What do those chemical symbols and equations mean?

Transcription

1 What do those chemical symbols and equations mean? Introduction As we discuss the composition of the atmosphere, the ozone hole and pollution, we will be using chemical symbols and various equations. Thus, this lab exercise will provide the basics of chemical notation so you will be able to understand the shorthand you will encounter in the class and textbook. What are elements, mixtures and compounds? Elements An element is a substance that has not been decomposed into a simpler substance by chemical reactions. At this time, there are just over a hundred elements. Some of these known elements have been created in laboratories and have not been found in nature. Examples of elements include aluminum, iron, sulfur, oxygen and carbon. Compounds A compound is a homogeneous substance that consists of atoms of more than one element the atoms of which are chemically bonded. Salt (atoms of sodium and chlorine) and water (atoms of hydrogen and oxygen) are two common compounds. Note compounds can be chemically decomposed into their component elements. Mixtures A mixture is a blend of various substances, intermingled together. These substances are not chemically bonded together, but are simply mixed together. Note mixtures are not necessarily homogeneous. The atmosphere is an example of a mixture of gases, both elements and compounds. Chemical Symbols As a shorthand nomenclature each element has been assigned an abbreviation to denote the element. These abbreviations are frequently the first one or two letters of the element name. For example, the symbol C denotes carbon, H hydrogen and Ca calcium. These are some of the more obvious symbols. Other elements have less obvious symbols. For example, Fe denotes iron, Cu copper, Au gold and Ag silver. These symbols reflect that at the time the use of symbols was proposed by J.J. Berzelius (1819), these elements were know by their Latin names; ferrum, cuprum, aurum, and argentum, respectively. The elements are frequently displayed in a table called the Periodic Table. See the two sidewalls of the lecture hall to see a full-sized example of the Periodic Table. Below is a simplified version. The Russian chemist, Dmitri Mendeleeff suggested this arrangement of elements in 1869.

2 The elements are more or less arranged left-to-right and top-to-bottom from the least massive, hydrogen, to the most massive atom on this Table, Ununquadium. The number above the element s symbol denotes the element s atomic number, i.e., the number of protons in the nucleus of the element. Below is a list of the chemical elements sorted by atomic number. Note there are a couple of elements in the list that are not included on the Periodic Table above. New elements are being created every once in a while. For example, the element Uuq was created in Some of the other elements included in the list below, but not included in the above Table have been predicted to exist, but have not yet been found or created. Atomic Number Name Symbol 1 Hydrogen H 2 Helium He 3 Lithium Li 4 Beryllium Be 5 Boron B 6 Carbon C 7 Nitrogen N 8 Oxygen O 9 Fluorine F 10 Neon Ne 11 Sodium Na 12 Magnesium Mg

3 13 Aluminum Al 14 Silicon Si 15 Phosphorus P 16 Sulfur S 17 Chlorine Cl 18 Argon Ar 19 Potassium K 20 Calcium Ca 21 Scandium Sc 22 Titanium Ti 23 Vanadium V 24 Chromium Cr 25 Manganese Mn 26 Iron Fe 27 Cobalt Co 28 Nickel Ni 29 Copper Cu 30 Zinc Zn 31 Gallium Ga 32 Germanium Ge 33 Arsenic As 34 Selenium Se 35 Bromine Br 36 Krypton Kr 37 Rubidium Rb 38 Strontium Sr 39 Yttrium Y 40 Zirconium Zr 41 Niobium Nb 42 Molybdenum Mo 43 Technetium Tc 44 Ruthenium Ru 45 Rhodium Rh 46 Palladium Pd 47 Silver Ag 48 Cadmium Cd 49 Indium In 50 Tin Sn 51 Antimony Sb 52 Tellurium Te 53 Iodine I 54 Xenon Xe 55 Cesium Cs 56 Barium Ba 57 Lanthanum La 58 Cerium Ce Climate and Global Change

