Fundamentals of chemistry

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< Wikiversity:School of Chemistry

The fundamentals of Chemistry is an introduction to the Periodic Table, stoichiometry, chemical states, equilibria, acid/bases, oxidation/reduction reaction, kinetics, bonding, among other parts of chemistry.

Contents 1 Periodic Table of Elements 2 Stoichiometry 3 Chemical States 4 pH 4.1 Acids 4.2 Bases 5 References 6 See also

[edit] Periodic Table of Elements

Each chemical element in the universe has unique properties which distinguish it from all of the other chemical elements. Though each is unique, the elements can be still grouped by their commonalities in a useful and meaningful way. The periodic table groups the elements by properties. For the History of the Periodic Table, check out Early Chemistry or Wikipedia's History of the Periodic Table.

The Periodic Table is available here: Periodic Table on Wikipedia and explanations will be based on this table. A good idea is to have a printed hard copy of the periodic table.

Each element has their own box and these boxes make up groups and rows. There are eighteen groups (or families or columns) on the periodic table. Each one represents how many electrons are attached to the elements and correlate to how many valence electrons are present. Electrons are negatively charged subatomic particles that revolve around the nucleus of the element. Valence electrons are electrons that are on the very outside of the atom. There are seven periods (or horizontal rows) that describe electron shells, but more details on electron shells will be discussed in advanced pages.

Traditionally the boxes have certain informative parts about the element. Let's look at hydrogen's box. The "1" in the top corner is the atomic number, which deals with how many protons, or positive charges, are in the atom. The "H" is the symbol for Hydrogen. All the elements get a one or two letter symbol (there are a couple of exceptions with undeclared elements). The number at the bottom is the atomic weight or atomic mass. 1.00794 represents how many grams are in each mole (6.022×10²³ entities) of hydrogen. The atomic mass is a very important part of chemistry and has many applications throughout.

There are eight distinct groups that need to be discussed. The first two groups (1A and 2A) as well as the six on the very right (3A-8A). These are called representative elements. Group 1A are alkali metals (except Hydrogen which is a non-metal) and Group 2A are alkaline earth metals. Group 3A through 8A are mixed in properties, but there are specific trends.

[edit] Stoichiometry

Stoichiometry is used to calculate quantitative measurements within chemical reactions. In order for stoichiometric relationships to work, one must consider the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. One must remember that mass or matter is neither created nor destroyed.

Here is an example of how one stoichiometry is used to balance equations. Acetylene is added to oxygen gas to create carbon dioxide and water. This reaction could be written as follows.

Unbalanced equation

However, the above equation is not balanced.

• On the left side there are two Carbon atoms (C), two Hydrogen atoms (H) and two Oxygen atoms.
• On the right there is one Carbon atom, three Oxygen atoms, and two Hydrogen atoms.

It would not be correct to balance it by changing the subscript numbers.

Incorrectly balanced equation

By changing the subscripts we indicate a different reaction. The above are impossibilities that will be discussed later on pages about Lewis structure and electron configuration.

In order to balance the equation correctly, a number must be added to the front of each molecule. These numbers are called coefficients.

Correctly balanced equation

As one can see, the subscripts were not touched, only whole numbers were added to the front of all the molecules, as needed. One can include fractions, yet for clarity and simplicity whole numbers are generally used.

The (g) and (l) represent the compound chemical state; the "l" stands for liquid, the "g" stands for gas, an "s" would stand for solid, and an "aq" would stand for aqueous. Plasma can also exist, which is an ionized gas with special properties.

[edit] Chemical States

There are four states of matter, plasma being the most common in the known universe. The other three are gas, liquid and solid, from least to most dense. A fifth, the Bose-Einstein condensate, can only exist in temperatures approaching absolute zero. It has limited applications in chemistry.

Gases are made up of atoms and/or molecules that are freely moving and therefore have not definite shape. They morph uniformly to the shape of the container that they are in. If the container is not sealed, then the gas can move out. Therefore the volume of the gas is reliant on the temperature and/or pressure throughout the gas or environment. This is observed using the ideal gas laws, which are discussed later.

An important piece of information to know is what an aqueous solution is also. Aqueous solutions are not technically chemical states, but they appear often enough when dealing with stoichiometry and chemistry in general that they should be mentioned.

[edit] pH

The potential of hydrogen or pH (pronounced /piː.eitʃ/) is a measure of the acidity or alkalinity of a solution, numerically equal to 7 for neutral solutions, increasing pH with rising alkalinity and decreasing pH with more acidity. The pH scale commonly in use ranges from 0 to 14.

An alkali is sometimes called a "base".

Representative pH values

Substance	pH
Battery acid	0.5
Gastric acid	1.5 – 2.0
Lemon juice	2.4
Cola	2.5
Vinegar	2.9
Orange or apple juice	3.5
Beer	4.5
Acid Rain	<5.0
Coffee	5.0
Tea or healthy skin	5.5
Milk	6.5
Pure water	7.0
Healthy human saliva	6.5 – 7.4
Blood	7.34 – 7.45
Sea water	8.0
Hand soap	9.0 – 10.0
Household ammonia	11.5
Bleach	12.5
Household lye	13.5

Mathematically, calculate pH using the following equation:

pH = − log[H ⁺ ]

Mathematically, calculate pOH using the following equation:

pOH = − log[OH ⁻ ]

Combining (adding) the results of pH with pOH should equal fourteen (14).

pH + pOH = 14

[edit] Acids

Characteristics of acids:

• Aqueous acids can turn blue litmus towards red.
• React with bases and certain metals to form salts.
• Arrhenius definition of acid: Yields hydrogen ions when dissolved in water.
• The Lewis definition of an acid: Can accept a pair of electrons to form a covalent bond.
• Brønsted-Lowry acid definition: A species that can lose or "donate" a hydrogen ion
• Can have a sour taste.
• Can give one or more than one protons (or simply, H⁺)
• Electrolytes, yet usually are not ionic compounds

[edit] Bases

Characteristics of bases:

• Aqueous bases (alkalis) can turn red litmus towards blue.
• React with acids to form salts.
• Arrehenius definition of base: produce OH⁻ ions when dissolved in water.
• Lewis definition of Base: can donate a pair of electrons to form a covalent bond with an acid
• Brønsted-Lowry base definition: A species that can gain or "accept" a hydrogen ion
• Can have a bitter taste.
• Can accept one or more than one protons (or simpler H⁺)
• Conduct electricity

The difference between bases and alkalis is that alkalis dissolve in water and are considered basic salts of alkaline metals. An example of a base that is not an alkali is ammonia (NH₃).

[edit] References

Properties of alkalies and acids

[edit] See also

• Acids and Bases
• The School of Chemistry