Monday, November 30th, 2009

Covalent-Network Compounds

• Some covalent compounds do not consist of individual molecules.
• Instead, Each atom is joined to all its neighbors in a covalently bonded, three-dimensional network
• The subscripts in a formula for a covalent-network compound indicate the smallest whole-number ratio of the atoms in the compound.

Ex: SiC-Silicon carbide

SiO2-Silicon dioxide

Si3N4-Trisilicon tetranitride

Acids and Salts

• Acid is a certain type of molecular compound.
• Most acids used in the laboratory can be classified as either binary acids or oxyacids.
• Binary Acids- Are acids that consist of two elements, usually hydrogen and one of the halogens-Fluorine, chlorine, bromine, iodine.
• Oxyacids- Are acids that contain hydrogen, oxygen and a third element (usually a nonmetal)
• In chemical nomenclature, the term acid usually refers to a solution in water of one of these special compounds rather than to the compound itself.
• For example, hydrochloric acid refers to a water solution of the molecular compound hydrogen chloride, HCl.
• Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids.

Ex. Sulfuric acid- H2SO4 Sulfate-SO2-/4

Nitric acid- HNO3 Nitrate-NO-/3

Phosphoric acid- H3PO4 Phosphate- PO3-/4

• An ionic compound composed of a cation and the anion from an acid is often referred to as a salt. Table salt, NaCl, contains the anion from hydrochloric acid. Calcium Sulfate, CaSO4, is a salt containing an anion from sulfuric acid. HCO-/3, Hydrogen carbonate ion bicarbonate ion.

Oxidation Numbers

• The charges on the ions composing an ionic compound reflect the electron distribution of the compound
• In order to indicate the general distribution of elections among the bonded atoms in a molecular compound or a polyatomic ion, oxidation numbers, also called oxidation states, are assigned to the atoms composing the compound or ion.
• Unlike ionic charges, oxidation numbers do not have an exact physical meaning.

Assigning Oxidation Numbers

• As a general rule in assigning oxidation numbers, shared electrons are assumed to belong to the more electronegative atom in each bond.
• More specific rules for determining oxidation numbers are provided by the following guidelines:

1. The atoms in a pure element have an oxidation number of zero. For example, the atoms in pure sodium, Na, oxygen, O2, phosphorus, P4, and sulfur, S8 all have oxidation numbers of zero.
2. The more-electronegative element in a binary molecular compound is assigned the number equal to the negative charge it would have as an anion. The less-electronegative atom is assigned the number equal to the positive charge it would have as a cation.
3. Fluorine has an oxidation number of -1 in all of its compounds because it is the most electronegative element.
4. Oxygen has an oxidation number of -2 in almost all compounds. Exceptions include when it is in peroxides, such as H2O2 , in which its oxidation number is -1, and when it is in compounds with fluorine, such as OF2, in which its oxidation number is +2.
5. Hydrogen has an oxidation number of +1 in all compounds containing elements that are more electronegative than it; it has an oxidation number of -1 in compounds with metals.
6. The algebraic sum of the oxidation numbers of all atoms in a neutral compound is equal to zero.
7. The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.
8. Although rules 1 through 7 apply to covalently bonded atoms, oxidation numbers can also be assigned to atoms in ionic compounds.

11/24/09

Hw assignment Monday night- fill out the bingo cards Dr. B is giving us, fill it in with the ions of charts 1 and 2 from chapter 7. We play bingo on Tuesday- winners get candy!!!!

Naming Binary Ionic Compounds

The Stock System of Nomenclature

• Some elements such as iron, form two or more cations with different charges
• To distinguish the ions formed by such elements, scientists use the stock system of nomenclature.
• The system uses a Roman numeral to indicate an ion's charge.

Compounds Containing Polyatomic Ions

• Many common polyatomic ions are oxyanions polyatomic ions that contain oxygen.
• Some elements can combine with oxygen to form more that one type of oxyanion
• Ex: nitrogen can form WO-3 or NO-2
• The name of the ion with the greater number of oxygen atoms end in -ate. The name of the ion with the smaller number of oxygen atons ends in -ite.

