Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 2 Atoms, Molecules, and Ions Honors Chemistry 1 “We are each so atomically numerous and so vigorously recycled at death that a significant number of our atoms – up to a billion for each of us, probably once belonged to Shakespeare. A billion more each came from Buddha and Genghis Khan and Beethoven and …” Bill Bryson Cont. Aristotle (Greek, 384322 B.C.) – did NOT believe in atoms NO experimentation history Democritus (Greek, 460-370 B.C.) – basic particle of matter atom NO experimentation Cont. John Dalton (English, 1803) – Dalton’s Atomic Theory Dalton’s Atomic Theory 1. All matter composed of atoms 2. Atoms of given element identical (e.g.size, mass) – atoms of diff. elements differ 3. Atoms can not be subdivided, created, or destroyed 4. Atoms of diff. elements combine in simple whole number ratios cmpds. 5. Atoms combine, separate, or rearrange in chem. reactions # 2, 3 now revised History review Ancient cultures present day Philosophy < > Science Role of experimentation What is a theory Conservation of mass A + B 1 mass unit + 3 mass units AB 4 mass units A + 1 mass unit + AB 4 mass units B 3 mass units Law of multiple proportion If 2 or more diff. cmpds. are composed of the same 2 elements, the masses of 2nd element combined w/ a certain mass of the 1st element can be expressed as ratios of sm. whole numbers e.g. CO 12 g C + 16 g O CO2 12 g C + 32 g O 16:32 = 1:2 Structure of the atom Atom – smallest particle of an element that can exist either alone or in combination w/ other atoms STM images Discovery of the electron (e ) J.J. Thomson (1897) Cathode ray tube (CRT) Thomson measured chg./ mass ratio of charged particles CRT (cathode ray tube) The cathode ray tube (CRT), invented by German physicist Karl Ferdinand Braun in 1879, is an evacuated glass envelope containing an electron gun (a source of electrons) and a fluorescent screen, usually with internal or external means to accelerate and deflect the electrons. When electrons strike the fluorescent screen, light is emitted. Thomson (CRT) Electrons have a neg. (-) chg Have a very small mass 9.109 x 10-28 g = (0.0000000000000000000000000009109 g) Discovery of atomic nucleus Rutherford, Geiger, Marsden (1908, 1909) Used (+) charged particle beam aimed at metal foil Gold foil experiment Possible results: Atoms have subatomic particles, Ernest Rutherford. Students will be divided into two groups, atoms and alpha particles. “Atoms” will line up with their arms outstretched, touching only fingertips. “Alpha Particles” will first find a partner and stand shoulder to shoulder. Groups of “alpha particles” will line up behind one another. I will direct the “particles” to travel through the “atoms.” Repeat with a second “layer” of atoms Rutherford: the nucleus (+) chg. Dense central core of atom Contains nearly all mass of atom Atomic nucleus 2 types of particles: Protons, (+) chg, mass= 1.673x10-24g Neutrons, neutral chg, mass= 1.675x10-24g Discovery of the neutron Chadwick, (1932), England “Had the neutron been isolated in the 1920s (when work was started) it is very likely the atomic bomb would have been developed in Europe, undoubtedly by the Germans” Bill Bryson symbols Electron : e Proton : p+ Neutron : no Isotopes of hydrogen Protium: 1 p+, 1 e Deuterium: 1 p+, 1 e-, 1 n0 Tritium: 1 p+, 1 e-, 2 n0 (radioactive) Atomic number # of p+ in nucleus Mass number # of p+ and n0 in