SECTIONS

General Stuff/Energy and Matter

Atomic Structure

Electron Configuration & The Periodic Table

Chem Formulas and Bonding & Molecular Shape

Chemical Reactions and Equations, heat, and Gas laws

Section 6: Chemical Formulas and Bonding
Go here:
http://www.geocities.com/chembonding2000/pages/index.htm

Ionic Bonds-
Ionic bond- a positively charged ion is attracted to a negatively charged ion; these commonly form between metal and nonmetal ions
Ionic compound- a compound composed entirely of ions
-Cations- positively charged ions found in a compound
-Anions- negatively charged ions found in a compound
-To maximize electrical attraction among them, elements alternate

Octet Rule-
-nonmetal+metal = more stable material
-octet rule: atoms tend to lose, gain, or share electrons in order to acquire the full set of valence electrons
-Excludes transition and inner transition

Lewis Dot Diagram
-Scientists consider valence electrons when determining chemical bonding
-Lewis dot diagrams – simple way to display it

Types of Ions--
-Monatomic ions- one-atom ions
-Polymonic ions- made from group of more than one ion
-Monatomic cations- have same name as element
Elements in group 1 each form monatomic cations of charge of 1+, group 2 +, and so on
To distinguish different cations of a transition metal, chemists add Roman numerals to the element name – for example, iron(III)
-Monatomic Anions-
Nonmetals form anions most easily (with 1- charge)
Says –ide at end
-Polynomic Ions
Ions consisting of more than one atom

As a unit, forms an ionic bond with an ion of the opposite charge
Binary ionic compounds- contain the ions of only two elements
-Write name of cation followed by name of anion
-Empirical formula- called the chemical formula- uses symbols to indicate the atoms or ions in a compound, with subscripts added to indicate ratios
-The reason that ratios are not 1:1 is that all ionic compounds are electrically neutral
-Crisscross- crisscross charges without charge to produce ion
Sometimes needs to be simplified
When you write formulas for polyatomic atoms, put parenthesis around them

Covalent Bonds-
Covalent bond- formed by a shared pair of electrons between two atoms (group of atoms united by them is called “molecule”)
-structured formula indicates what bonds to what
Unshared pair- when a pair is not shared in a bond
Double bond- 2 bonds
Triple bond- 3 bonds
Coordinate covalent bond- an electron is “given”
Polar covalent- one atom is more electronegative than the other
Nonpolar covalent- both atoms exert approximately equal pull

Section 7: Molecular Shape

The Shape of Small Molecules-
Similar electrical charges cause valence electron pairs to repel each other, leading to the valence- shell electron pair repulsion theory (VSEPR): in a small molecule the pairs of valence electrons are arranged as far apart from each other as possible

Shapes:
-Pyramidal: An unshared pair of valence electrons not involved in the bond (which exerts a greater repulsion force- they take up more room around an atom- because they are held by 1 atom’s nucleus only) causing the bond angle to be slightly less than that of a tetrahedral molecule
-Bent: example: H20 has 2 pairs of unshared valence electrons, which exert greater amounts of repulsion force than do the two bonding pairs. As a result, the two H atoms in the water molecule are separated by a slightly smaller angle than they would be in a tetrahedral of a pyramidal molecule.

Hybrid Orbitals:
When an atom approaches another atom to bond, the orbitals of its electrons may be changed. The atomic orbitals mix together forming hybrid orbitals. An atom’s h orbitals have a combo of the proerties of the atomic orbitals that formed them.
In a linear molecule the 2 orbitals around the central atom form from mixing an “s” orbital and a “p” orbital (called sp orbitals)
When an atom has 4 pairs of valence electrons around it, and none of these is in a multiple bond, 4 hybrid orbitals form from mixing an s orbital and three p orbitals (sp3 is what its called)

Bond Length-
In real molecules, different pairs of atoms form bonds of different lengths. As you move down a group of the periodic table, the atoms form longer bonds. Multiple bonds are shorter than single bonds. Two nuclei repel each other because they are both positively charged. But a bond is made of electrons, which are negative. The more electrons in a bond, the stronger the bond attracts the positively charged nuclei of the bonding atoms.

Polarity-
A molecule can be polar or nonpolar.
Polar- has one end with a positive charge and the other end with a negative charge. These are known as dipoles, as they have different charged ends.
Being polar or nonpolar gives a molecule a variety of different properties. A collection of polar molecules will align in an electrical field, whereas nonpolar molecules will not. Polar molecules will be attracted to a charged rod or be deflected by a magnetic field. You can distinguish between the two using the shape of the molecule and the polarity of the bonds.
Nonpolar- a bond with only nonpolar bonds, and no polar bonds

Large Molecules-
The polarity of a large molecule helps determine its shape (proteins).
A protein is composed of subunits connected in chains. These cause it to bend and kink. For a protein, molecular attractions tend to group the nonpolar subunits on the inside and polar subunits on the outside, thus giving a protein a a complex, 3-d shape. These shapes allow proteins to serve a variety of specialized functions.