NO-3 NO-2

nitrate nitrite

• Some elements can form more than two types of oxyanions.
• Ex: Chlorine can form ClO-, ClO-2, ClO-3, ClO-4
• In this case, an anion that has one fewer oxygen atom than the -ite anion has is given the prefix -hypo.
• An anion that has one more oxygen atom thatn the -ate anion has is given the prefix per-.

ClO- ClO-2 Cl0-3 ClO-4

hypochlorite chlorite chlorate perchlorate

DO NOT SAY DIMERCURY, CALL IT MERCURY 1 OR 2.

Naming Compounds with Polyatomic Ions

• Name the cation
• Name the anion
• Name the salt- names of cation and anion

YOU WANT POLYATOMIC IONIC COMPOUNDS TO BE ELECTRICALLY NEUTRAL

YOU CANNOT MOVE ATOMS FROM 1 POLYATOMIC ION TO THE NEXT

Naming Binary Molecular Compounds

• Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules.
• As with ionic compounds, there is also a stock system for naming molecular compounds.
• The old system of naming molecular compounds is based on the use of prefixes.
• Ex: CCl4- carbon tetrachloride (tetra=4)
• Ex: CO-carbon monoxide( mon=1)
• Ex: CO2- carbon dioxide ( di=2)

Covalent -Network Compounds

• Same covalent............ (TO BE CONTINUED!!)

Movie

So I know Dr. B wasn't at school today, but this movie really interested me. I think it's cool how Orpheus crashed into the Earth back in the day. I never realized that the way planets collide cause such different outcomes. Where do you think is the next place humans will travel after Mars? Will we ever find another easily inhabitable planet? Anyone else have something to add?

11/22/09

Hey guys, sorry it took so long to get the blog up.

CH 7.
Significance of a Chemical Formula.

• a chemical formula indicates the relative numbers of each kind of atoms in a chemical compound.
• for a molecular compound, the chemical formula reveals the number of each element conrained in a single molecule of a compound.
• ex. octane - C8H18 (subscripts after element symbols express number of each atom in the molecule.
• the chemical formula for an ionic compound represents one formula unit - the simplest ratio of the compounds positive ions (cations) and its negative ions (anions.)
• ex. Al2(SO4)3
• ( ) around the polyatomic ion identifies it as the unit.
• note. no subscript = UNDERSTOOD TO BE 1.
• Monatomic Ions
• many main-group elements can gain or lose e- to form ions.
• ions formed from a single atom are known as monatomic ions.
• some main-group elements tend to form covalent bonds eather than form ions.
• Naming Monatomic Ions
• monatomic cations are identified simply by elements' name.
• ex. K+ is called potassium cation.
• Mg 2+ is called magnesium cation.
• for monatomic anions, ending of elements' name is dropped, and the ending "-ide" is added to the root name.
• ex. F- is called FLOURIDE anion.
• N3- is called the NITRIDE anion.
• STUDY THE CHAPTER 7 CHARTS GUYS.
• Binary Ionic Compounds
• compunds composed of 2 elements are known as binary compounds.
• in a binary ionic compound, the total number of positive charges and negative charges must be equal.
• the formula for a binary ionic compound can be written given the identities of the compound's ion.
• ex. magnesium bromide
• ions: Mg2+, Br-, Br-
• = MgBr2
• Al3+O2-
• Al2O3
• "CROSS OVER METHOD" = bleh.
• Naming Binary Ionic Compounds
• the nomenclature, or naming system, of binary ionic compounds involves combining the names of the compound's positive and negative ions.
• the name of the cation is given 1st; followed by name of the anion.
• ex. Al2O3 - aluminum oxide.

Post/Comment Tally

I have counted your posts for the quarter and I will let you know today as you turn in your test what your current count is. There are 15 days left in this quarter. That does NOT include today since we are having a test. Every other day after today is counted. To date, 2 people have posted or commented 20 or more times. 5 of you are in single digits. Everyone has at least one comment/post. One person can not get 20 by the end of the quarter and one person will have to comment every SINGLE day to get to 20. Comments on this post will NOT count for your total!

