Prof Gilbert LECTURE 4 CHEM 1211 Fall 10 Announcements Reminders Homework Assignment 1 is due this Sunday 9 19 My receiver was not working during the Monday Clicker Quiz so we will try again with a similar question at the beginning of class today Last time Ch 1 Dimensional Analysis the key is to make sure that units in the conversion factors are arranged so that the original units cancel out and the desired ones remain Thus an original unit in a numerator should appear in the denominator of one of the conversion factors and vice versa Ch 2 Compound formation We live on a planet with a unique chemical composition because of the presence of ionic and molecular compounds Metals combine with nonmetals to form ionic compounds nonmetals combine with each other and with semi metals to form molecular compounds often gases and solids with extended 3 D arrays of covalently bonded atoms Formulas and Nomenclature of Compounds Formulas of ionic compounds are the simplest ratios of their ions a k a empitical formulas such as CaCl2 Similarly formulas of 3 D arrays of atoms are the simplest ratios of their atoms such as SiO2 Molecular formulas describe the actual of atoms per molecule Names ion and ion ending in ide Use prefixes in names of molecular compounds to distinguish between them CO vs CO2 for example Use Roman numerals to indicate the charges of transition metal ions Oxoanions end in ate or ite depending on of O atoms per ion Use per and hypo prefixes if there are more than 2 oxoanions for a given nonmetal atom CLICKER QUIZ 1 do over This time Dalton s law of multiple proportions Relative mass ratios of the elements in small molecule compounds made of the same elements are simple who numbers Ex ratio of O to C in CO2 is twice what it is in CO Nomenclature acids Examples Oxoacids when the cation is H ate oxoanion turns into ic acid and ite oxoanion turns into ous acid NO3 nitrate H HNO3 nitric acid NO2 nitrite H HNO2 nitrous acid Binary acids hydro acid Ex Name of aqueous HCl is hydrochloric acid Discovery of Sub atomic Particles 1 Electrons J J Thomson s experiments with cathode ray tubes told him that there were the same negatively charged particles in many elements and he was able to calculate the mass charge ratio of these particles 2 Millikans oil drop experiments 1909 the value of the electron s charge and indirectly its mass As for the necessary positive charge in an atom nobody knew where it was until Rutherford and his students irradiated thin gold foil with particles He nuclei and followed where they went The results amazed Rutherford and led him to formulate the modern atomic model on the right above Protons in the nucleus electrons in a cloud around it Neutrons were more elusive and not discovered until the 1930s Some Properties of the Neutron Proton and Electron Particle Neutron Proton Electron Mass amu 1 0087 1 0073 0 0005486 g 1 675x10 24 1 673x10 24 9 109 10 28 Rel Charge 0 1 1 Isotopes One of JJ Thomson s students Fred Aston built a modified cathode ray tube and detected a beam of rays much heavier particles that turned out to be atomic nuclei When the tube contained Ne gas he got 2 beams one with a mass of 20 amu particles and a weaker beam of 22 amu particles the two principal isotopes of Ne 20Ne and 22Ne 2 stable isotopes of H 1H and 2H The neutron gray sphere and protons red spheres are called nucleons The number of protons in the nucleus of an atom defines its atomic number Z The combined number of protons and neutrons equals its mass number A The weighted average of the masses of the isotopes defines the average atomic mass of an element Naturally occurring C is 98 892 1 108 Ave atomic mass 0 98892 12 0000 0 0108 13 00335 12 011 CLICKER QUIZ 2
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