2 By the end of the chapter you WILL be able to… Describe Democritus’s ideas about atomsExplain Daltons atomic theoryID the special instruments necessary to observe individual atomsID 3 types of subatomic particlesDescribe the structure of atoms according to the Rutherford atomic modelExplain what makes elements and isotopes different from each otherCalculate the number of neutrons in an atomCalculate atomic mass of an element
3 Quantum Model of the Atom Currently the most accepted model“shells” represent areas of probability of finding an electronHere are the majorcontributors…
4 Erwin Schrødingereducated in Vienna; serves in Austrian Army in WWI1926 publishes “wave equation” model of electronsGoes to Germany in 1927 but leaves in 1933 with rise of Nazis; ends up in Austria in 1937; recants opposition to Nazis but is harassed and escapes in 19381933 Nobel Prize in Physics with Dirac1940 establishes Institute for Advanced Studies in DublinNOTE: Schrodinger regretted his “recant” and personally apologized to Einstein after the warNOTE: (Wickipedia) S. lived with 2 women most of his life and this unconventional lifestyle probably contributed to his moving around to many universities in the 1920s and ‘30s
5 Werner Heisenberg 1901-1976 1923 PhD in Munich 1924-’25 works with Bohr in Copenhagenestablishes “quantum mechanics” when only 23 years old in includes Uncertainty Principle1932 Nobel Prize in Physics1941 director of Kaiser Wilhelm Institute in Berlin - captured by US troops at end of WWII & sent to England; returns to Germany after the warPhoto:Text: “Heisenberg's name will always be associated with his theory of quantum mechanics, published in 1925, when he was only 23 years old. …His new theory was based only on what can be observed, that is to say, on the radiation emitted by the atom. We cannot, he said, always assign to an electron a position in space at a given time, nor follow it in its orbit, so that we cannot assume that the planetary orbits postulated by Niels Bohr actually exist. Mechanical quantities, such as position, velocity, etc. should be represented, not by ordinary numbers, but by abstract mathematical structures called "matrices" and he formulated his new theory in terms of matrix equations.”
6 Prince Louis-Victor deBroglie 1892-1987 educated and worked in France - BA in 1913 & graduate work after serving for France in WWIhis 1924 doctoral thesis introduced “wave mechanics” - the idea that the electron could be treated as a wave1929 Nobel Prize in PhysicsPhoto:
7 computer-generated images of “electron cloud” shapes generated by Schrødinger’s wave equationmeta-synthesis(chem education co.)
9 Bohr’s ModelCharacterized by its concentric circles Bohr’s model has probably been ingrained into your headsHowever Bohr was not the first to hypothesize this model
10 The Rutherford Atomic Model Based on his experimental evidence:The atom is mostly empty spaceAll the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”The nucleus is composed of protons and neutronsThe electrons distributed around the nucleus, and occupy most of the volumeHis model was called a “nuclear model”
11 Ernest Rutherford’s Gold Foil Experiment - 1911 Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foilParticle that hit on the detecting screen (film) are recorded
12 Rutherford’s problem: In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?Target #2Target #1
14 Rutherford’s Findings Most of the particles passed right throughA few particles were deflectedVERY FEW were greatly deflected“Like howitzer shells bouncing off of tissue paper!”Conclusions:The nucleus is smallThe nucleus is denseThe nucleus is positively charged
15 Thomson’s Atomic Model J. J. ThomsonThomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.
16 John Dalton ( )Published in 1808, Dalton’s work became the basis for modern atomic theory.Represented the atom as a simple sphere with no internal structure. Sketch it!Showed that substances were combinations of relatively few elements
17 Dalton’s Atomic Theory Includes four partsAll elements are composed of atomsAtoms of the same element are identicalAtoms of different elements can physically mix, or can chemically combine to form compoundsChemical reactions occur when atoms are separated, joined, or combined. (atoms of one element cannot change into another element as a result of a chemical reaction)See diagram on page 102
18 Structure of the Nuclear Atom One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles:Electrons, protons, and neutrons are examples of these fundamental particlesThere are many other types of particles, but we will study these three
19 Democritus of Abdera 460 B.C.E.-370 B.C.E. Believed atoms were indivisible and indestructibleBelieved matter was composed of atoms, the smallest part of an element which retains its identity during a chemical reaction.Atom comes from the Greek work atomos, meaning indivisible .Why is the word “atom” a misnomer?
21 Foundations of Atomic Theory Atoms and the Law of Conservation of Mass… (state it)Atoms have mass, cannot be broken down, and you CAN put them togetherTherefore… A + B C and C A+B(synthesis) (decomposition)What can we say about the masses of the reactants and products?
