By the end of this lesson, you should be able to:

2. Properly use atomic number, mass, name, and symbol.

3. Use the periodic table of elements, discuss its layout, and identify at least one group of elements.

4. Distinguish metals, nonmetals, and metalloids by name using a periodic table of elements.

5. Describe the following types of chemical bonding: covalent, ionic, metallic, secondary.

6. Chemically distinguish acids from bases, and describe the pH scale.

7. Define "polymer."

Atoms and Elements

An atom is the smallest unit of an element that retains the properties of that element. Atoms are composed of different subatomic particles. Most notably, the center or nucleus of the atom contains protons (with a charge of +1) and neutrons (with no charge), while the electrons (with a charge of - 1) move around the nucleus in orbits.

Typically the number of positive charges in the nucleus equals the number of negative charges in the orbits. However, as elements lose or gain electrons, they can form ions, or charged atoms. Positively charged ions are called cations, and negatively charged ions are called anions.

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There are a few common misconceptions regarding this atomic theory.

1. Because "the planetary model" is used to represent the orbits of electrons around a nucleus, some people think that electrons travel at a constant rate along a 2-dimensional circle or ellipse, similar to the motion of planets around a sun. Actually, the theory describes a series of different 3-dimensional orbital shapes or clouds in which moving electrons are likely to be found. This misconception could be  reinforced by schematic views of the atom:

Illustration from http://mustsee.org.il/hebrew/yeda2000/atoms/atoms.html

But we should keep in mind that these clouds of probability were found to have non-circular shapes:

Illustration from http://mustsee.org.il/hebrew/yeda2000/atoms/atoms.html

2. Because the proton, neutron, and electron are mentioned in introductory chemistry, some people do not realize that many other subatomic particles have been suggested and supported with evidence. 

"Today all the matter in the universe is viewed as being composed of three kinds of elementary objects: 
(1) particles called quarks, which make up neutrons and protons;
(2) particles called leptons, which include electrons and some similar particles; 
(3) particles called bosons, or vector mesons, which include the photons seen as light and which carry the electromagnetic force. "
http://library.thinkquest.org/22655/atomic_particles.htm

So, your next question is, "What are the different flavors of quarks?" The answer is: up, down, top, bottom, strange, and charm. (Please excuse this slight sidetrip into subatomic physics; it is only mentioned to illustrate how current atomic theory seems to dispel a common myth, and because it sounds weird.)

See also:
www.geocities.com/CapeCanaveral/Hangar/7244/homework/subatom/subatomic.html

See also:
www.gate.net/~zardoz/atom.htm

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Atoms of the same element have the same number of protons in their nuclei. The number of protons is referred to as the atomic number. Unless an atom becomes a ion, or charged, the number of negatively charged electrons in the orbits is equal to the number of positively charged protons in the nucleus. However, the number of neutrons in the nucleus can vary.

For example, Hydrogen has an atomic number of 1, and always has exactly one proton in its nucleus. But some atoms of Hydrogen have no neutrons (Protium), some have one neutron (Deuterium), and some have two neutrons (Tritium). These alternate types of an element created by differing numbers of neutrons are called different isotopes.

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Because the atomic mass of a proton or a neutron is 1 atomic mass unit (amu), the atomic mass of Hydrogen without any neutrons (i.e., Protium) would be very nearly 1 (1.0078 amu). However, because of the percentages of Protium, Deuterium, and Tritium in a sample of Hydrogen, the average atomic mass is just slightly greater than the atomic mass of Protium (1.00794 amu.) These isotopes of Hydrogen have the same chemical properties, but different nuclear properties. The "heavy water" experiments that lead to the thermonuclear bomb used isotopes of Hydrogen. 

One amu is approximately equal to 1.6592 * 10 ^-27 kg. An electron has an atomic mass of 1 / 1840 amu.

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Because it is radioactive, Tritium decays with a half-life of 12.3 years. This means that if there are 8 pounds of tritium in a closed container in the year 2000, by the year 2012 (point three) there will be only 4 pounds of tritium, with the remainder reverting to another isotope of Hydrogen. By 2024.6, there will be only 2 pounds of Tritium. Half of a radioactive material will have decayed in one of its half-life periods.

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Each element has a unique number of protons, as noted above. Each element has a standard name and symbol as well. Sometimes these are intuitive, like H for Hydrogen, sometimes they are not, like Pb for Lead.

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In order to become more familiar with the names and characteristics of elements, it is wise to use a periodic table. This is a two-dimensional graphic representation of all elements, with a different one corresponding to each cell in the table. The table is called periodic because the elements have a special arrangement where they seem to repeat certain properties periodically through the list.

Please visit on any of the following online periodic table of elements. You can find detailed information by clicking on an element's symbol:

• http://www.mcs.net/~ars/spectro/elements.htm
• http://www.chemicalelements.com/
• http://periodic.asterics.com/html4css.html

Notice that Hydrogen is on the top left, and then Helium, with an atomic number of 2, is on the top right. This is because the first orbital shell in an atom can only contain a maximum of two electrons. Typically, Hydrogen has one electron, and Helium has two electrons. The third element, Lithium, has a filled inner shell, and one electron on the next level. If you look down the table beneath Hydrogen and Lithium, you find Sodium (Na), which has two electrons in the first shell, 8 in the second shell, and 1 in the third shell. Hydrogen, Lithium and Sodium, therefore, all have a single electron in their outer shell. Therefore, when they enter into chemical reactions, they tend to readily share that electron with other elements, especially with those that only need one electron to complete their outer shell.

As was said, Helium has a competed outer shell. So do all of the elements directly below it: Neon, Argon, Krypton, Xenon, and Radon. This group of 6 elements tends not to react with other elements because they have competed outer shells with all electrons firmly attracted to the nucleus and no room for additional electrons on existing shells. These elements are therefore known as the noble gasses or the inert gasses. They occupy the column known as Group VIII on the periodic table.

TIG welder, photo from: www.anionics.com/tig_weld.html

Have you ever tried to weld Aluminum with an oxyacetylene torch or with a arc welding rod? If so, you have probably noticed that it is very difficult (but not impossible). This is because when aluminum oxidizes (like when iron rusts), it forms a coating. Aluminum oxide coats the aluminum beneath. However, aluminum oxide has a higher melting temperature than aluminum, making it nearly problematic to weld because the oxide freezes. TIG welding is one solution. TIG stands for Tungsten Inert Gas. It works by heating the base metal with an electric arc between a non-consumable Tungsten electrode and the base metal. An inert gas, usually argon, is continually blown at the weld, forming a shroud around the weld pool. This keeps oxygen out and prevents oxides from forming during welding.

Other columns on the periodic table, called Groups, contain elements that share properties. Group IA, on the left of the table, includes the "Alkaline Metals" Li, Na, K, Rb, Cs, and Fr. They are all silvery-colored metals, but they can be cut with a knife to reveal a lustrous surface that soon tarnishes. Because they have only one electron in their outer shell, they are highly reactive and have a valence of +1.

The Alkaline Metals tend to react readily with the elements in Group VIIB, which are missing only one electron to compete their outer shell. These are the "Halogens," and they include F, Cl, Br, I, and As, each with a valence of -1. When elements bond, they sometimes share or swap electrons according to their valences.

Usually atoms of an element can exist in nature without being bonded to other atoms of the same element. This is not the case for diatoms, were two atoms from the same element bond to produce a molecule. Hydrogen, oxygen, nitrogen and the halogens form diatoms. Thus, when referring to hydrogen gas, it is proper to refer to H₂ rather than H. Also, while typical oxygen is O₂, a special form of oxygen exists where three atoms are bonded: ozone, or O₃.

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The periodic table lets us distinguish between metals and nonmetals, which appear separated by a boundary of metalloids. Boron (B), silicon, germanium, arsenic, antimony, tellurium, and astatine are metalloids. All of the elements to the left of this jagged line on the periodic table are metals (with the exception of Hydrogen); all of the metals to the right are nonmetals. Unlike most nonmetals, metals tend to conduct electricity, be solid at room temperature (except for mercury), be malleable and ductile. Metalloids, also called semi metals, share some properties of metals and some properties of nonmetals.

Sodium metal can kill you, as can chlorine (Cl) gas. But when an atom of sodium (Na) bonds with an atom of chlorine, we get sodium chloride (NaCl), or common table salt. (Yeah, too much of that can kill you, too.)

A compound is formed when there is a chemical bond between elements. The smallest unit of a compound is a molecule. A compound cannot typically be separated into its elements by ordinary physical methods.

But how are atoms held together? There are different types of chemical bonds, primary and secondary. Primary bonds are stronger, and can be further classified as either covalent bonds, ionic bonds, or metallic bonds.

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Covalent Bonds

Covalent bonds involve electron sharing between atoms. When two atoms of chlorine exist as a diatom, they compete each other's outer shell by sharing electrons. This is typical of organic compounds, such as methane and polyethylene.

A single bond involves sharing only one pair of electrons, whereas double and triple bonds involve sharing two or three pairs of electrons. Organic compounds that contain only single bonds between carbon atoms are referred to as saturated; those with double or triple carbon bonds are unsaturated.

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Ionic Bonds

Ionic bonding is electron swapping. Here, some electrons are actually transferred to other elements. This is more typical of inorganic compounds, such as sodium chloride.

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Metallic Bonds

Metals tend to have positive valences; that is, they have just a few electrons in their outer shells, and these are not strongly attracted by the protons in the nucleus. Therefore, metals tend to exhibit a type of bonding where electrons are moving in clouds or swarms throughout the material.

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Secondary Bonds

van der Waals bonds are formed from weak attractive forces. This happens, for example, when the noble gasses are subjected to very low temperatures and condense.

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