Law of Conservation of MassLavoisier (1743-1794) In a chemical reaction, matter is neither created nor destroyed. P. 57 Click on picture for movie
CuCO3(s) CuO(s) + CO2(g) 123.6 g 79.6 g ? g
CuCO3(s) CuO(s) + CO2(g) 123.6 g 79.6 g 44.0 g
CuCO3(s) CuO(s) + CO2(g) 123.6 g 79.6 g 44.0 g 123.6 g = 79.6 g + 44.0 g
Law of Definite ProportionsProost (1754-1826) Different samples of any pure compound contain the same elements in the same proportions by mass. P. 58
Mass Ratio of Cu:O:C in copper carbonate Cu:O:C = 53:40:10 = 5.3 : 4: 1 Regardless of where the copper carbonate is found
Mass Ratio of Cu:O:C in copper carbonate Cu:O:C = 53:40:10 = 5.3 : 4: 1 If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain?
Mass Ratio of Cu:O:C in copper carbonate Cu:O:C = 53:40:10 = 5.3 : 4: 1 If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain? Cu / C = 5.3g / 1g = x / 20g
Mass Ratio of Cu:O:C in copper carbonate Cu:O:C = 53:40:10 = 5.3 : 4: 1 If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain? (5.3g / 1g)20g = x
Mass Ratio of Cu:O:C in copper carbonate Cu:O:C = 53:40:10 = 5.3 : 4: 1 If a sample of copper carbonate contains 20 g of carbon how many g of Cu will it contain? 106 g = x
Law of Multiple Proportions (John Dalton) • The masses of one element that can combine chemically with a fixed mass of another element are in a ratio of small whole numbers. 2C + O22CO Carbon monoxide C + O2 CO2 Carbon dioxide 24 g 32 g 2:1 12 g 32 g P. 59
The idea of “whole numbers” suggests the presence of “individual” particleATOMS !
Dalton’s Atomic Theory John Dalton (1766-1844) proposed an atomic theory • matter is composed, indivisible particles (atoms). • all atoms of a particular element are identical • different elements have different atoms • atoms combine in certain whole-number ratios • In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. P. 56-57
OK! Matter is made of ATOMSBut what are ATOMS?What are ATOMS themselves made of?
Cathode–Ray Tube P. 61
Mass of an electron • Experiments performed by Thompson together with those of Robert Millikan were able to show that an electron has a mass of • 9.1 x 10-28 g • The mass of one atom of the lightest element, hydrogen, is 1.7 x 10-24 g • An electron is approx 1/2000th the mass of a H atom!
So the electron appears to be an insignificant part of the atom - from a mass point of view!How are electrons arranged inside an atom?
Thompson’s Plum Pudding Model of the Atom electron Diffuse positive charge
Ernest Rutherford (1871-1937)
Nucleus of the AtomRutherford (1871-1937) P. 64 Click on picture for movie
Nucleus of the Atom Continued (Rutherford) • At the center of the atom is a very densenucleus that accounts for almost all the mass of the atom and contains all the positive charge. • He named these positive particles protons. • Protons have a relative mass of 1 and a charge of +1. P. 64
Nucleus of the AtomChadwick (1891-1974) • When atoms of beryllium were bombarded with alpha particles, new uncharged particles with mass identical to protons were emitted. • These uncharged particles were called neutrons. • Neutrons have a relative mass of 1 and a charge of zero. P. 64-65
Our first direct look at the atomic world Get me out of here!
Isotopes • Atoms of an element that have the same number of protons but different numbers of neutrons are called isotopes. AXX = symbol of element ZA = mass number Z = atomic number • The isotopes of sulfur are written: 32 S33S34 S36 S 16 16 16 16
Isotopes Continued Which of the following represent isotopes of the same element? Which element? 234X234 X235X238 X 92939292
Answer: 234 U234 Np235 U238U 92939292 234 Np is not an isotope of Uranium. 93
Isotopes of Carbon 12C13 C14C 666
Isotopes of Carbon 12C13 C14C 666 12 - 6 = 6 neutrons 13 - 6 = 7 neutrons 14 - 6 = 8 neutrons Radioactive
Carbon-14 Dating • Used to date archeological artifacts up to 60000 years old • measures amount of radioactive 14C left in a sample • Amount of 14C decreases with time • will be discussed in detail in Ch 5
Isotopic Fingerprinting • The ratio of stable isotopes (e.g. 13C/12C) in a substance will vary slightly depending on the origin of the substance • for example, petroleum samples from different parts of the world will have different 13C/12C ratios • How could such information be useful?
Periodic TableMendeleev (1834-1907) • Atoms arranged by ascending atomic number • Horizontal rows called periods • Vertical columns called groups • Elements within a group have similar chemical properties
Metals Metals have distinctive properties • Good conductors of heat and electricity • Shiny appearance • Ductile and malleable • Are light purple in periodic table that is on the inside cover of the book
Nonmetals • Do not conduct heat or electricity • Not ductile or malleable • Many exist as gases • Are green in periodic table that is on the inside cover of the book