23 Sizing up the AtomRadii of most atoms fall within the range of 5x10-11 to 2x10-10mThe unit, Angstrom (Å), can be used when dealing with atomic radii. (1x10-10m)Nanometers are also commonly used (1x10-9m)Using the factor label method convert the above measurements to angstroms.You should have gotten….5 – 2 Å How many nanometers?
24 Despite their small size atoms are observable with instruments such as the scanning tunneling microscopeFirst done in 1981When observed they look like this
25 Problem!A sample of copper with a mass of 63.5g contains 6.02x1023 atoms. What is the mass of a single atom of Cu?Answer…1.05x10-22gTHINK ABOUT THIS!!!!!!!!!!!!!!!!-If you lined up 100,000,000 Cu atoms side by side they would only measure 1cm long
27 Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electronSee pages 104 and 105
28 Some Modern Cathode Ray Tubes Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
29 Mass of the ElectronMass of the electron is9.11 x gThe oil drop apparatus1916 – Robert Millikan determines the mass of the electron: 1/1840 the mass of a hydrogen atom; has one unit of negative charge
31 Conclusions from the Study of the Electron: Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electronsElectrons have so little mass that atoms must contain other particles that account for most of the mass
32 Conclusions from the Study of the Electron: Eugen Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron)1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton
33 Subatomic Particles Particle Charge Mass (g) Location Electron (e-) -1 9.11 x 10-28Electron cloudProton (p+)+11.67 x 10-24NucleusNeutron(no)
34 # protons in an atom = # electrons Atomic NumberAtoms are composed of protons, neutrons, and electronsHow then are atoms of one element different from another element?Elements are different because they contain different numbers of PROTONSThe “atomic number” of an element is the number of protons in the nucleus# protons in an atom = # electrons
35 Atomic NumberAtomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.Element# of protonsAtomic # (Z)Carbon6Phosphorus15Gold79
36 IsotopesDalton (thinking back to his theory) was wrong about all elements of the same type being identicalAtoms of the same element can have different numbers of neutrons.Thus, different mass numbers.These are called isotopes.
37 Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons.
38 Naming IsotopesWe can also put the mass number after the name of the element: nuclides…carbon-12carbon-14uranium-235
39 Mass NumberMass number is the number of protons and neutrons in the nucleus of an isotope:Mass # = p+ + n0Nuclidep+n0e-Mass #Oxygen -10-3342- 3115188818Arsenic753375Phosphorus161531
40 Nuclear SymbolsContain the symbol of the element, the mass number and the atomic number.MassnumberXSuperscript →AtomicnumberSubscript →
41 Br Symbols 80 35 Find each of these: number of protons number of neutronsnumber of electronsAtomic numberMass Number80Br35
42 SymbolsIf an element has an atomic number of 34 and a mass number of 78, what is the:number of protonsnumber of neutronsnumber of electronscomplete symbol
43 SymbolsIf an element has 91 protons and 140 neutrons what is theAtomic numberMass numbernumber of electronscomplete symbol
44 SymbolsIf an element has 78 electrons and 117 neutrons what is theAtomic numberMass numbernumber of protonscomplete symbol
45 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. ProtonsElectronsNeutronsNucleusHydrogen–1(protium)1Hydrogen-2(deuterium)Hydrogen-3(tritium)2
46 Atomic Mass How heavy is an atom of oxygen? It depends, because there are different kinds of oxygen atoms.We are more concerned with the average atomic mass.This is based on the abundance (percentage) of each variety of that element in nature.We don’t use grams for this mass because the numbers would be too small.
47 Measuring Atomic MassInstead of grams, the unit we use is the Atomic Mass Unit (amu)It is defined as one-twelfth the mass of a carbon-12 atom.Carbon-12 chosen because of its isotope purity.Each isotope has its own atomic mass, thus we determine the average from percent abundance.
48 To calculate the average: Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)
49 Composition of the nucleus Atomic MassesAtomic mass is the average of all the naturally occurring isotopes of that element.IsotopeSymbolComposition of the nucleus% in natureCarbon-1212C6 protons6 neutrons98.89%Carbon-1313C7 neutrons1.11%Carbon-1414C8 neutrons<0.01%Carbon =
50 Law of Multiple Proportions If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H2O and H2O2.Law of Constant ProportionsEvery pure substance always contains the same elements combined in the same proportions by weight
51 Law of Multiple Proportions If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. (not decimals) For example, H2O and H2O2.Law of Constant ProportionsEvery pure substance always contains the same elements combined in the same proportions by weight
53 The Periodic Table: A Preview A “periodic table” is an arrangement of elements in which the elements are separated into groups based on a set of repeating propertiesThe periodic table allows you to easily compare the properties of one element to another
54 The Periodic Table: A Preview Each horizontal row (there are 7 of them) is called a periodEach vertical column is called a group, or familyElements in a group have similar chemical and physical propertiesIdentified with a number and either an “A” or “B”More presented in Chapter 6