4 59 Praseodymium Pr 60 Neodymium Nd 61 Promethium Pm 62 Samarium Sm 63 Europium Eu 64 Gadolinium Gd 65 Terbium Tb 66 Dysprosium Dy 67 Holmium Ho 68 Erbium Er 69 Thulium Tm 70 Ytterbium Yb 71 Lutetium Lu 72 Hafnium Hf 73 Tantalum Ta 74 Tungsten W 75 Rhenium Re 76 Osmium Os 77 Iridium Ir 78 Platinum Pt 79 Gold Au 80 Mercury Hg 81 Thallium Tl 82 Lead Pb 83 Bismuth Bi 84 Polonium Po 85 Astatine At 86 Radon Rn 87 Francium Fr 88 Radium Ra 89 Actinium Ac 90 Thorium Th 91 Protactinium Pa 92 Uranium U 93 Neptunium Np 94 Plutonium Pu 95 Americium Am 96 Curium Cm 97 Berkelium Bk 98 Californium Cf 99 Einsteinium Es 100 Fermium Fm 101 Mendelevium Md 102 Nobelium No 103 Lawrencium Lr 104 Rutherfordium Rf Climate and Global Change

5 Exercise 105 Dubnium Db 106 Seaborgium Sg 107 Bohrium Bh 108 Hassium Hs 109 Meitnerium Mt 110 Darmstadtium Ds 111 Roentgenium Rg 112 Ununbium Uub 113 Ununtrium Uut 114 Ununquadium Uuq 115 Ununpentium Uup 116 Ununhexium Uuh 117 Ununseptium Uus 118 Ununoctium Uuo Complete the table below by filling in the empty cells. Element Helium Nitrogen Silicon Radon Chemical Symbol Pb Zn F U Chemical Formulas Besides being a convenient shorthand method of referring to elements, chemical symbols are used to denote the number and type of atoms that make up a molecule of a substance, i.e., the substance s chemical formula. This notation allows the chemist to represent the building blocks, the number of atoms of the elements contained within a molecule of an element or compound. For example, a molecule of the element oxygen is made of two atoms of oxygen, and thus is represented by the symbol, O 2. A molecule of the compound water contains two atoms of hydrogen and one atom of oxygen, and thus is represented by the symbol, H 2 O. The small subscript indicates the number of atoms of an element that are contained in a molecule of a substance. If there is no subscript, it means there is one atom of the element. Below are some additional examples:

6 Exercise A molecule of the compound carbon dioxide contains one atom of carbon and two atoms of oxygen and is denoted symbolically as CO 2. A molecule of sodium bicarbonate (baking soda) is represented by NaHCO 3, i.e., one atom of Na (sodium), one atom of H (hydrogen), one atom of C (carbon) and three atoms of O (oxygen). A molecule of acetylsalicylic acid (aspirin) is symbolically represented by C 9 H 8 O 4. Complete the table below by filling in the empty cells. Compound Hydrogen Sulfide (H 2 S) Carbon Monoxide (CO) Sulfur Dioxide (SO 2 ) Heptane (C 7 H 16 ) Methane (CH 4 ) Constituents and Number of Atoms of Each Chemical Equations A chemical equation represents a chemical reaction, i.e., it describes how reactants (left-hand side of the equation) produce new chemicals or products (right-hand side of the equation). The chemical equation 2H 2 +O 2 2H 2 O represents the reaction of hydrogen and oxygen to form water. The arrow points in the direction of the reaction from the reactants (substances that react) toward the product or products. In this case the reactants are hydrogen (written H 2 because each molecule consists of two atoms of hydrogen) and oxygen (written O 2 because each molecule consists of two atoms of oxygen) and the product is water. The coefficient 2 before the H 2 indicates that two molecules of hydrogen take part in the reaction, and the 2 before the H 2 O indicates that two molecules of water are produced. When no number is written, as in front of the O 2, a one is assumed; one molecule of oxygen takes part in the reaction. The equation shows that two molecules of hydrogen react with one molecule of oxygen to form two molecules of water. Note mass is conserved in this reaction in that there are the same number of atoms of hydrogen (4) and oxygen (2) present on each side of the equation. This is a must for correct chemical equations.

7 Exercise Complete the table below. uv is the abbreviation for ultraviolet light, NO is nitric oxide, NO 2 is nitrous oxide, C 7 H 16 is a form of gasoline. Equation 2H 2 O + uv 2H 2 + O 2 Reactants and Number of Molecules of Each Products and Number of Molecules of Each O 3 + NO NO 2 + O 2 C 7 H O 2 7 CO 2 +8 H 2 O