General Chemistry Topics

General Chemistry Topics

Robert H. Helvey

Periodic Table of The Elements

Stoichiometry: The Meaning of the Word

The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning "measure").
Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in chemical reaction.

A. How to Carry out mole-to-mole calculations for a chemical reaction

Step1. Write the balanced chemical equation for the reaction of interest.

Step 2. Find the stoichiometric relation between the two substances of interest and use it to write the mole to mole ratio in the form

Substance required/Substance given

Step 3. Apply this conversion factor to the information given and obtain the information required.

Comprehensive web page related to different aspects of stoichiometry:

Redox

Table 1. Rules for Assigning an Oxidation Number (O.N.)

General Rules
1. For an atom in its elemental form (Na, O, Cl, and so forth: O.N.=0 2. For a monatomic ion: O.N.= ion charge 3. The sum of O.N. values for the atoms in a compound equals zero. The sum of O.N. values for the atoms in a polyatomic ion equals the ion charge.
Rules for specific atoms or periodic table groups
1. For Group 1A (1)	O.N. = +1 in all compounds
2. For Group 2A(2)	O.N.= +2 in all compounds
3. For Hydrogen	O.N.= +1 in combination with nonmetals O.N.= -1 in combination with metals and boron
4. For fluorine	O.N.= -1 in all compounds
5. For Oxygen	O.N. = -1 in peroxides O.N.= -2 in all other compounds (except with F)
6 For Group 7A (17)	O.N.= -1 in combination with metals, nonmetals (except O), and other halogens lower in the group

Example 1.

Give the oxidation number of carbon in each of the following: (a) CF₂Cl₂; (b) Na₂C₂O₄

A. CF₂Cl₂. Each F and each Cl has an O.N. of -1; two F and two Cl gives -4. Therefore, the O.N. of C is +4.

B. Na₂C₂O₄. Each Na has an O.N. of +1; two Na gives +2. Each O has an O.N. of -2; for O gives -8. Therefore, the total of the O.N.s of the two C atoms is +6 and each C is +3.

Web pages pertaining redox reactions.

Gases

Fundamental principles related to the chemistry of gases.

If you warm a container, wouldn't you expect the particles to move faster? According to the Kinetic Theory, the particles will have more energy and hit each other and the sides of the container more often, forcing the walls to move outward and increasing the volume. Therefore, volume and temperature are directly proportional which is called Charles' Law. but remember, you cannot change the amount of gas or the pressure!

V₁ / T₁ = V₂/ T₂ ; constant n and P

Well, now allow the pressure to change but lock the wall in place. Increasing the temperature will also increase the pressure of the container, if the volume is not allowed to change.

P₁ / T₁ = P₂/ T₂; constant n and V

The three laws discussed can be brought together to create a combined gas law. Now that the combined gas law is stated, it isn't really necessary to memorize the equations for other laws. Each gas law can be derived from this new combined equation. This equation is useful when you want to change some of the conditions in the container and want to know how the changes will affect the other variables. For instance if we know an original volume, temperature, and pressure of a container, we can calculate what the new temperature should be if the pressure and volume are changed.

P₁ x V₁/ T₁ = P₂ x V₂/ T₂

Web pages related to the chemistry of gases.

Bonding

Table 2. Chemical bond arrangements

Number of electron pairs	Arrangement of electron pairs	Molecular geometry	Examples
2	Linear, bond angle 180⁰	Linear	BeCl₂, HgCl₂
3	Trigonal planar, bond angle 120⁰	Trigonal planar	BF₃
4	Tetrahedral, bond angle 109.5⁰	Tetrahedral	CH_4,NH₄⁺
5	Trigonal bipyramidal, bond angle 90⁰,and 120⁰	Trigonal bipyramidal	PCl₅
6	Octahedral, bond angle of 90⁰	Octahedral	SF₆

Example 2. Hydrogen bonding between water molecules

Example 3. Ionic Bonding between salt crysticals (NaCl)

Covalent Bonding is where to atom share electron in their outer shell to complete their octet of that of a noble gas formation.

