The Periodic Table

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The Periodic Table
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The Periodic Table

• Elements are represented by symbols.
• Arranged in order based on the number of protons
  an atom of that element has in the nucleus.
• Periodic Law states when elements are arranged
  this way, similarities in their properties will
  occur in regular pattern.

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History of the Periodic Table

• Russian scientist Dmitri Mendeleev
• Mid 1800s - About 70 elements were known.
• Wrote down the elements in order of increasing
  mass.
• Found a pattern of repeating properties.

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Mendeleevs Table

• Grouped elements in columns by similar properties
  in order of increasing atomic mass.
• Found some inconsistencies - felt that the
  properties were more important than the mass, so
  switched order.
• Found some gaps.
• Must be undiscovered elements.
• Predicted their properties before
• they were found.

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The Modern Periodic Table

• Elements are still grouped by properties.
• Similar properties are in the same column.
• Order is in increasing atomic number (first
  scientist to do this was Moseley).
• Added a column of elements Mendeleev didnt know
  about.
• The noble gases had not been found
• because they didnt react with
• anything.

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Atomic Number

• The number of protons in the nucleus of an atom.

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Symbols Atomic Number
A
Y
23
X
Na
Z
11
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Mass Number

• The sum of the numbers of protons and neutrons in
  the nucleus of an atom.

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Symbols Mass Number
A
Y
23
X
Na
Z
11
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The Mass of an Atom

• Atomic mass unit (amu) describes the mass of an
  atom or molecule it is exactly 1/12th the mass
  of a carbon atom. Used because the masses of
  atoms are very tiny, so the numbers would be too
  small to work with.
• Average atomic mass weighted average that
  includes common isotopes.

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Calculating the Number of Neutrons

• Subtract the mass number from the atomic number.

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X
A
Na
Y
23
11
Z
Neutrons A Z Example Na 23-1112
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Ions

• An atom, or group of atoms, that has lost or
  gained one or more electrons and has a negative
  or positive charge.
• Cation ion with a positive charge.
• Anion ion with a negative charge.

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X
A
Na
Y
1
23
11
Z
Electrons Z - Y Example Na 11 1 10
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Distinguishing Between Atoms

• Definition ISOTOPE- Atoms of same element with
  different numbers of neutrons
• Isotopes have similar chemical
• properties because the proton
• an electron counts are the same.
• However Isotopes may have different physical
  properties such as density

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Naming Isotopes

• Put the mass number after the name of the element
• carbon- 12
• carbon -14
• uranium-235

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Isotopes of Hydrogen
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Hydrogen makes up less than 1 of the Earths
crust. Only 1 out of every 6000 hydrogen atoms is
deuterium
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Seventy-five percent of the mass of the sun is
hydrogen, with protium isotopes outnumbering
deuterium 50,000 to 1.
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PRACTICE TIME!!!!
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Families of Elements

• Elements are classified into three groups
• Metals
• Nonmetals
• Semiconductors (metalloids)

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• The elements in the A groups are called the
  representative elements

8A
1A
2A
3A
4A
5A
6A
7A
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• You must also tell the difference between metals,
  non-metals and metalloids (semi-conductors).

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Metals

• An element that is shiny and conducts heat and
  electricity well.

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• Every thing below and to the left of the steps,
  (In yellow) are metals.

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Alkali Metals

• Soft, shiny, and react violently with water.

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Alkaline-Earth Metals

• Found in limestone and the human body.
• Less reactive that alkali metals, but can still
  react to form positive ions with a 2 charge.
• Examples calcium, magnesium

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• Group 1A are the alkali metals
• Group 2A are the alkaline earth metals

1A
2A
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Transition Metals

• Much less reactive, but can form positive ions.

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• The group B are called the transition elements

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• Top row of the inner transition is called the
  Lanthanide series.
• Bottom row called the
• Actinide series.

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Synthetic Elements

• Man-made elements
• All elements with atomic number greater than 92
  are synthetic.
• All radioactive

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Nonmetals

• An element that conducts heat and electricity
  poorly.
• Most plentiful on earth.

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• Every thing above and to the right of the steps,
  (In purple) are non-metals.

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• Hydrogen (in white) is usually considered to be a
  non metal, but due to its reactivity it has its
  own group.

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Semiconductors

• Metalloids
• An element of compound that conducts electric
  current better than an insulator, but not as well
  as a conductor does.
• Only 6 boron, silicon, germanium, arsenic,
  antimony, and tellurium.

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• They form steps from Boron to Tellurium
• with Germanium and
• Antimony (Green) and separate the metals
  from non-metals.

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Halogens

• Group 17
• Highly reactive!!!

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Noble Gases

• Group 18
• Exist as single atoms.
• Un-reactive.
• Do not form ions!!

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• Group 7A is called the Halogens
• Group 8A are the noble gases

8A
7A
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Periods and Groups

• Periods tells the number of electrons and their
  arrangement in the orbitals, horizontal rows.
• Groups Tells the number of valence electrons
  vertical rows.
• We will come back to this later.