUND
Atomic Structure
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Nucleus

• The nucleus is a very small region located near
  the center of the atom.
• The nucleus contains at least 1 proton, which is
  positively charged, and usually 1 or more
  neutral particles called neutrons.

Atomic Structure
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Nucleus

• The Periodic Table lists atoms in consecutive
  order by the number of protons (atomic number).
• Atoms of different elements have different
  numbers of protons, so the atomic number
  identifies the element.
• Atomic 47 can only be Ag (Silver) because it
• has 47 protons in each nucleus.

Atomic Structure
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Nucleus

• The nucleus is a densely packed cluster of
  protons, which are all electrically positive.
• Wait! Dont like charges repel?
• When 2 protons are very close to each other,
  there is a strong force of attraction between
  them.
• A similar attraction exists
  between 2 neutrons.

Atomic Structure
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Nucleus

• These short-range, strong nuclear forces
• hold the nucleus together.
• When these nuclear forces are
• strong enough the atom is stable.
• If the forces are not strong enough
• (in heavier atoms) the atom is
• unstable and is radioactive.

Atomic Structure
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Nucleus

• The total number of protons neutrons determines
  the mass of the atom. This is called the Mass
  Number.
• A carbon atom, has 6 protons and 6 neutrons,
  so its mass number is 12
• P N Mass number
• -OR-
• mass number
• _- atomic number
• number of neutrons.

Atomic Structure
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Nucleus

• All atoms of hydrogen have one proton, but not
  all weigh the same. Most have no neutrons, some
  have one and a few have two.
• These are called isotopes of each other. If we
  add up all the isotopes and divide to get the
  average, this is the number on the PT. It is the
  atomic weight.

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Nucleus

• The decimal number on the PT the atomic weight.
  If we round that number, we get the mass number
  the whole number mass of an average atom.

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Atomic Mass Units (amu)

• We don't normally use grams for measuring the
  mass of an atom. It's much more convenient to use
  something called the atomic mass unit, or amu.
  That's approximately the mass of one proton or
  neutron.
• Many versions of the periodic table give the
  weights of the elements in amu these are average
  weights, taking into account the different
  isotopes that exist.

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amu

• One gram is about 600 sextillion
  600,000,000,000,000,000,000,000 amu (that's a 6
  followed by 23 zeros).
• A pound is just shy of 300 septillion amu--that
  is, 300,000,000,000,000,000,000,000,000. (26
  zeros there.)
• This is why we use amu's instead of grams.

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amu

• What about the mass of the electron?
• Electrons are so light that you can usually
  ignore their mass relative to the atom as a
  whole.
• A proton has about 2000 times the mass of an
  electron.

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In Review

• Atomic number of protons
• Mass Number Protons Neutrons
• An electrically neutral atom has
• protons electrons

Atomic Structure
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• Because atoms are neutral, we know
• protons electrons.

Atomic Structure
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Electron Cloud

• The electron cloud is the region that
  surrounds the nucleus .
• This region contains one or more
• electrons, which are negatively charged
  subatomic particles.
• The volume of the
  electron cloud is much
  larger than the nucleus.
• (10,000 times as big!)

Atomic Structure
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Electron Cloud
Electrons are arranged in energy levels or
shells around the nucleus of an atom.
First shell can hold a maximum of 2
electrons Second shell can hold a maximum of 8
electrons Third shell can hold a maximum of 8
electrons
ATOMIC STRUCTURE
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Electron Cloud
First shell holds 2
Nucleus
Second shell holds 8
Third shell holds 8
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• As time went on and technology to explore the
  atom got better, we found other particles found
  in the atom.

Atomic Structure
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THE END