Example 4.Polar Bonds (NH₄) Methane

Methane, which has four equal hydrogen bonds. Because the symmetrical distribution of the polar bonds in the molecule cancels out the effects of the bond polarity, methane remains neutral. If we were to replace one hydrogen with a chlorine atom (forming chloromethane), the chlorine atom would attract the shared pair of electrons more strongly than the hydrogen opposite to it. Thus, the molecule becomes slightly polar.

The Octet Rule
The valence shell of the noble gases other than helium all contain eight electrons, and the tendency of many atoms to acquire such an outer shell electron configuration forms the basis of the octet rule.

Octet Rule: When atoms react, they tend to achieve an outer shell having eight electrons.

Many of the representative elements (sodium and chlorine for instance) follow this rule when they form ions. In the ionic case they achieve the noble gas shell configuration by either a gain or loss of electrons. When atoms other than hydrogen form covalent bonds, an octet is accomplished by sharing. The octet rule can be used to explain the number of covalent bonds an atom forms. This number normally equals the number of electrons that atom needs to have a total of eight electrons (an octet) in its outer shell. For example, the halogens (Group VIIA), all have seven valence electrons.

Web pages pertaining to chemical bonding.

Sources: Location In Morehead State Library

Main Author:
Iff, James B., 1935-
Title:
General chemistry; readings from Scientific American. With introductions by James B. Ifft
[and] John E. Hearst.
Publication Information:
San Francisco, W. H. Freeman [c1974]
Description:
434 p. illus. 29 cm.

Subject's):
Chemistry.

Location:
MAIN COLLECTION
Call Number:
540 I23G

Main Author:
Hirschfelder, Joseph Oakland, 1911-
Title:
Molecular theory of gases and liquids [by] Joseph O. Hirschfelder, Charles F. Curtiss [and] R.
Byron Bird, with the assistance of the staff of the University of Wisconsin Naval Research
Laboratory.
Publication Information:
New York, Wiley [1954]
Description:
1219 p. illus. 24 cm.

Subject's):
Molecular theory.
Gases.
Liquids.

Location:
MAIN COLLECTION
Call Number:
539.1 H669M

Title:
Ion-molecule reactions in the gas phase; a symposium.
Publication Information:
Washington, American Chemical Society, 1966.
Description:
viii, 336 p. illus. 24 cm.

Subject(s):
Mass spectrometry.
Ions.
Molecules.
Gases.

Location:
MAIN COLLECTION
Call Number:
545.33 I64

Title:
Advances in electron transfer chemistry.
Publication Information:
Greenwich, Conn. : JAI Press, c1991-
Description:
v. : ill. ; 24 cm.
Annual

Subject(s):
Oxidation-reduction reaction--Periodicals.
Charge transfer--Periodicals.

Location:
MAIN COLLECTION
Call Number:
541.393 A244

Main Author:
Clark, W. Mansfield (William Mansfield), 1884-1964.
Title:
Oxidation-reduction potentials of organic systems / by W. Mansfield Clark.
Publication Information:
Huntington, N.Y. Robert E. Krieger Publishing Company 1972,c1960.
Description:
xi, 584 [3] p. : ill. ; 24 cm.

Subject(s):
Oxidation-reduction reaction.
Chemistry, Organic.

Location:
MAIN COLLECTION
Call Number:
547.23 C596O

Main Author:
Reynolds, Warren L. (Warren Lind)
Title:
Mechanisms of electron transfer [by] Warren L. Reynolds and Rufus W. Lumry.
Publication Information:
New York, Ronald Press Co. [1966]
Description:
vi, 175 p. 24 cm.

Subject(s):
Oxidation-reduction reaction.

Location:
MAIN COLLECTION
Call Number:
546.123 R466M

Publication Information:
Cleveland, Ohio : CRC Press, c1977-
Description:
v. : ill. ; 26 cm.
Annual

Subject(s):
Chemistry--Tables.
Physics--Tables.

Location:
MAIN COLLECTION
Call Number:
541.9 H236 1991-92

Location:
MAIN COLLECTION
Call Number:
541.9 H236 1991-92

Location:
MAIN COLLECTION
Call Number:
541.9 H236 1995-96

Location:
REFERENCE COLLECTION (Noncirculating)
Call Number:
541.9 H236 1991-9

Location:
REFERENCE COLLECTION (Noncirculating)
Call Number:
541.9 H236 1997-98