Chapter 1

Chapter 2Part A

Atomic Theory of Matter 2.1Atomos = indivisible or uncuttableDemocritus (4th to 5th C. Greece)

Idea disappeared until 17th C. Europe

Daltons Atomic Theory 2.1

3The total mass of materials present after a chemical reaction is the same as the total mass present before that reaction.=Law of Conservation of Mass

4In a given compound, the relative numbers and kinds of atoms are constant.=Law of Constant Composition

All lead Dalton to conclude:Law of Multiple Proportions 2.1If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers

Early History of Subatomic Particles 2.2Particles which compose atoms

no direct evidence for existence of atoms and certainly not their composition until until 18th to 19th centuries

Brief History of Subatomic Particles 2.2

Mid to late 1800s: Thompson: cathode ray tube: high voltage in a vacuum tube caused particles in tube to fluoresce

Experiments showed that rays were deflected by electric and magnetic fields

Brief History of Subatomic Particles 2.2Must be charge = discovery of electron (Thompson)Also able to calculate 1.76*108 C/g = charge/mass of e-

Early 1900s: Robert Millikan determined individual charge and mass of e-1.602*10-19 C9.10*10-28 g (2000 times smaller than mass of H)

Radioactivity 2.2Late 1800s: Becquerel discovered that U compounds (oxides and others) spontaneously emit high energy radiationCuries studied to isolate radioactive componentsNobel Prize in 1903 jointly with Becquerel

Marie Curie: second Nobel Prize in 1911 for her discovery of Po and Ra

Radioactivity (contd.) 2.2Later: Rutherford differentiated 3 different types of radiation: rays are unaffected, rays are bent by an electrical field(+ plate attracts raysopposites attract)

Similar to X rays: no particles nor chargeNuclear Model of Atoms 2.2Thompson2: since e- are small part of atomic mass must be small part of its sizeNuclear model of atom via scattering experiment (+ of nucleus repels + of particles)

Finally 2.2By 1930s determined nucleus contained: protons+ and neutronsElectrons - circulated outside

Discovery of Atomic Structure 2.2

Si atoms, post-1965Modern View of Atomic Structure 2.3Only 3 particles which affect chemical behaviorCharge of electron = charge of proton and we typically report as -/+ 1 Charge of neutron = 0Why then does atom have no net electrical charge?Atomic Structure 2.3

Outer sphere electrons Attracted to nuclear protons;Strength of these forces can Explain elemental differencesMajor role in chemical reactions Atomic Mass Unit 2.3Unit of mass for atomic particles since1 amu = 1.66054*10-24 g

*Most of atomic mass in nucleus*Atomic Diameter 2.3Atom:1-5 1 = 1*10-5 mNucleus:DENSE:1013 1014 g/cm10-4 = 0.0001

nucleusH atomAtomic Number1, Mass Number2, Isotopes3 2.31--Elements are differentiated by number of protons (+) in their atoms = number of electrons (-) same for all atoms of one element2--Elements also differentiated by number of neutrons () and protons (+) 3--Atoms with same atomic number but different mass number (different number of neutrons)

Atomic Mass 2.419th Century:Dalton suggested 1H as first relative atomic masslater improved this to state relative atomic mass in terms of 1H = 1/16 O (since O in many known compounds)Because of debates and uncertainties, in 1961:Definition of amu:Mass 12C = 12 amu Therefore, by this standard, mass 1H = 1.0078 amu 16O= 15.9949 amu1 amu = 1.66054*10-24 g1 g = 6.02214*1023 amu

Atomic Weight 2.4Several isotopes for most elementsAverage atomic mass = atomic weight= (atomic mass of isotope) * (isotope abundance)(for all known isotopes of THAT element)

Periodic Table 2.5Developed 1869 significant chemical tool to this day 2014Periodic patterns when arranged by atomic number

Soft, reactive metalsnon-reactive gases123non-reactivecoinage metalsGroup Names 2.5

More About Periodic Table 2.5Metals: lustrous, high conductivity, solids at 25 C

Metalloids: intermediate propertiesNon-metals: differ from metals in many physical propertiesS,L or G at 25 C

Group Problem 1 Selenium is sold as a dietary supplement. It is widely advertised to protect women from breast cancer. Write the nuclear symbol for naturally occuring selenium. It has 34+ and 46 .Group Problem 2U 235 is the common isotope for uranium used in nuclear power plants. In the atoms:How many + and where are they?How many and where are they?How many and where are they?Group Problem 3From sample exercise 2.4Three natural isotopes of Si are: 28Si (92.23%), atomic mass 27.97693 amu; 29Si (4.68%), atomic mass 28.97649 amu; 30Si (3.09%), atomic mass 29.97377 amu.Calculate the atomic weight of Si: