Matter

November 15, 2011, 9:47 am

Matter is the material that makes up objects in the Universe. All matter on the Earth is constructed of elements (see periodic table of elements). Chemists have described approximately 115 different elements. Each of these elements have distinct chemical characteristics. Table 1 lists some of the chemical characteristics for 48 common elements found in the Earth's continental crust.

The smallest particle that exhibits the unique chemical characteristics of an element is known as an atom. Atoms are composed of yet smaller particles known as protons, neutrons, and electrons. A proton is a subatomic particle that has significant mass and contributes a single positive electrical charge to an atom. Neutrons also have significant mass but no electrical charge. Electrons are extremely light subatomic particles having a mass that is 1/1840 of a proton. Each electron also has a negative electrical charge.

Protons and neutrons make up the nucleus of an atom. As a result, most of an atom's mass is concentrated in the nucleus. Because protons are positively charged, the nucleus has a positive charge equal to the number of these subatomic particles. Electrons are found orbiting outside the nucleus at various distances based on their energy level. The area occupied by the electrons has a negative charge equal to the number of these subatomic particles. If an atom has an equal number of electrons and protons its net electrical charge is zero. If there are more electrons than protons the charge of the atom is negative. Likewise, if there are less electrons than protons the charge of the atom is positive. In both cases, the exact charge is determined by subtracting protons from electrons. As a result, 4 protons minus 6 electrons give an atomic charge of -2.

The number of protons found in the nuclei of the different types of elements is unique and is referred to as the atomic number (Table 1). All atoms of a specific element have the same number of protons in their nuclei. Atomic mass number is an atom's total number of neutrons and protons. Many elements have unequal numbers of neutrons and protons in their nucleus. An element's atomic weight refers to the total weight of neutrons, protons, and electrons. For example, the atomic weight of aluminum is 26.98 (Table 1). Atomic number describes the number of protons found in an atom. For example, silver has an atomic number of 47 since it has 47 protons in its atom (Table 1). Some elements can have variants containing different numbers of neutrons but similar numbers of protons. We call these variants isotopes. Carbon has two isotopes. Its most common form is carbon-12 which has 6 protons plus 6 neutrons. About 99% of the carbon on our planet is of this type. The isotope carbon-13 has 6 protons plus 7 neutrons. Carbon-14 is the rarest isotope of carbon containing 8 neutrons. Some isotopes are unstable and their nucleus tends to lose subatomic particles forming an element with a lower atomic mass. This process is known as radioactive decay.

Table 1: Characteristics of some of the common chemical elements found in the Earth's continental crust.


Element Chemical
Symbol
Atomic
Number
Common Atomic
Mass Number
Atomic
Weight
Percent in
Continental Crust
Required for
all Life
Required for
Some Lifeforms
Element
Type
Moderately
Toxic
Extremely
Toxic
Aluminum Al 13 27 26.98 8.2300 - X Metalloid - -
Antimony Sb 51 122 121.75 0.00002 - - Metalloid - -
Arsenic As 33 75 74.92 0.00018 - - Metalloid - X
Barium Ba 56 137 137.34 0.0425 - - Metal - -
Beryllium Be 4 10 9.01 0.00028 - - Metal - X
Bismuth Bi 83 209 208.98 0.000017 - - Metal - -
Boron B 5 11 10.81 0.0010 - - Metalloid - -
Bromine Br 35 80 79.91 0.00025 - - Nonmetal - -
Cadmium Cd 48 112 112.40 0.00002 - - Metal - X
Calcium Ca 20 40 40.08 4.1000 X - Metal - -
Carbon C 6 12 12.01 0.0200 X - Nonmetal - -
Chlorine Cl 17 35.5 35.45 0.0130 - X Nonmetal X -
Chromium Cr 24 52 52.00 0.0100 - - Metal X -
Cobalt Co 27 59 58.93 0.0025 - X Metal - -
Copper Cu 29 63.5 63.54 0.0055 X - Metal X -
Fluorine F 9 19 19.00 0.0625 - X Nonmetal X -
Gallium Ga 31 70 69.72 0.0015 - - Metal - -
Germanium Ge 32 73 72.59 0.00015 - - Metalloid - -
Gold Au 79 197 196.97 0.0000004 - - Metal - -
Hydrogen H 1 1 1.008 1.4000 X - Nonmetal - -
Iodine I 53 127 126.90 0.00005 - X Nonmetal - -
Iron Fe 26 56 55.85 5.6000 X - Metal - -
Lead Pb 82 207 207.19 0.00125 - - Metal - X
Lithium Li 3 6 6.94 0.0020 - - Metal - -
Magnesium Mg 12 24 24.31 2.3000 X - Metal - -
Manganese Mn 25 55 54.94 0.0950 X - Metal - -
Mercury Hg 80 201 200.59 0.000008 - - Metal - X
Molybdenum Mo 42 96 95.94 0.00015 X - Metal - -
Nickel Ni 28 59 58.71 0.0075 - - Metal - X
Nitrogen N 7 14 14.01 0.0020 X - Nonmetal - -
Oxygen O 8 16 16.00 46.4000 X - Nonmetal - -
Palladium Pd 46 106 106.40 0.000001 - - Metal X -
Phosphorus P 15 31 30.97 0.1050 X - Nonmetal - -
Platinum Pt 78 195 195.09 0.0000005 - - Metal - -
Potassium K 19 39 39.10 2.1000 X - Metal - -
Rubidium Rb 37 85.5 85.47 0.0090 - - Metal - -
Selenium Se 34 79 78.96 0.000005 - X Nonmetal X -
Silicon Si 14 28 28.09 28.2000 - - Metalloid - -
Silver Ag 47 108 107.87 0.000007 - - Metal - X
Sodium Na 11 23 22.99 2.4000 - X Metal - -
Sulfur S 16 32 32.06 0.0260 X - Nonmetal - -
Thorium Th 90 232 232.04 0.00096 - - - - -
Tin Sn 50 119 118.69 0.00020 - - Metal X -
Titanium Ti 22 48 47.90 0.5700 - - Metal - -
Tungsten W 74 184 183.85 0.00015 - - Metal - -
Uranium U 92 238 238.03 0.00027 - - - - -
Vanadium V 23 51 50.94 0.0135 - X Metal X -
Zinc Zn 30 65 65.37 0.0070 X - Metal - -


Elements can be classified as being either metals, nonmetals, or metalloids (Table 1). Metals are elements that usually conduct heat and electricity and are shiny. Nonmetals do not conduct electricity as well and are normally not shiny. Metalloids have characteristics that are in between metals and nonmetals.

caption Figure 1: Some common molecules and compounds. The molecules in the top row bond with each other by sharing electrons. The compounds in the bottom row also share electrons. However, these joins are called ionic bonds. (Source: PhysicalGeography.net)

Elements with a net positive or negative charge are called ions. Chemists indicate the number of positive or negative charges on an ion using a superscript after the element's symbol. For example, calcium has two positive charges and is written as Ca2+. Some common negatively charged ions include nitrate (NO3-), sulfate (SO42-), and phosphate (PO43-).

caption Figure 2: Atomic representation of sodium chloride or table salt. This compound forms in nature as a highly ordered, three-dimensional network of oppositely charged ions. The bonds that form between the sodium (Na+) and (Cl-) chloride ions give this compound great internal strength allowing it to form large crystals. (Source: PhysicalGeography.net)

Positive and negative ions are electrically attracted to each other. This mutual attraction allows for the bonding of atoms to occur forming structures of matter that are larger than just one atom. When similar atoms bond together they construct molecules. Atoms of different elements joined together form compounds (Figure 1). Sodium chloride (or table salt), is an ionic compound consisting of sodium (Na+) and chloride (Cl-). In nature, it forms as a three-dimensional array of oppositely charged ions (Figure 2). Many of the Earth's substances have a molecular structure similar to sodium chloride.


Further Reading: PhysicalGeography.net

Glossary

Citation

Pidwirny, M. (2011). Matter. Retrieved from http://www.eoearth.org/view/article/154518

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