nucleus Isotopes Different forms of the same element with different mass Same # p+ Diff. # n0 Carbon Dating Isotopes of hydrogen Atomic # Neutron # mass# protium 1 0 1 deuterium 1 1 2 tritium 1 2 3 2 ways of writing isotopes (examples) Carbon-12, uranium-235 ( the 12 & the 235 are the mass numbers, e.g. U-235 has 92 p+ and 143 n0) 235 (235 is mass #, 92 is atomic #) 92 U Relative atomic mass The mass of carbon-12 is exactly 12 atomic mass units (u) This is a defined standard The mass of all other atoms are expressed relative to carbon-12 Mass # v. Atomic mass Isotope Mass # Atomic mass Oxygen-16 16 15.994 Copper-63 63 62.939 Avg. Atomic Mass (atomic weight) Weighted avg. of atomic masses of naturally occurring isotopes of an element e.g. : naturally occurring Cu 69.17% Cu-63 (atomic mass 62.939) 30.83% Cu-65 (atomic mass 64.927) (0.6917)(62.939)+(0.3083)(64.927) = 63.546 Found on periodic table The Periodic Table 5 minute history of chemistry Aristotle’s elements Air Water Fire Earth Alchemy Alchemy symbols Origin of modern element symbols (examples) e.g. carbon, symbol C, from the Latin word "carbo" meaning "charcoal" e.g. lead, symbol Pb, the origin of the symbol Pb is the Latin word "plumbum" e.g. mercury, symbol Hg, the origin of the symbol Hg is the Latin word "hydrargyrum" meaning "liquid silver" e.g., Bismuth, symbol Bi, from the German word "bisemutum" History (cont.) Dmitri Mendeleev His first periodic table published in 1869 Mendeleev’s periodic table Left empty spaces for elements not yet discovered When these were later discovered they ‘fit’ almost perfectly e.g. scandium Modifications continue……… Element symbols One or two letter symbols First letter uppercase, e.g. Fe, C Second letter (if present) lowercase, e.g. Ca Periodic table An arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column Groups: vertical Periods: horizontal Alkali metals (group 1) Extremely reactive Not found as free elements in nature e.g. potassium Alkaline-Earth metals (group 2) Reactive (not as reactive as grp 1) e.g. Mg, Ca Transition elements (groups 3-12) Metals, e.g. Cu, Ag, Fe Good conductors Less reactive that grps 1, 2 Halogens (group 17) Most reactive nonmetals, e.g. Br, I React w/ metals to form salts e.g. 2K + Cl2 2 KCl Noble gases (grp 18) Non reactive e.g. Xe, Kr Trends Electronegativity Ability to attract electrons Atomic radius Sub level blocks Monatomic ions Ion with a single atom e.g. Na+, Cl- Polyatomic ions Ions w/ more than one atom e.g. SO42-, NO3- Ionic Compounds Na+ + Cl- NaCl Mg2+ + Cl- Cl- MgCl2 Al3+ Al3+ + O2- O2- O2- ? Naming Ionic Compounds NaCl Sodium Chloride Name of metallic ion first + root name of nonmetal + ide Metals that form more than one ion use roman numerals as part of the name e.g. copper I Cu+ copper II Cu2+ e.g. Cu(NO3)2 – copper II nitrate Polyatomic ions e.g. ammonium ion NH4+ Al3+ & SO42 Al3+ Al3+ SO42- SO42- SO42 Al2(SO4)3 aluminum sulfate Prefixes 1 - mono 2 – di 3 – tri 4 – tetra 5 – penta 6 – hexa 7 – hepta 8 – octa Molecular compounds (examples) CCl4 carbon tetrachloride N 2O 3 dinitrogen trioxide Acids Sulfuric H2SO4 Hydrochloric HCl Nitric HNO3 Phosphoric H3PO4 Acetic HC2H3O2 Hydrofluoric HF Carbonic H2CO3 Diatomic molecules ClIF H BrON Cl2 I2 F2 H2 Br2 O2 N2 Formula mass, molar mass, formula weight (F. W.) E.g. CaCl2 1 Ca atom x 40.078u / Ca atom = 40.078u 2 Cl atoms x 35.453u / Cl atom = 70.906u + ________ formula mass CaCl2 = 110.984u