Chapter 3: Atomic Theory and Elements, Atoms, Compounds & Ions A. The Elements All of the materials in the universe can be chemically broken down into about 100 different elements. 1. Element can have several meanings Element Element Element Microscopic form Single atom of that element Macroscopic form Sample of that element large enough to weigh on a balance Generic form When we say the human body contains the element sodium or lithium, we do not mean that free elemental sodium or lithium is present. Rather we mean that atoms of these elements are present in some form. 2. Names and Symbols for the Elements Each element has a name and a symbol. The symbol usually consists of the first one or two letters of the element s name. Examples: Oxygen O Krypton Kr Sometimes the symbol is taken from the element s original Latin or Greek name. Examples: Sodium Na natrium (L. sodium carbonate) Lead Pb plumbum (L. liquid silver) Bromine Br bromos (Gr. stench) 1
B. Compounds Compounds are made by combining atoms of the elements just as words are constructed from the letters in the alphabet. 1. Formulas of Compounds A compound is represented by a chemical formula in which the number and kind of atoms present is shown by using the element symbols and subscripts. Example: the simple sugar, glucose Words Compounds 450 B.C. (Democritus) Greek Philosopher Matter is made up of tiny indivisible particles - ATOM indivisible Modern Definition Smallest particle of an element that retains all chemical and physical properties of that element 2
1808 (Dalton) Original Atomic Theory All elements are composed of atoms All atoms of the same element are the same Atoms of different elements are not alike Original Atomic Theory - Dalton Atoms (matter) cannot be created nor destroyed Chemical Reactions change the arrangement of atoms Law of Constant Composition: a compound always contains the same proportions by mass of the elements. A given compound always has the same number & arrangement of elements Law of Multiple Proportions: different compounds can be made having different combinations of the same elements Solid sphere 1897 (Thomson) Used a Cathode Ray tube identified the presence of a negatively charged particle http://www.chem.uiuc.edu/clcwebsite/cathode.html (this site has a demo - link) 3
Cathode Ray Tube Evidence of a negatively charged component with negative character: The beam (cathode ray) originated from the end connected to the negative charge. The influence of a magnet: the positive end of the magnet attracted the beam AND the negative end of the magnet repelled the beam. Model from Thomson s work Plum Pudding Model - (Atom is a sphere of positive electricity in which electrons are embedded) http://lecture.lite.msu.edu/~mmp/kap29/cd719.htm 1911 (Rutherford) Rutherford s Experiment Shot Alpha particles positively charged (4 amu) at gold foil Prediction: Alpha particles would pass straight through gold foil Observed: Alpha particles were deflected at various angles 1911 (Rutherford) cont d. Conclusion: Nuclear Atom Alpha particles met a large mass that was positively charged within the atom Nucleus - 1 / 100 000 the diameter of the atom (extremely small), massive, positively charged 4
1911 (Rutherford) cont d. (Rutherford) cont d. By 1919 Rutherford introduced the idea that the nucleus contained a particle called the proton Proton: Same magnitude of charge as an electron but opposite in charge (+) 1913 (Bohr s Model) Planetary model - electrons orbit around the nucleus in a specific path Nucleus 1932 (Chadwick) Discovered neutron mass equal to that of a proton but no electrical charge electrons 5
1st Periodic Table Mendeleev 1869 Order was based on atomic masses He noticed that properties of elements repeated Modern Periodic Table Based on Atomic Number for order Based on Electron Configuration (electrons positions in atoms) for arrangement Periodic Table/Periodic Law: When elements are arranged in order of increasing atomic number, their physical & chemical properties show a repeating (periodic) pattern Periods Horizontal Rows 6
Groups and/or Families p.68 Vertical Column(s) Elements in groups/families have similar (not identical) properties Diatomic Molecules: A Group of elements that exist paired when alone & not as a single element: H 2, N 2, O 2, F 2 Cl 2, Br 2, I 2, (7) with At 2 (8) Memorize!!! Metals vs. Nonmetals 1-Luster 2 -Good conductors of heat & electricity 3 -Solids at room temp. (High melting & boiling points) 4 -Malleable 5 -Ductile 6 -Form positive ions 1 -Solids - dull 2 -Poor conductors of heat & electricity 3 -most are Gases @ room temp. (low m.p. & b.p.) 4 & 5 -Solids are brittle 6 -Form negative ions Semimetals or Metalloids B, Si, Ge, As, Sb, Te, Po, At Properties: Luster (metallic) Brittle (nonmetallic) Semiconductors of heat & electricity (intermediate) 7
Subatomic Particle Subatomic Particles Charge Mass Relative Mass Electron Negative 9.11 x 10-28 g 0 amu =.000549 amu Proton Positive 1.673 x 10-24 g 1 amu = 1.00728 amu Neutron Neutral 1.675 x 10-24 g 1 amu = 1.00867 amu Atomic Number number of protons contained in an element Atomic Mass Unit (amu) 1/12 the mass of C-12 atom = 1amu mass of 1 proton or 1 neutron 1 amu Mass Number (atomic mass or atomic weight) The sum of the neutrons & protons in an atom Note: Electrons are not considered in an atoms mass but Electrons determine chemical behavior, reactivity and appearance of the atom 8
Isotopes 2 or more atoms of the same element (same number of protons) but different atomic masses (different numbers of neutrons) Weighted Average Takes into account all isotopes and % abundance Best way to represent an atoms mass Masses on the periodic table are all Weighted Averages Ions Atoms can form ions by gaining or losing electrons. Metals tend to lose one or more electrons to form positive ions called cations. [+ ion is always smaller than the atom] p. 77 Ions Nonmetals tend to gain one or more electrons to form negative ions called anions. [- ion is always larger than the atom] p. 78 Ion is charged atom: ex. K +1, Ca +2, Al +3 Cations are generally named by using the name of the parent atom. Ion is charged atom: ex. F -1, O -2, N -3 Anions are named by using the root of the atom name followed by the suffix ide. 9
Ions Ion Charges and the Periodic Table The ion that a particular atom will form can be predicted from the periodic table. Elements in Group 1 and 2 form 1+ and 2+ ions, respectively Group 7 atoms form anions with 1- charges Group 6 atoms form anions with 2- charges Ions Ion Charges and the Periodic Table p.79 10