Atoms, Elements, and The Periodic Table

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Atoms, Elements, and The Periodic Table
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Atoms

• Smallest particles of matter
• Have all the characteristics of the element
• The nucleus is the central part of the atom
• contains two types of subatomic particles
• proton positively charged the number of
  protons is the atomic number mass 1amu
• neutron no electromagnetic charge mass 1 amu
• Electrons
• negatively charged particles
• negligible mass
• move around the nucleus at the speed of light.
• Atoms have the same number of protons and
  electrons.

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Elements

• Made of one type of atom.
• Pure substances
• Simplest form of matter
• Unique properties determined by the number of
  neutrons, protons, and electrons.
• There are 114 known elements
• 93 naturally occurring
• 21 synthetic
• Atomic weight of an element
• is the average of the atomic masses of all the
  stable and radioactive isotopes of an element

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• Isotope of an element
• Isotopes are atoms of an element
• same atomic number (same number of protons)
• Different number of neutrons
• Can be stable or unstable
• Unstable isotopes are radioactive and decay to
  form atoms of other elements
• examples
• U-238 decays to Pb-206 (half-life 4.5 Billion
  years)
• U-235 decays to Pb-208 (half-life 704 Million
  years)
• C-14 decays to N-14 (half-life 5730 years)
• any isotope which has an atomic number greater
  than that for bismuth (Bi) is unstable

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Periodic Table

• Shows all of the elements
• Elements are arranged by atomic number (number of
  protons, from light to heavy.)
• Rows are from left to right
• Columns
• grouped by similar characteristics
• known as Groups or Families
• Left side of table metals
• Right side of table nonmetals
• Middle metalloids

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The Periodic Table
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Group 1A Alkali Metals

• Very reactive
• All are metals except H
• Easily give up their one valence electron to
  combine with nonmetals from group 7A Ex. NaCl

Cutting sodium metal
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Opposites Attract
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Valence Electrons

• Electrons are located in regions called energy
  levels.
• Each energy level contains a certain amount of
  electrons
• Valence electrons are the electrons in the outer
  shell of an atom.
• The amount of electrons in the outer layer
  explains how atoms form compounds.

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Group 2A Alkaline Earth Metals

• All are metals
• React with oxygen and water
• Have 2 valence electrons so they are not as
  reactive as Alkali Metals
• Ex. MgO, MgS

Magnesium
MgO
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Transition Elements

• Most are hard and have high melting points
• These are all metals
• Give up valence electrons
• Have variable numbers of electrons
• Many form compounds of main ore minerals. Ex. Cu,
  Fe, Mo, W

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• Group 3A Metalloids, Includes Aluminum
• 4 valence electrons
• Group 4A aka Carbon Groups
• Includes metals and nonmetals.
• Elements have lower melting and boiling points.
• 5 valence electrons
• Group 5A Nitrogen Group have 6 valence electrons
• Group 6A Oxygen Family have 7 valence electrons

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Group 7A The Halogens (salt makers) F, Cl, Br,
I, At

• Found in pairs, highly reactive
• Have 7 valence electrons
• React with alkali metals to form salts

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Group 8A The Noble (Inert) GasesHe, Ne, Ar, Kr,
Xe, Rn

• Wont react because they have full electron
  levels (8 valence electrons
• All elements are gases