• 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.

Bonding and Geometry

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.

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)

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

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-

Lewis Dot Diagrams• Shows the element symbol with valence electrons

as dots.

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.

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

Bonding in Metal Atoms

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

Octet Rule & Bonding

• Lewis Structures of molecules are diagrams that depict the electron arrangement in a molecule

• For instance: Chlorine (Cl2)

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.

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

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.

Geometry

• Linear—two or more atoms in a straight line

• Bent—bond angle is 104.5°

• Trigonal—atoms form a triangle in a single plane

• Pyramidal-central atom surrounded by three atoms and an electron pair

• Tetrahedral-central atom surrounded by four atoms

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.

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.

Polarity (Molecules)• H2O

• C2H6

• CH4

• CH3F

• CO2

• A polar molecule will have drastically different properties than a nonpolar molecule.

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.

Erwin Schrödinger’s Model1926

• Mathematical equations describe the motion of electrons.