Direction of Dipoles is represented by an arrow toward negative poles and a cross at the positive pole. the positive dipole is indicated as follows

-I-->

H Cl

the negative region in one polar molecule attracts the positive region in adjacent molecules. the moleules are attracted to each other by opposite sides.

each forces of attraction between polar moleules are known as a dipole- dipole forces

dipole-dipole foreces act at short range only between nearyby molecules.

this explains the high boiling point in molcules with dipole dipole forcesex I-Cl (97 c) but Br-Br (59 c)

a polar molecule can induce a dipole in a non polar molecule by temporarily attracting its electrons

the result is a short range intermolecular force that is weaker than a dipole-dipole force.

this accounts for the oxygen's ability to be dissolved into water

some hydrogen containg compounds have high boiling points. explored by a particularly strong of dipole-dipole force

examples are phosphorous and sulfur

this gives a hydrogen atom a positive charge that is almost half that of a bare proton

the small size of the hydrogen atom allows it come close to an unshared pair in another atom

this forms a hydrogen bond

these are connected with a dotted line

excellent example is water

properties aquired from hydrogen bonding are surface tension, cohesion, solvent, and boiling point is raised

london dispersion theory

even noble gas atoms and non polar molecules can experience weak intermolceular bonding

in any atom or molecule the electrons are in constant motion

thus there exists a possibilty of there being a more positive and negative side which attracts the more negative or positive sides of a different atom or molecule

this is the weakest type of bond

suggested in 1930

11/17/09

HYBRIDIZATION(HB): the blending of bonding orbitals

• 2 types of bonding: Sigma(o-) and Pi(~)(I know these aren't the actual signs but i do not know how to make them on a computer so I will just use these)
• Sigma is ALWAYS the first bond
• Pi will be the second bond or any after that
• Single bond: 1 o-
• Double bond: 1 o-, 1 ~
• Triple bond: 1 o-, 2~

IN HYBRIDIZATION YOU ONLY PAY ATTENTION TO THE SIGMA BONDS AND LONE PAIRS(LP)!!!!!!!!!!

• Example: Methane, CH4

(Hydrogen does not form hybrids)

Because HB is o- bonds plus LPs, to hybrid Carbon, first find out the number of o- bonds, ~ bonds and LPs. (You may have to draw the Lewis structure for this). In C there are 4 o- bonds and no LPs. Therefore the HB=4=sp^3.

• If HB results in an sp orbital, then the molecular geometry is 180 degrees(linear)
• If HB results in an sp^2 orbital, then the molecular geometry is 120 degrees(trigonal-planar)
• If HB results in an sp^3 orbital, then the molecular geometry is 109.5 degrees(tetrahedral)

Intermolecular Forces (IMF)

• The forces of attraction between molecules are known as intermolecular forces
• The boiling point of a liquid is a good measure of the IMF but its molecules: the higher the boiling point, the stronger the forces between the molecules
• IMF varies in strength but are generally weaker between atoms within molecules, ions in ionic compounds, or metal atoms in solid metals
• Boiling points for ionic compoundsand metals to be much higher than those for molecular substances: forces between molecules are weaker than those between metal atoms or ions
• The strongest IMF is between polar molecules
• Because of their uneven charge distribution, polar molecules have dipoles. A dipole is created by equal but opposite charges that are separated by a short distance
• The direction of a dipole is from the dipole's positive pole to it's negative pole

TEST IS THURSDAY! MAKE SURE YOU STUDY! READ THE CHAPTER

HOMEWORK: PAGE 211-212, #'s 50-60. IT IS HOMEWORK 6

(If you couldn't tell, I decided to go Memphis colors for the game tonight because Memphis is the best team in the nation. Hope you can read the gray good enough. I don't think it should be a problem. GO TIGERS!!!!)

PS Ben Smith

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