chemical spill in high school lab
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Chemical Spill in High School Lab January 26, 2006 - Five people needed hospital treatment after a chemical spill inside Middle Township High School in Cape May County. - PowerPoint PPT PresentationTRANSCRIPT
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• Chemical Spill in High School Lab
• January 26, 2006 - Five people needed hospital treatment after a chemical spill inside Middle Township High School in Cape May County.
• Police say it happened around 4 Thursday afternoon after school had been dismissed. Officials say some students in a lab classroom dropped a gallon of acetic acid. Hazardous materials crews were called in to clean it up.
• Five people were overcome by the fumes. They were treated and released from area hospitals. School will be open as usual Friday.
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Dmitri Mendeleev
• In 1869, came up with the idea to arrange the known elements in a table.
• Arranged them in order of increasing atomic mass.
• He left blanks where he knew as yet undiscovered elements should go.
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Henry Moseley
• In 1913, arranged the elements in order of increasing atomic number
• In 1869, Mendeleev did not know about protons yet.
• When arranged this way, there are patterns in their physical and chemical properties (The Periodic Law)
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Periodic Properties• Density
• Atomic radius (size)
• Electronegativity—ability of an atom to attract electrons in a bond
• Ions and charges within a group
• Ionization energy—energy required to remove an electron from an atom
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Valence Electrons• Valence e- --e- that exists at the highest
energy level of that element’s atoms– Outermost electrons– Only electrons involved in bonding– Group # = no. of valence e-
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Lewis Dot Diagrams• Shows the element symbol with valence electrons
as dots.
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Octet rule• An atom can achieve a full valence (octet) by
becoming an ion, but also by bonding with another atom. Bonding allows the two or more atoms to exchange or share atoms.
• Metals will lose electrons & form cations to gain an octet.
• Nonmetals will gain or share electrons to gain an octet.
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Bonding• There are two types of bonding:
• Ionic Covalent(molecular)– Metal to nonmetal Nonmetal to
nonmetal– Called a salt Called a
molecule– Electrons are handed over Electrons are shared– Opposite charges hold Can be single or
them together multiple bond
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Bonding in Metal Atoms
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Bonding• The difference in electronegativities of
the two atoms in the bond will determine what kind of bond it is:
–Ionic (>2.0) electrons handed over
–Polar covalent (0.4 – 2.0) unequal sharing of electrons
–Nonpolar covalent (<0.4) virtually equal sharing
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Octet Rule & Bonding
• Lewis Structures of molecules are diagrams that depict the electron arrangement in a molecule
• For instance: Chlorine (Cl2)
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Lewis Structures• Count the # of valence electrons each
atom in the molecule has.
• Total them.
• Distribute that many valence electrons among the molecule so that every atom has a full valence (8).
• Note: hydrogen only needs two.
• Multiple bonds may be necessary.
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Ionic vs Covalent Properties• Ionic Covalent
(molecular)
• Solids @ room temp. Could be any phase
• Very high melting pt. Low melting pt.
• Conduct elec. in H2O Do not conduct
• Form brittle crystals Form countless types of compounds
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Geometry
• VSEPR Theory—repulsion between electron pairs in a molecule cause them to shift so that they will be as far away from each other as possible.
• This repulsion causes molecules to have the shapes (geometry) that they have.
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Geometry
• Linear—two or more atoms in a straight line
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• Bent—bond angle is 104.5°
• Trigonal—atoms form a triangle in a single plane
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• Pyramidal-central atom surrounded by three atoms and an electron pair
• Tetrahedral-central atom surrounded by four atoms
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Polarity (Bonds)• A molecule can have a nonpolar covalent
bond.• A molecule can have a polar covalent bond. • This occurs when a highly electronegative
atom (O, F, Cl or N) is bonded to a less electronegative atom.
• In a polar bond, there is an uneven distribution of charge.
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Polarity (Molecules)• A molecule can also be polar or
nonpolar.
• Polarity of a molecule occurs when there is an uneven distribution of charge throughout the entire molecule. This is called a dipole.
• This can occur due to two factors: the bonds in the molecule, and the shape (geometry) of the molecule.
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Polarity (Molecules)• H2O
• C2H6
• CH4
• CH3F
• CO2
• A polar molecule will have drastically different properties than a nonpolar molecule.
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Polarity• Generally speaking:
– If it’s bent, it’s polar.– If it’s pyramidal, it’s polar.– If it’s linear w/2 identical atoms, it’s nonpolar.– If it’s linear w/O,N,F,CL and a diff’t atom, it’s
polar.– If it’s a tetrahedral w/4 identical atoms, it’s
nonpolar.– If it’s a tetrahedral w/3 identical atoms and
one atom of O,N,F or Cl, it’s polar.
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Erwin Schrödinger’s Model1926
• Mathematical equations describe the motion of electrons.